Our greenhouse full of seed flats and sunshine in March. Spring transplants offer a great way to get ahead of weed growth. Photo Twin Oaks Community
In February the days got visibly longer and our spring planting dates got closer. I wrote about monitoring the weather forecasts to seize the best opportunities to prepare the soil where you plan early crops, as soon as it is dry enough. Timely soil prep and timely planting avoids losing ground to weeds. Flaming, transplanting and relay planting can all help make best use of opportunities.
In JanuaryI wrote about planning and preparing for weeds. I wrote about mowing; sowing oats where you have no cover crop in place and you don’t need to plant crops for 6-8 weeks; the stale seedbed technique; tarping; flaming; steaming; and using time to repair, maintain and sharpen tools you’ll be relying on all season. In December I included some info on Crop Rotations to reduce weed problems.
Now March is here and the cool weather weeds will use every opportunity they get to cover bare soil. We will need to out-fox them! That is, we need to be smart.
For our silty clay loam to be tillable with our BCS, the soil needs to be dry enough that a handful of soil formed into a ball will break when dropped on the ground from waist height.
Iowa State University Integrated Crop Managementsays : When soil is dry enough to be tilled, a ribbon of soil pushed out between the thumb and index finger will break before it reaches 5 inches in length. Likewise, soil made into a ball will break apart when thrown into the air. If the soil is too wet, it is more “plastic” and fails these tests.”
Tempting as it may be to till wet soil, you are creating problems for your future. Soils worked wet will compact and not drain well. They will crust and crack, and once dry, not absorb water easily. Roots won’t be able to grow well through that soil, and so plants won’t be able to absorb nutrients easily. If the soil is only just dry enough to till, you may be able to “open it up” by doing a once-over rough tilling, then going away to wait for the situation to improve. This may only take a day or two. It’s much wiser than determinedly beating the soil with multiple passes.
If your tiller tines are picking up a lot of soil, this is a sure sign of tilling too soon. If the soil on your tines is forming little balls or pellets of soil, this is another sign. Discretion is the better part of valor! Stop. Do something other than tilling!
If you use two boards to stand on in turn, you may be able to roughly broadfork the area. Stand on one board, and when you need to move that board, position the second one, step on it, work and repeat. This two-board trick is useful on paths in raised bed areas when the soil is wet. The boards spread your weight, reducing compaction. Be standing on one board or the other. Don’t try to fudge things with only one board.
Don’t work in mud, or let your cows walk through when the garden is muddy! Photo Wren Vile
An earlier start is possible (and wise) in raised beds
In our raised bed area we use a walk-behind BCS rototiller, which can (if we have to) work in slightly wetter soil than a ride-on tractor. We still do the ball-of-soil test. One advantage of raised beds is that the soil dries out quicker, so we can work in the raised beds sooner after rain than we can in the row crop areas.
In early spring, don’t wait until just before you want to plant to prepare the soil! This is one time when maximizing the lifespan of the cover crops might not be the smartest thing. In cooler weather, soils stay wetter longer after rain. Be ready for the possibility that it will rain more than you’d like between now and planting day! Start 2-3 weeks ahead, spreading compost on the early beds. You can use the two-board trick in the paths between the beds. You can fill the barrows only half-way, to reduce the compaction and the chance of tipping over. Shovel compost out onto the beds as you go. This works better than dumping out the barrow and spreading from the heap, if the soil is wet.
Potatoes, weeds and standing water. Until the soil drains, the potatoes cannot be hilled, and the weeds here are already large. We could flame the weeds if access becomes possible, and the potatoes are less than 8″ tall. Photo Bridget Aleshire
Flaming for weed control in wet springs
As well as pre-emergence flaming to kill weeds in beds of slow crops like carrots, flaming can be used to kill larger weeds in areas where you can’t yet work the soil. Between raised beds, this is another use of the two-board strategy, either for the operator of a hand-held wand or to walk while Carrying the propane cylinder and pushing a rolling flamer on the bed top. One year we even flamed our whole potato patch because it was too wet to hill and weeds were growing fast and flowering. This can work if the potato plants are 8″ tall or less. This photo shows vines a bit too big for that trick.
Transplanting helps us deal with weeds
We transplant many spring crops because we can get earlier (therefore longer) harvests that way. The seedlings grow faster in our greenhouse or hoophouse than they would if direct seeded. Our springs heat up fast, and we will get more to eat before cool weather crops become a lost cause. This is particularly important for spinach and Asian greens which bolt quickly in our climate. Even broccoli benefits from a transplanted start, giving more growing time before hot weather. Once the weather heats up, broccoli becomes bitter.
Organic Weed Management Topics from eOrganic
eOrganic has a treasure trove of info on weed management. Each of these topic nodes leads to a further 8-20 publications.
If you can replan your crops, you could use black plastic tarps for 3 weeks in spring and prevent new weed growth for that time. Whatever crop remains or cover crops you had will not have disappeared, but at least you have prevented more weeds from growing, and more rain from sinking into the soil.
We transplant all our spring spinach, to maximize the length of the harvest period Photo Denny Ray McElyea
In December I wrote about noxious weeds and included some info on Crop Rotations to reduce weed problems. In JanuaryI wrote about planning and preparing for weeds. I wrote about mowing; sowing oats where have no cover crop in place and you don’t need to plant crops for 6-8 weeks; the stale seedbed technique; tarping; flaming; steaming; having a full year of cover crops, mowed regularly; and using time now to repair, maintain and sharpen tools you’ll be relying on all season.
February is much like January here, except that the days are getting visibly longer and our spring planting dates are getting closer.
Monitor the weather forecast, be ready to act
We want to plant early crops in March, so we are looking out for opportunities to prepare the soil when it is not too wet. In our row crops area, we will plant potatoes in mid-March. That’s a large area, needing tractor work to turn under the cover crops, then again to add some compost and make the soil friable enough to make furrows. The soil will need to be dry enough that a handful of soil formed into a ball will break when dropped on the ground. Because spring weather is so variable here, and the cover crops will break down slowly in the cold soil, we try to start as soon in February as weather permits. The gap between the first round of disking and the second might germinate some weeds, which can get killed by the second round. The later hilling of the potatoes (twice) will remove more weeds.
Frosted potato plants May 10., after two nights at 30F and 29F. If you know a frost is coming, try to get the potatoes hilled, which protects more of the stem and leaves under the soil. This increases the likelihood they’ll be able to grow back. Photo Pam Dawling
An earlier start is possible in raised beds
In our raised bed area we use a walk-behind BCS rototiller, which can (if we have to) work in slightly wetter soil. We still do the ball-of-soil test. One advantage of raised beds is that the soil dries out quicker, so we can work in the raised beds sooner after rain than we can in the row crop areas. We can start well ahead of the planting dates, spreading compost on the early beds. In February (assuming we can get the beds ready in time) we will be sowing our first bed of carrots and transplanting spinach.
A young carrot bed in April, ready to hoe and thin. Photo Pam Dawling
Flame-weeding the carrot beds
Carrots are slow-growing and it pays to choose a bed we know is fairly clean of weed seed, so we don’t lose our carrots. This is where flame-weeding really helps. We spread compost, till the bed, sow the carrot seed and a few beet seeds at the end near the path, and flame the bed as soon as we see the easily-recognized beet seedlings. As beets take one day less than carrots to germinate at almost any temperature, as long as we don’t see carrot seedlings that day, success in killing the weed seedlings (including the invisible ones just below the surface) is ensured. The first time I flamed a carrot bed and saw the results, I announced to the world at large “This feels like cheating!”)
Small spinach seedlings for bare root transplants. Photo Pam Dawling
How transplanting helps us deal with weeds
We transplant our spinach because we can get faster growth that way. The seedlings are in the ground in our hoophouse, and grow faster there than they would outside, making some growth whenever the air temperature is above 40F (5C). Our springs heat up fast, and spinach will bolt when that happens. By starting earlier than we could outdoors, we will get more to eat before spinach becomes a lost cause. Secondly, there is the advantage over the weeds. We can prepare the soil, turning under the weeds. Our last worthwhile date for transplanting spinach is April 8, although we do hope to be done weeks before that. The relatively large transplants have a head start over any newly emerging weed seedlings. In sunny dry and breezy weather, we will hoe around the spinach plants.
Clumps of scallion transplants in a plug flat, ready to transplant. Photo Pam Dawling
Other early March transplants include scallions, the first lettuces and early cabbages. Cabbages and lettuces are big enough to tolerate some weeds seed jumping into action, as long as we are ready to hoe when we can. Using some kind of measuring device, and planting at regular spacing in straight lines makes hoeing faster and more effective, with fewer accidents (“Eat your mistakes!”). We sometimes mulch the cabbages, accepting that this will keep the soil cooler and perhaps slow down the early growth. For earlier cabbages, it is better not to mulch. Choose fast-maturing varieties and treat them well. We like Farao and Golden Acre. We are trying again to get an early red cabbage. Red Acre is this year’s candidate.
Relay-planting reduces weeds, as well as soil inversions
Spinach and peas in a relay planting scheme. Photo Twin Oaks Community
Also in early March we will be sowing Sugar Ann snap peas. Our best weed management strategy for those is to sow them down the center of a bed of overwintered spinach. The spinach bed (direct-sown in September) will have been hoed in the fall and early winter, so fewer winter annual weeds will germinate in spring. The rowcover on the spinach all winter will have warmed the soil and will protect the germinating peas. We remove the rowcover when spring warms (we don’t want to overheat the spinach!) and we stake the peas. This relay-planting leads to a bed of peas once the bolting spinach has been hoed off.
As you see, weed management can be achieved in various ways, and choosing the best method to fit each crop and its management is part science, part art.
Oh dear! Lettuce with weeds, easily hoed, but better avoided.. Photo Bridget Aleshire
In December I wrote about noxious weeds and included some info on Crop Rotations to reduce weed problems. In January weeds are not growing fast. We can use the time to plan and prepare.Planning to reduce weed problems
This is a good time to walk your gardens or fields, take notes of potential early weed sites and make a plan. Seedlings of thosewinter annual weedsmay already be present. Also review your crop records and list weed problems that came up last year and where they were worst. Study your crop rotation plan and decide if any of the weed problems are serious enough to justify setting aside your plan and foregoing the crops you were going to grow there, in favor of dealing with the weeds in that area. Perhaps you can juggle crops around, so you can keep your more important crops and skip the arugula this spring.
Strategies to reduce weed problems
A honeybee on deadnettle weeds. Notice the chickweed buds too. Credit Kathryn Simmons
If you see or expect winter annual weeds you can switch plans to plant a fast-growing spring crop there, one that will smother new emerging weeds. Or plan a later food crop and get rid of the early weeds first.
Anytime you see weeds flowering, try to mow or weed whip to prevent seeds forming. I remember being new here, and gazing in horror at many raised beds without cover crops or food crops, but covered in purple flowers of dead nettle and hen bit (and a little ground ivy). It had not occurred to me to mow.
Another option (if the soil is not too wet or frozen) is to till the weeds under and sow oats cover crop and let them grow for 8 weeks before turning them under in time to plant your food crop. If it’s too wet to till, consider flaming.
If you don’t have 8 weeks, you can use the Stale Seedbed Technique: till the bed, water if nature doesn’t; repeat in a couple of weeks. This is not great for the soil and its resident micro-organisms, so be mindful of why you are doing it, and use it as a short-term strategy.
Or you can tarp the area. Tarping (or solarizing in hot weather) can be effective ways to deal with weeds. See my 2021 post Dealing with Weeds.
Dandelions are a perennial weed with seeds that blow and spread easily. Wish we’d mowed these last year! Photo Wren Vile
In our hoophouse we have a mantra “Let no weed flower” and we try to pull weeds as we harvest. The hoophouse doesn’t have many weeds, but that’s because we are more diligent in there than outdoors, and pulling weeds as we go does not slow us down much. Plus, we can lay the weeds on the soil in there and they will cook. Not always true outdoors!
Our year-round clover patch really helps us. The annual weeds get mowed while the clover regrows. Regular mowing (once a month March-October in our climate) will dispatch annuals and new biennials. If you can fit a full-year of cover crops somewhere in your rotation, this can help reduce weeds long term.
January is a good time of year to round up your tools and get them in tip top working order.
Sand and oil wood handles with linseed oil. Remember linseed oily rags can self-ignite, so burn them safely or possibly bury them, if the rag is bio-degradable. If you use linseed oil often, you can submerge your rag in the oil and put a lid on the container.
Sharpen blades with a file or a sharpening stone or a grinder wheel if you really need to. This is a fast way to wear down your tools, so to maximize tool life, use the method that removes the least metal necessary to get the result you need.
Using the Berta rotary plow to make paths between our raised beds. Having reliable machinery involves care and maintenance. Photo Pam Dawling
Do a thorough maintenance of all power equipment, so the tools are ready to use when the time comes. This will avoid any temptation to “Just see if it starts right up” and use it without good treatment.
Inventory your supplies of parts and materials such as nylon line for the string trimmer, and buy what you need.
Eat the weeds!
Yes, some weeds are edible, and harvesting them will prevent them taking over, if you eat enough. Personally, I think this strategy is over-rated, as weeds like chickweed, although fun and nutritious, quickly get stringy and old. By that point they have shed many seeds. So, if you have weeds you like to eat, cut them down young and set a bowlful aside to eat, but be sure you have cut them all down. Or maybe you can throw the whole bucketload over the fence to the chickens and they will eat them all.
Chickweed flowers. http://ipm.ucanr.edu/PMG/S/W-CP-SMED-FL.006.html Photo by Jack Kelly Clark.
December is a good opportunity for tackling invasive noxious weeds. Go beyond your gardens, walk over your land and, while leaves still remain, monitor for noxious weeds, especially designated Federal Noxious Weeds. Search online for noxious weeds/state name or go into your Extension Service office while in town.
In Virginia we have a good publication Identification of Virginia’s Noxious Weeds. Looking through that document, I am selecting weeds I know we have trouble with in Louisa County: Japanese Stiltgrass, Mile-A-Minute Vine, Oriental Bittersweet and Tree of Heaven. One not included in that document is Trumpet Vine, aka trumpet Creeper, one I have seen pop up in garden plots.
After descriptions of these weeds, I’ll cover some seasonal weed management topics: crop rotations, and soil steaming
In colder areas, Japanese Stiltgrass dies in the winter. Experiments show that using dry ice in late August in New York State, kills Japanese stiltgrass and may prevent reinvasion for a few years. Not so, where I am!
It grows on the edges of damp woodlands, stream banks, ditches, fields starting to return to woodland, powerline corridors, and, yes, gardens. It is a grass with short lance-shaped leaves arranged alternately on a branched stem heading in a thin spike of flowers or seeds in season. It looks quite delicate and attractive, but each plant can produce 100-1000 seeds, which can persist in the soil for 3-6 years. It can take over! Areas that get infested with Japanese Stiltgrass have decreasing biodiversity, except for other invasive plants and invasive animals. Native wildlife does not choose to graze on this weed.
If you have the beginnings of an invasion, act this year. Mowing to prevent seeding can buy time where the plant is fairly newly established. Roots are shallow, but avoid incorporating seeds by tilling. Action is best taken before seed set, otherwise the plants will need to be hand-pulled and removed.
Covering stiltgrass with 4”-6” of mulch (chips, leaf litter) will prevent stiltgrass from emerging. As the mulch starts to decompose, broadcast seed of a native grass or other suitable plant, into the mulch. Tarping may work, as roots are shallow.
Persicaria perfoliata (L.) H. Gross (formerly known as Polygonum perfoliatum L.) aka Asiatic Tearthumb. This fast-growingvining weed grows dense mats that smother native species. Here’s a video from the USDA National Invasive Species Information Center.
is a climbing woody vine with attractive red berries in orange coats. It can suffocate trees. It spreads by seeds and by roots. Leaves of Oriental Bittersweet are often smaller than native bittersweet. The berries of oriental bittersweet grow up and down the stem with the leaves. See the photo. American bittersweet often has larger, elliptical leaves and the fruit develops at the end of the stem.
Tree of Heaven. Photo: Nature Conservancy
Tree of Heaven, Ailanthus altissima, aka stinking sumac, is devilishly invasive, and is harboring the Spotted Lantern Fly. The ailanthus produces copious quantities of seeds, and inhibits and crowds out native plants nearby. Its roots exude a chemical that is toxic to other plants.
Spotted lantern Fly lifecycle stages. Photo Virginia Tech Extension
The invasive Spotted Lantern FlyLycorma delicatula,,seeks out the tree of heaven as a place to lay eggs. This insect feeds on and damages many species of native and fruit-bearing trees, especially those with sweet sap, such as grapes and maples. Click the link for lots more resources about the Spotted Lantern Fly, including a map of Virginia showing which areas have infestations. Your own state Extension Service, or Fish and Wildlife Service will provide similar info. Note that quarantined areas have restrictions on the movement of plants, wood chips, firewood, outdoor furniture and much else.
The tree of heaven springs up quickly after disturbances (such as extreme weather or infestations of spongy moths). The climate catastrophe is leading to more extreme weather like stronger storms and longer droughts, which allow the spongy moth to thrive.
There are multiple ways to control the tree of heaven. The most effective way is to pull up or dig seedlings before the taproot develops. If the plant has matured, cutting it down will help temporarily by reducing its ability to spread by seeding. The roots must be removed to stop the tree regrowing.
Be sure to correctly identify the tree of heaven, as it looks similar to some native species such as sumac, ash and black walnut, which also have pinnately compound leaves arranged in pairs across the stem. Ailanthus can be distinguished from these native species by its fuzzy, reddish-brown twigs and clusters of light green seed pods.
is an aggressive woody vine that climbs or sprawls, depending on the vegetation available. It can climb high in trees using aerial rootlets,and also infest pastures. The flowers are attractive to people and to hummingbirds! Its rapid colonization by suckers and layering makes it useful for erosion control, but its problems may be worse than its good features. Although deliberately cultivated in some colder areas, in the Southeast its aggressive habit has earned it the names of Hellvine and Devil’s Shoestring.
Crop Rotations to reduce weed problems
By planning a crop rotation that mixes up the seasons of crop growth each year, you can reduce the chances of weed seeds germinating. Try to have early season food crops one year followed by late season food crops the next year. With cover crops in between. This is known as “phenologically diverse crop rotations.”
Crop Rotation Pinwheel for Twin Oaks garden
Our own crop rotations, planned to maximise opportunities for cover crops, especially legumes, tend to have several years of early spring food crops (cabbage, broccoli, spinach, kale, March-planted potatoes) which finish by July, allowing us to plant cover crops mixes based on oats in August, which may winter-kill and allow more early food crops the next year. Likewise the food crops planted in warm weather yield until frosts, by which time it is too late to sow oats, and we go with winter wheat and crimson clover or Austrian winter peas, which we turn under in late April. This sequence naturally works easiest when more late-planted food crops follow. If you have a bad weed problem, you might decide to forego best cover crops for a few years. Our year-round clover mix really helps us. The annual weeds get mowed while the clover grows.
Tarping or solarizing can be effective ways to deal with weeds. See my 2021 post Dealing with Weeds.
Soil steaming is a relatively new practice, and the equipment is expensive. The ATTRA publication discusses trying this in high tunnels (hoophouses) where the space is of higher value than outdoors, and grants were available.
The goal is to pasteurize the soil, not kill everything. Holding the temperature at a minimum of 140°F for 30 minutes provides fungal and bacterial pathogen control. Chickweed and soilborne pythium (damping off) control also occurred at 140°F. If the temperature gets too hot, the steam can kill beneficial nitrifying bacteria.
This is an emerging technology I mention for the pioneers reading this and for the rest of us to keep an ear open for developments. Perhaps this kind of equipment could be shared by several farms, or rented out.
Excerpt from Manage Weeds on Your Farm:
“Like flame weeders, steam and hot water weeders kill by disrupting plant surfaces, leading to subsequent desiccation. Their advantage over flame weeders is that the flame is enclosed in a boiler, which minimizes risk of starting a fire. Their energy use, however, is several fold higher per acre than typical flame weeders. Hot water weeders are more energy efficient than steam weeders because they do not bring water to a boil, but steam weeders require a smaller volume of water. Although hot water and steam weeders are finding some acceptance for urban weed management, adoption rates in agriculture have been low due to their high fuel usage and the potential soil compaction from hauling large volumes of water over tilled fields.”
Mugwort and Bermuda grass (wiregrass) Photo Pam Dawling
This month I am going to write about tackling some summer perennials, especially quackgrass (couchgrass), wiregrass (Bermuda grass) and mugwort. November is a good opportunity for digging our invasive wandering perennials.
In October I wrote about winter annual weeds, mostly Henbit, Ground Ivy, Purple Dead Nettle and Chickweed. In September I wrote about late summer weeds, chiefly purslane, velvetleaf, flower of an hour, horsenettle, fall panicum and johnsongrass. In August, I wrote about nutsedges and mugwort; in July, pigweeds (amaranths), warm weather annuals that put out seeds in a “Big Bang” as Chuck Mohler describes in Manage Weeds on Your Farm. In June, I wrote about docks; in May, galinsoga.
Reducing the strength of perennial weed roots and rhizomes
Perennial weeds can often regrow from pieces of roots or rhizomes left in the soil after tillage or digging. Rhizomes look like roots, but they are different. Rhizomes are modified stems, usually growing underground, with roots from each node and buds that can develop into new shoots. Disturbances such as digging and tilling break the dormancy of those buds. In creeping perennials, the roots or rhizomes store carbohydrates that sustain the underground system over the winter and provide fuel for a rapid start up next spring.
When a rhizome grows a shoot, plant hormones from that shoot prevent other nearby nodes or buds from sending up shoots. This is called apical dominance (the node at the apex dominates the other nodes into not sprouting). These chemical messages get weaker over distance, so that, on long rhizomes, after a certain length, the dominance effect is too weak and another node can produce a shoot. That shoot, in turn, also produced hormones preventing nearby buds sprouting. The result is that long rhizomes have a fairly regular distance between shoots.
When rhizomes are cut into little pieces during tillage, the apical dominance applies to each piece, and it can grow one terminal shoot. This is not necessarily as disastrous as it sounds because these are small, weak plants with only a small source of nutrients. They won’t all make it to the soil surface and grow. The danger is in walking away at this point and leaving them to grow.
If we cultivate again before the new shoots have grown enough to send energy back to the roots, or manually pull out the pieces to dry out on the surface, the depleted pieces of root or rhizome may die. Repeated cultivation can chop the rhizomes into small pieces and bury them deeper in the oil. This makes it less likely that the pieces will have the reserves to grow to the surface and thrive.
The strategy is to weaken the root pieces until they give up. Repeated cultivation and drying on the surface can both achieve this goal. This strategy doesn’t work for stationary perennials such as docks and dandelions, which have relatively thick roots, with bigger food stores. Deep burial of taprooted perennials is often an effective first step despite their large food reserves. The storage roots and rhizomes of wandering perennials are not much affected by a change in orientation, but taproots grow vertically in the soil, and if inverted or laid on its side sideways deep in the soil, it first uses energy to develop a new vertical axis. Most tap-rooted perennial weeds grow a rosette of leaves at ground level before growing a flower stalk. Disturbed taproots need substantial food reserves to manage this recovery. See Weeds for June for more about docks.
Bermuda grass has long roots, which can be gathered with some kind of rake or tined cultivator. It is a warm weather grass, and exposure to cold temperatures will at least set it back.
Mugwort has fat, very brittle roots which snap easily. These need to be eased out of the soil and taken away. They don’t dry out easily. We lay ours out on the driveway to dry and get run over by vehicles.
Even simply removing top growth whenever the weeds reach the 3- or 4-leaf stage can be quite effective in further weakening invasive perennial weeds. This may need to be done several times at 3- or 4-week intervals to knock out a bad infestation. For quackgrass, the 3-leaf stage is the time to act. It’s more effective to wait each time until the new top growth has drawn down the plant’s reserves (in the roots) before hoeing or pulling, than to go almost daily after every sprig. Thickly planting buckwheat or other smothering cover crops immediately after tilling helps put extra pressure on the weed, and can reduce tilling passes.
Here is a drawing from Manage Weeds on Your Farm: A Guide to Ecological Strategies, published by SARE
Climate change and C3 and C4 plants
Most plant species (85%) use C3 photosynthesis, meaning the molecules of the first carbon compound produced during photosynthesis have three carbon atoms. During photosynthesis, these plants release water vapor through the stomata, in a process called photorespiration, leaving C3 plants at a disadvantage in high temperature conditions. C3 plants are adapted to cool seasons in either wet or dry environments, not needing full daylight to maximize their photosynthesis. About 25% of the carbon that is fixed by C3 plants may be lost as CO2 in photorespiration. Nearly all trees are C3 plants. C3 grasses have greater frost tolerance than C4 grasses. C3 food crops include spinach, peanuts, southern peas, soybeans, wheat, rice, barley, and cassava.
Common Purslane, a C4 weed. Photo Virginia Tech Weed ID
C4 plants, which produce molecules of a four-carbon compound, are more adapted to warm or hot weather, moist or dry. They are able to avoid photorespiration, conserving more water. Although many weeds are C3, some of the most competitive ones use C4 photosynthesis. Purple and yellow nutsedge, crabgrass, Bermuda grass, foxtails, pigweeds, and common purslane are C4 plants. C4 food crops include cabbage, corn (maize), millet, sugarcane and sorghum. Weed Science has a 1983 article “Composite List of C4 Weeds” by C. D. Elmore and R. N. Paul. Cornell also has Weeds and Climate Change in their Weed Science department.
The RIPE project is working to improve photosynthesis in C3 crops, for greater food security under climate chaos. Because the growth of C3 plants is limited by available carbon dioxide, they may benefit when levels of carbon dioxide in the atmosphere are higher due to the climate disaster. This benefit may be outweighed by drought stress caused by the increase in temperature. During drought stress, plants close their stomata to conserve water and keep themselves alive, necessitating sacrificing any carbon dioxide intake during that time (meaning photosynthesis shuts down and the plant stops growing).
There is a third photosynthetic pathway, called the Crassulacean acid metabolism (CAM) pathway. CAM plants are succulents, suited to dry, arid conditions..
In September I wrote about Late Summer Weeds, chiefly purslane, velvetleaf, flower of an hour, horsenettle, fall panicum and johnsongrass. In August, I wrote about nutsedges; in July, pigweeds (amaranths), warm weather annuals that put out seeds in a “Big Bang” as Chuck Mohler describes in Manage Weeds on Your Farm. In June, I wrote about docks; in May, galinsoga.
Types of weeds: six ways to categorize them
Annuals and perennials: we have looked at some annuals: galinsoga, pigweed, purslane, flower of an hour, and fall panicum, and some perennials: horsenettle, johnsongrass, nutsedge and docks. The tap-rooted perennials, such as docks, grow a vegetative plant the first year, then flower and seed and grow bigger every year after that.
Stationary perennials (docks) and invasive perennials: (we have looked at johnsongrass, nutsedge, and horsenettle);
Cool-weather and warm-weather types. We’ve mostly looked at warm weather types since this blog series started in May: pigweeds, purslane, velvetleaf, flower of an hour, horsenettle, fall panicum and johnsongrass and also galinsoga. Docks grow year-round, persisting as a rosette of leaves over the winter after flowering and seeding.
Quick-maturing and slow-maturing types: galinsoga is notoriously fast, but is very sensitive to frost; biennials like docks and dandelions do not produce seeds the first year.
“Big Bang” types (pigweed) that spend time growing large before making and dispersing thousands of seeds, versus “Dribblers” (galinsoga) that start putting gout seeds at a young age and keep going until stopped.
This month I am going to write about winter annual weeds such as Henbit, Ground Ivy, Purple Dead Nettle and Chickweed. I wrote about three of these weeds in late August 2016, when I was awaiting their germination as a sign that the soil was cooling down enough to sow spinach. The maximum germination temperature of these weeds is the same as that for spinach. No point in sowing spinach sooner.
Sometimes people confuse henbit, ground ivy and dead nettle, as they are a similar shape and size; all have purple flowers and all can grow together in similar conditions. Here’s a really useful blogpost from Identify that Plant on distinguishing these three easily mixed-up early spring plants. This site has really helpful photos, and videos.
Here are photos of chickweed, henbit and dead nettle seedlings. These are the three I look for when deciding if the conditions have become suitable for sowing spinach.
Purple Dead Nettle seedling. Photo by Plantevaern Online
See how closely the dead nettle seedling resembles the henbit? And see the differences, the way the seed leaves come off the petioles, and the overall shape of the true leaves?
Henbit (Lamium amplexicaule)
Henbit is a spring and winter annual weed here.
Henbit flowers grow from the leaf axils in a pair, foursome or a whorl around the stem. This is easiest to see when the flowers are still buds. Buds are redder than dead nettle or ground ivy buds. The whorls overlap closely at the top of the plant, and are more spaced lower on the plant, giving a good view of the square stem. Henbit has a distinctive deep red stem color.
Henbit flowers, Lamium amplexicaule. http://ipm.ucanr.edu/PMG/L/W-LB-LAMP-FL.004.html Photo by Jack Kelly Clark.
Henbit and purple dead nettle have very similar flower shapes. They are both in the mint genus (Lamium), as is ground ivy. The biggest difference between the two flowers is that henbit flowers have a long tube section. This is easiest to see when the flowers are fully open.
Henbit leaves grow in pairs opposite each other on a square (mint) stem. They also are sessile (growing directly from the stem without any petioles). The leaves form “galleries” around the stem. The leaf margins are deeply scalloped — far more than ground ivy’s leaf margins. Henbit leaves are smooth and look more glossy than dead nettle and ground ivy. Some lower leaves do grow singly with a petiole (leaf stem), as in the seedling, above.
This plant’s growth habit is low and sprawling like ivy. This one is a perennial, less common in our vegetable garden and more common in untilled areas such as sparse lawns. It needs to be physically removed, either piece-by-piece, or in mats on a spade or sod-lifter.
The ground ivy flower is bilateral (like a tiny tubular pansy) in shape, with lower and upper petal lips. It is more of a blue color compared to henbit and purple dead nettle flowers.
Some plants have two flowers at each pair of leaves while others have a whorl 3-6 flowers. The flowers in a whorl do not all bloom at once.
Ground ivy leaves are rounder than dead nettle and henbit leaves, and they are hairy. The stalked leaves grow opposite each other in pairs off the stem. If bruised, the stem and leaves have a strong smell.
Purple dead nettle (Lamium purpureum)
Flowering Purple (or Red) Dead Nettle, with honeybee, and seedling chickweed. Credit Kathryn Simmons
This plant is easily mistaken for henbit or ground ivy. The hairy leaves are arranged oppositely along the stem. The leaves at the top of a plant are often lavender, red or purple rather than green. The younger leaves crowd each other, overlapping at the top of the plant.
Although the leaf veining looks very similar to ground ivy, the dead nettle leaf shape is more like a heart — less rounded and more pointed. The leaf margins of purple dead nettle are not as deeply scalloped as ground ivy’s.
Dead nettle flowers are similar to the ground ivy flowers, in being bilateral with lips. However, the lip structure is different.
Common chickweed (Stellaria media)
Chickweed flowers. http://ipm.ucanr.edu/PMG/S/W-CP-SMED-FL.006.html Photo by Jack Kelly Clark.
Chickweedis not in the mint family. It looks quite different, has small star-shaped white flowers, but grows in similar conditions to the purple-flowered weeds. It sets seed very rapidly. An important identifier for Common chickweed is the single row of hairs along its stem. There are other chickweeds, such as mouse-ear chickweed and star chickweed. Yes, I know it’s edible, so go right ahead. You’ll find that while it is pleasant when young, it soon becomes stringy and less succulent. The string runs inside the stem, and is an indicator of true chickweed. In Australia there is a poisonous look-alike, radium weed, Euphorbia peplus
Chickweed has thin round stems, smooth oval leaves (unless mouse-ear) attached in opposite pairs to the stem.
Chickweed sprawls over the soil, making it hard to kill by mowing.
Managing winter annual weeds
The goal here is not to let these weeds seed, or you will have problems for years to come.
In the fall, you can hoe these weeds while small, if you have very dry weather. They easily re-root in damp weather, so if in doubt, pull them out by the roots, shake the soil off well, and either take them to your compost pile, or lay them out on an area that has thick organic mulch. Get a winter cover crop established as soon as possible, to out-compete the weeds. With some crops you may be able to undersow the cover crop before the food crop is finished. This can work for tallish crops, where the sunlight reaches the soil. It does not work for vining crops that cover the ground. For small crop plants in rows, you may be able to undersow a cover crop in rows that run in between your food crop rows. Experiment and keep records. You will need a robust fairly fast growing food crop, and a cover crop that is not too robust. And of course, you will need a cover crop that is suited to your sowing date.
Weeding rowcovered spinach in winter. Photo Wren Vile
In the winter, you can handpull weeds as in the fall. If you have a spell of sunny breezy weather, you could try “shingling” the weeds on the bed. Start by laying the roots of the first weed you pull on an impervious surface such as a rock, or a piece of wood. Lay the roots of your second weed (after shaking off the soil) on the top (leaves) of the first weed, so that the final effect will be of lines of roots exposed to sun and wind, unable to touch the soil. If the weather changes for the calmer, cooler, damper, you’d be wise to go and gather up all the weeds in a barrow and take them to the compost pile. If left, the seeds will continue to mature and the roots will try to grow back into the ground.
In the early spring you can use a mower, scythe or weed whacker to stop the weeds seeding. If you have 6-8 weeks before that bed will be used, you can till and sow oats. If you have only 2-3 weeks until crop planting time, you can till, wait until just before planting, and till again.
Baker, B. and C. Mohler. 2015. Weeds Your Way: How Upstate New York Organic Farmers Manage Weeds
Birthisel, S.K., E.R. Gallandt, A. E. Souza Cunha. 2018. Solarization and Tarping for Weed Management on Organic Vegetable Farms in the Northeast USA.
Colley, M. A. Stone, and L. Brewer. 2009.Weed Management in Organic Seed Production.
Leslie, A. G. Chen, C. Hooks. 2016. Organic Integrated Weed Management in Vegetables.
Puka-Beals, J., Gramig, G. 2020. Hydromulching in Carrot: An Organic Weed Control Tool for Direct Seeded Crops
Rylander, H., A. Rangarajan, R. Maher, B. Caldwell, A. Butler-Jones. 2018. Reusable Black Tarps Suppress Weeds and Make Organic Reduced Tillage More Viable.
Mark Schonbeck, has over 35 publications, from 2009-2013. They include general planning and strategizing and specifics on cover crops, tarps, synthetic mulches, reduced till, no-till, weed ID, and specific crops (cucurbits) and weeds (amaranths and nutsedges).
Vern Grubinger, and M.J. Else have a series of 20 video clips on various tractor tools including a flame weeder, for weed management, 2009.
Video Clips: https://www.youtube.com/c/eorganic Click on Playlists, and whittle down your top picks from 795 videos. (The “Weed Em and Reap” title has been taken over a goat farm, so avoid searching for that)
Curran, W., and M. Ryan. 2010. Using Cover Crops to Suppress Weeds in Northeast U.S.Farming Systems.
Gallandt, E. 2012. Cultivation and Seedbank Management for Improved Weed Control Webinar.
In August, I wrote about nutsedges, weeds with three methods of reproducion; in July, Pigweeds (amaranths),warm weather annuals that put out seeds in a “Big Bang” as Chuck Mohler describes in Manage Weeds on Your Farm. In June, I wrote about docks, tap-rooted stationary perennials that are best tackled early in life; in May, galinsoga, a warm weather annual that dribbles out seeds from a young age.
This month is the turn of late summer weeds, the ones that only really get going after a long period of warm or hot weather. Here I will feature Purslane, Velvetleaf, Flower of an hour, Horsenettle, Fall panicum and Johnsongrass,
Identifying Late Summer Weeds
Virginia Tech has a very good weed ID siteand links to similar sites in some other states.
Common purslane (Portulaca oleracea) is an edible, succulent, drought-tolerant summer annual weed which grows in sprawling mats and can compete severely with young or low-growing crops. The succulent stems and leaves store water enabling the plants to surviving drought. It grows during the hottest time of year, with seed germination occurring when the soil temperature exceeds 77°F (25°C) with an optimal temperature of 86°F (30°C).
Common purslane has red fleshy stems with over 90% water content, succulent shiny oval leaves and tiny yellow flowers. It produces tiny (1mm), black, shiny, oval seeds that can remain viable in the soil for 20-40 years! Plants can produce viable seeds as soon as three weeks after emergence, with each plant capable of producing over 200,000 seeds. These traits, combined with its worldwide distribution (over 40 ecotypes,) make it the world’s ninth worst weed.
Common Purslane. Photo Virginia Tech Weed ID
Common purslane can become a major weed in over 50 crops, especially lettuce, tomato and pepper, and in row crops such as cotton and sugar beet. It is also a common weed in lawns and flower beds.
It is hard to control by hoeing, as whole plants and pieces re-root easily, if left lying on the soil. It is best hand-pulled and removed, or laid on top of dry mulch.
There are some domesticated varieties of purslane grown as a salad green. The common type is completely edible. But if keeping plants as a food crop, be warned not to let them go to seed! (New Zealand spinach is a succulent crop plant with similar seeding issues.)
Common purslane has many beneficial attributes. It is used widely for food for people and livestock. The leaves and stems can be eaten as salad, boiled or pickled. Purslane has a salty, slightly acidic taste some find similar to spinach.
It is a rich source of omega-3 fatty acids, (which support heart health), beta-carotene, (a precursor of vitamin A), and vitamin C, and antioxidants.
It has medicinal value for its anti-inflammatory and diuretic properties, and can soothe the skin and treat wounds.
It has also been shown to be an effective remediating plant to desalinate high-salt soils.
The origin of this weed is unknown, but it may have originated in northern Africa or western Asia. It was present in America in pre-Columbian times and in Italy during the Roman Age, where two sub-species were discovered during archaeological excavations.
Information and photo from Nature’s Weedy Gift? By Rakesh Chandran, WVU. (Not organic)
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Velvetleaf with Fall Panicum grass in the background. Photo Virginia Tech
AKA buttonweed and piemaker. This is a summer annual growing up to 7′ (2.1m) tall. The large hairy heart-shaped leaves can be up to 6″ (15cm) long, beautiful to the eye, but foul-smelling if crushed. The hairiness of the stems and leaves starts from emergence, with the seedlings having one round cotyledon and one heart shaped leaf. The yellow-gold flowers grow on short branches from the alternate leaf axils. They have 5 petals and are 0.5-1 inch (1-2.5cm) in diameter. Seed pods are round, slightly hairy, and can resemble shortened okra pods. The tap roots can grow quite large.
Aka rose mallow, Venice mallow, Shoo-fly, Bladder ketmia and modesty. On our farm, this weed shows up most often in the watermelon patch. It takes the same kind of conditions as watermelon in terms of temperature and days to maturity. The leaves and sprawling growth habit of this weed even somewhat resemble watermelon plants.
Flower of an hour. Photo Peter M Dziuk https://www.minnesotawildflowers.info/flower/flower-of-an-hour
The 5-petalled flowers are white or pale yellow with a purple throat, and grow from the leaf axils. The five sepals form a bladder with green veins. The fruits, if you let them happen, are round, hairy capsules
These thorny perennial nightshades are not particularly tall, but their extensive thick white rhizomes contribute to a high success rate in taking over spaces. The white star-shaped flowers are typical nightshade types (compare with potatoes and tomatoes), and the fruits are yellow globes containing 40-70 flat round orangish seeds.
Horsenettle. Photo Virginia Tech
They emerge in May here and do best in dry sandy soils, and in perennial or long-term crops. No-till practices encourage this weed.
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Photo: Fall panicum from Iowa State Integrated Crop Management
A tall summer annual grass, reaching heights of 4 ft (1.2m). The stems are often angled at the nodes, creating in ‘zig-zag’ growth habit. The seedhead is a large (16″/40cm), fanning panicle. Each spikelet produces only one seed.
Fall panicum tends to grow in cultivated areas and disrupted areas. The fibrous roots can be hard to pull, and then hard to dry out to prevent re-rooting.
Seedlings of green foxtail are similar to fall panicum in that they both have hairy ligules and lack hairs on leaf sheaths and blades. The margins of green foxtail sheaths have hairs, unlike those of fall panicum.
Fall panicum emerges later than the foxtails and this can provide the crop a head start.
This is a very large perennial clumping grass with roots like small bamboo. It can grow to a height of 6-7ft (2-2.3m). The large, loose, red-brown panicle flower heads appear May-August. It can spread via the rhizomes or the seeds. It does not tolerate repeated close mowing (Aha! The Achilles tendon!). It is especially a pest in perennial crops and no-till or reduced-till systems.
Mark Schonbeck has a lot of good info on the eOrganic site. His Principles of Sustainable Weed Management in Organic Cropping Systems, lists 12 steps for tackling weeds on organic farms, set out using the Biointensive IPM method (starting with least widely harmful strategies, and only if needed moving to the more specific control methods).
Here I have customized the steps as I see them applying to late summer weeds:
Pre-season Planning
Step 1 – Know your weeds, be sure you recognize them. Extension agents can help.
Step 2 – Plan cropping systems to minimize opportunities for late summer weeds. Include early and late cool season vegetables in rotation and vigorous summer cover crops (I love sorghum-sudangrass!) Use buckwheat or soy for short summer gaps between crops.
Step 3 –Choose row spacing based on the cultivation equipment you plan to use.
Preventive (Cultural) Practices
Step 4 – Design your crop rotation with food crops that mature at different times of year following each other.
Step 5 – Grow vigorous, competitive crops. Adjust row and in-row spacings to help the crop canopy close sooner, but don’t overcrowd your crops, as this reduces total yield, and can encourage fungal diseases. Potatoes, sweet potatoes, melons, winter squash and pumpkins all cover the ground, leaving little space for weeds. Over-winter crops like garlic and potato onions, get harvested when the late summer weeds might be starting to germinate. Be sure to sow a cover crop after allium harvests, leaving no opportunity for late summer weeds. Use drip irrigation to water only the rows of crops, not the weeds in between.
Step 6 – Put the weeds out of work – grow cover crops. This point has already been mentioned in the earlier steps.
Step 7 – Manage the weed seedbank – minimize “deposits” and maximize “withdrawals.” Mow before weeds set seed. Pull purslane, horsenettle (carefully); hoe flower of an hour and velvet leaf before they get and tough; till (repeatedly as needed) to kill the grass weeds.
Control Tactics
Step 8 – Knock the weeds out at critical times. See Manage Weeds on Your Farm.
If possible, follow multiple tilling with solarization while the weather is still hot. Organic mulches will not stop Johnsongrass or horsenettle. Solarize with clear or green polyethylene for several summer weeks. In the Southeast, clear IR plastic works best for solarizing, and heats down to a depth of 4″ (10 cm).
Step 9 – Use biological processes to enhance weed control. Not sure how to apply that idea for late summer weeds.
Step 10 – Bring existing weeds under control before planting weed-sensitive crops.
Enhancing and Fine-Tuning the Weed Management Strategy
Step 11 – Observe your weeds, and adapt practices accordingly. Make a weed logbook. Keep notes and photos of your weed management decisions and results, and avoid making the same mistake two years running.
Step 12 – Experiment and keep up with new developments in organic weed management. There are some mycorrhizal fungi that benefit most food crops, but are mildly parasitic to purslane.
Secondary Troublesome Weeds in September in Central Virginia
Flower heads of purple (left) and yellow (right) nut sedges. Photo Mississippi State U
In July, I wrote about Pigweeds (amaranths), warm weather annuals that put out seeds in a “Big Bang” as Chuck Mohler describes in Manage Weeds on Your Farm. In June, I wrote about docks, tap-rooted stationary perennials that are best tackled early in life. In May, I wrote about galinsoga, a warm weather annual that dribbles out seeds from a young age.
This month is the turn of nutsedges, “wandering” grass-like perennials that form extensive networks of rhizomes and tubers. Rhizomes are continuously growing horizontal underground stems that put out lateral shoots (popping up above ground) and adventitious roots at intervals. Adventitious roots are ones that grow from the stem, or the leaves, or from underground structures such as rhizomes, that are not roots. Tubers are thickened underground parts of stems or rhizomes, that can grow into new plants. Think of a potato growing on the buried stem of a potato plant.
Nutsedge is also known as nutgrass, cocograss, and cocosedge. Nutsedges are considered among the ten worst weeds of the US, and one of the worst 25 weeds globally.
Identifying Nutsedges
Here’s a helpful ID rhyme:
‘Sedges have edges, rushes are round, grasses have knees that bend to the ground. ‘
The ‘knees’ of grasses are joint-like nodes found along the hollow round stems. The stems of sedges and rushes are solid. The stems of rushes are round, while those of sedges are triangular, with three edges.
Mature nutsedge plants are about 6″-18″ (15-45 cm) tall, growing in bunches. The leaves are somewhat stiff and shiny. Leaves emerge in groups of three, around the triangular base of the plant. Flower stems are usually taller than the leaves, with spikes of flowers radiating from the top of the stem. Rhizomes are white, or brown with white bands. Tubers are initially white, maturing to brown, ridged “nuts”.
Species of Nutsedge
Yellow nutsedge growing among sweet potatoes. Photo Joey Williamson, Clemson University
Yellow Nutsedge, Cyperus esculentus: Yellow nutsedge has bright green to yellow-green leaves, dull yellowish flower heads of clustered “bottle-brush” spikelets. Tubers are borne singly at the end of each short rhizome. Yellow nutsedge is usually taller than the purple one. It is a bit easier to eradicate than purple nutsedge, as there are fewer tubers, and they are usually found in the top 6″ (15 cm) of the soil. Late spring or early summer deep tillage may be enough to kill off lesser infestations. This could be in spring-planted row crops. Dense plantings of food crops with abundant canopies may provide sufficient control for one season. Yellow nutsedge tubers and tuber extracts are allelopathic to crops.
Purple Nutsedge, Cyperus rotundus: Purple nutsedge has dark green leaves, purple-brown flowerheads and chains of tubers on the rhizomes. The flowers are less noticeable than the spikey yellow nutsedge ones. It is highly competitive and is more common in the Southern US states. Purple nutsedge has slightly weaker shoots, less able to penetrate 6″ (15 cm) thick organic mulch than yellow nutsedge.
No More Sedges!
Sedges can reproduce by three methods: seeds, rhizomes and tubers. Controlling sedges takes persistence.
I once discovered a colleague harvesting bottlebrush seed heads of yellow nutsedge for winter flower arrangements. (He came from a place where nutsedge does not grow.) I was horrified and tried to dissuade him, imagining him spreading nutsedge across Virginia. I later learned from Manage Weeds on Your Farm. that purple nutsedge seeds are frequently non-viable, but in light at 95°F (35°C), nearly all yellow nutsedge seeds will germinate. About 90% of yellow nutsedge populations produce no seeds, because they are part of a single clone. In field conditions, seedlings are very rare.
Yellow nutsedge rhizomes. Photo eOrganic
The rhizomes of a single nutsedge plant can form a dense mat 3′-6′ (1-2 m) across in a single season. The rhizomes provide substantial food reserves, making eradication challenging. Yellow nutsedge rhizomes produce small pea-sized tubers at their far ends, and a single plant can produce more than 1,000 tubers in a single growing season. Most of the tubers are found in the top 6″ (15 cm) of soil, and can overwinter in a dormant form if they don’t sprout. They can remain viable in the soil for more than 10 years.
Tiger Nuts aka chufa nuts aka nut sedge tubers.
The mature tubers, known as chufa, are edible, chewy and sweet. They are sold as “Tiger Nuts” and marketed as a “superfood”! I don’t recommend growing them for food. (Try peanuts instead, as they are not invasive in temperate climates.) Like potato tubers, chufa nuts have multiple buds. If the first one to sprout (the one furthest from the mother plant) dies, the next one will sprout. Their optimal sprouting temperature is 77–95°F (25-35°C), and little sprouting occurs below 50–59°F (10-15°C).
According to Manage Weeds on Your Farm, “A single [purple nutsedge] tuber can produce 99 tubers in 90 days. A tuber planted in late March produced a clone roughly 15 feet in diameter in one year, with shoots forming a nearly continuous sod in the occupied area. In a similar study, a single tuber produced a patch 238 square feet in area in 60 weeks. Stands of purple nutsedge grown from well-spaced tubers produced 1,000–3,000 tubers per square yard within 1.5–2 years.”
Nutsedge Life Cycle and Vulnerability
This warm-weather perennial weed typically emerges in early May, or whenever frosts are past. It grows actively during the hot summer months and starts to produce tubers in July. Plants can survive a week or more of light frosts, but quickly die at 23°F (-5°C) or less. Typically, long days promote vegetative growth; shortening days (less than 14 hours) promote tuber formation.
Yellow nutsedge foliage. Photo Antonio DiTommaso, Cornell
Nutsedges thrive in damp soil, and tolerate flooding, so improving drainage could help in the future. They seem to do best at pH 3.5–7, but also thrive at pH 8.7 or higher, so check your pH. Drought does not kill them, merely stops them growing. Nutsedges use photosynthetic pathway C4. Purple nutsedge thrives with high nitrogen, so avoid over-fertilizing crops or the nutsedges will grow faster, reducing the crop yield. Yellow nutsedge is relatively unresponsive to soil fertility.
Close mowing three times per week greatly reduces the spread, and seed and tuber formation, but plants could still produce 13’–19′ (4-6 m) of rhizomes and 59–103 tubers per plant in about four months. Germinated tubers can produce plants with flowers and more tubers in as little as three weeks.
Yellow nutsedge sprouting tuber. Photo Randall Prostak, U Mass
Early-mid August is a good time to tackle sedges, because uprooted plants die on the surface in hot weather (although multiple cultivations will be needed for eradication). Also the tubers will not yet have reached maturity. This process can involve taking an area out of production during the summer months, perhaps for two hot seasons. Winter food crops are still entirely possible.
Late spring or early summer when the sedges are emerging, is also a good time to tackle them, if you can find the time, as new tubers will not yet have formed.
Here I have customized the steps as I see them fitting nutsedge:
Pre-season Planning
Step 1 – Know your weeds, be sure you recognize nutsedges. Extension agents can help.
Step 2 – Plan cropping systems to minimize opportunities for nutsedges. Include early and late cool season vegetables and vigorous summer cover crops (I love sorghum-sudangrass!) Use buckwheat or soy for short summer gaps between crops.
Step 3 –Choose row spacing based on the cultivation equipment you plan to use. Don’t make false economies on hoes! Buy scuffle hoes the right width for each of your row spacings. Wheel hoe blades likewise.
Preventive (Cultural) Practices
Step 4 – Design your crop rotation with food crops that mature at different times of year following each other.
Summer-planted fall potatoes quickly cover the ground. Photo twin oaks Community
Step 5 – Grow vigorous, competitive crops. Adjust row and in-row spacings to help the crop canopy close sooner, but don’t overcrowd your crops, as this reduces total yield, and can encourage fungal diseases. Potatoes, sweet potatoes, melons, winter squash and pumpkins all cover the ground, leaving little space for weeds. Avoid planting slow-growing or skinny-leaved crops like garlic, onions, carrots in nutsedge-infested areas. Use drip irrigation to water only the rows of crops, not the weeds in between. Don’t over-water, given that nutsedge thrives in damp soil.
Step 6 – Put the weeds out of work – grow cover crops. This point has already been mentioned in the earlier steps.
Step 7 – Manage the weed seedbank – minimize “deposits” and maximize “withdrawals.” Not so important for nutsedge seeds, but this applies also to tubers and rhizomes.
Control Tactics
Step 8 – Knock the nutsedge out at critical times (August).
Till or dig deep enough to get below all the rhizomes. Rake the pieces lying on the surface and remove them. We take such things to the driveway to dry out and get run over. Each fragment left in the soil starts to grow, and once the revived plant has four or more new leaves, it can replenish the rhizome by photosynthesis, so tilling or digging may need to be repeated every 2-3 weeks during the time of fastest growth, whenever you see new 3-leaved growths. Tubers separated from the rhizomes will die in the top few inches of hot dry soil in about 8 days according to Manage Weeds on Your Farm.
If possible, follow multiple tilling with solarization while the weather is still hot. Organic mulches will not stop nutsedge, which has very sharp points. Yellow nutsedge shoots are blunted by heating under thin clear plastic. Thick plastic, opaque or clear, can suppress yellow nutsedge.
A bed of young growing turnips. Turnips are a good choice for biofumigating prior to solarizing. Photo Pam Dawling
As an alternative to tilling every three weeks from March to August, you can solarize with clear or green polyethylene for the whole period, perhaps after a spring turnip or radish crop to biofumigate the soil. Black plastic mulches will warm the soil and encourage nutsedge growth, which can then get cooked in the high temperatures under the plastic. In the Southeast, clear IR plastic works best, and heats down to a depth of 4″ (10 cm). Purple nutsedge is significantly reduced by 6” (15 cm) thick organic mulches, but yellow nutsedge is not.
Exhaust the sedges, or reduce the numbers to few enough to hand-pull them. Expect to persist with eradication attempts for two years or more.
Step 9 – Use biological processes to enhance weed control. Mycorrhizal fungi decrease nutsedge productivity. Sweet potatoes strongly inhibit yellow nutsedge, so that is worth trying. Hogs can clear 1 acre per day at a stocking rate of 24-30 pigs per acre. Chickens at 1 bird per 125 sq ft (11.6 sq m) can clear a bad infestation in two years, provided they graze uniformly (not sure how you ensure that!). Geese at 32 birds per acre can do the same, and the second year can use a lower stocking rate.
Step 10 – Bring existing weeds under control before planting weed-sensitive crops.
Enhancing and Fine-Tuning the Weed Management Strategy
Step 11 – Observe your weeds, and adapt practices accordingly. Make a weed logbook. Keep notes and photos of your weed management decisions and results, and avoid making the same mistake two years running. Finding lots of invasive wandering perennials such as nutsedges suggests you’d benefit from increasing your tillage.
Step 12 – Experiment and keep up with new developments in organic weed management, such as new bioherbicides to tackle nutsedge. There are some mycorrhizal fungi that benefit most food crops, but are mildly parasitic to nutsedges and to amaranths, chenopods, buckwheat and purslane.
Our sweet potato plot after the vines have run. A great choice for battling light infestations of nutsedge. Credit Kathryn Simmons
Food Crops After Nutsedge Management
After a summer treatment, grow a heavily mulched or very vigorous large-canopy fall or winter crop. Cereal cover crops are a good choice. Next summer you could grow sweet potatoes, which inhibit nutsedge growth, but be aware that the yield can be reduced by any surviving nutsedge. Green beans, cabbage and other fast-growing, ground covering crops will do better than slower, more sparse crops. Avoid onions, garlic, okra after nutsedge.
Secondary Troublesome Weeds in August in Central Virginia
Mugwort and Bermuda grass (wiregrass) Photo Pam Dawling
In May, I wrote about galinsoga, a warm weather annual that dribbles out seeds from an young age. In June, I wrote about docks, tap-rooted perennials that are best tackled early in life. This month is the turn of pigweeds, warm weather annuals that put out seeds in a “Big Bang” as Chuck Mohler describes in Manage Weeds on Your Farm. Pigweeds are fast-growing, tall, erect-to-bushy weeds that respond to high levels of nutrients as found in gardens and crop fields. Like corn, they use the C4 photosynthetic pathway, which means they thrive in high temperatures and high levels of light. They avoid getting shaded by growing fast, and they tolerate drought. Their vulnerability is that they do not produce seeds until they have been growing for some time and have reached a noticeable height.
Green Amaranth/Calaloo, grown for cooking greens. Photo Baker Creek Seeds
Pigweeds are amaranths, a family that includes valuable food crops used for grains and greens, as well as dreaded weeds such as Palmer Amaranth, Waterhemp and Spiny Amaranth. Pigweeds are frost-tender, but if you have a long enough frost-free period, one plant can produce over 200,000 seeds.
Species of pigweeds
Mark Schonbeck has written a profile of pigweeds on the eOrganic site. He provides a list of eight unwelcomed pigweed species:
Silver Queen sweet corn with wilting pulled pigweed amaranth. Corn is a C4 crop, amarnath (pigweed) a C4 weed. Photo Kathryn Simmons.
Our experience with redroot pigweed in sweet corn
When I first encountered pigweed, I was told they were more-or-less impossible to deal with. Once I learned from Manage Weeds on Your Farm that, as tender annuals, they die with the frost, and as Big Bang weeds, they produce no seeds during most of their growth (unlike galinsoga!), I started a program of pulling them in our sweet corn patches. We used to grow a lot of sweet corn, and this tall crop, taking about ten weeks to mature the harvest, is a good habitat for pigweeds. We cultivate our sweet corn two weeks and four weeks after sowing, then don’t come back until the corn is ripe. This is an excellent window for pigweed to mature in! We started pulling the huge pigweeds each time we harvested corn. Inevitably, the weeds were right next to the corn plants, where our hoeing had failed to dislodge them. We found that if we put one foot against the base of the corn stalk and grasped the pigweed firmly and pulled up, we could usually tug them out. This won’t work if your soil is a tight clay, and if the pigweed breaks, the stem will branch and regrow. Most times, we harvest a patch of corn for two weeks and then disk or till it under. Usually we are turning the crop and weeds under before the regrown pigweed has had a chance to set seed.
“Economic thresholds (weed levels that cause a 5% yield loss) for pigweeds emerging with corn and soybean crops have been estimated as low as 0.2–0.5 plants per 10 square feet, and 2–4 plants per 10 square feet for weeds emerging after crop seedlings have several leaves (Costea et al., 2004). In Ontario, redroot pigweed that emerged in corn at the 3–5-leaf stage at populations of 0.5–2.5 weeds per foot of row reduced yields 10–30%, whereas pigweed emerging at the 7-leaf stage had little effect (Knezvic et al., 1994)”
Our experience was that our corn yields were good, and we had found a successful method to manage the levels of pigweed over several years. We were cultivating between the rows and undersowing with soy at 4 weeks after sowing the corn, so the pigweeds growing were only those very close to the corn stalks. I do picture that an understory of pigweed would have a serious effect.
Spiny Amaranth
Spiny amaranth – a weed to exterminate by careful pulling. Photo Pam Dawling
Spiny amaranth has been designated the world’s 15th worst agricultural weed. We have twice eliminated spiny amaranth from our gardens for a number of years, and then had it return. The seeds can remain viable in the soil and regrow when they are exposed to light. Although not as tall-growing as redroot pigweed, spiny amaranth has other ways of succeeding against those who would remove it from their crops: The nasty 0.5” (13 mm) spines (borne in opposing pairs at each leaf node) are not very visible among the branches, and are close enough together to make grasping the stem difficult.
The leaves of spiny amaranth are a darker green than redroot pigweed and have a V-shaped mark in a different color. Spiny amaranths can produce even more seeds than redroot pigweed: 235,000 each. Beware importing animal manure from other farms, and even gravel. I have seen a spiny amaranth germinate in a fairly large gravel pile brought in for road repairs.
Six methods of tackling pigweeds
Mark Schonbeck lists six methods of tackling pigweeds in organic production systems, and recommends using a combination of:
Cultivation, flame weeding, and manual removal 2-3 weeks after emergence
Stale seedbed
Mulching
Crop rotations that vary timing of tillage and other operations [our sweet corn was one year in 3 or4]
Cover crops and competitive cash crops
Measures to prevent or minimize production of viable seeds
Pigweed Flea Beetle
Disonycha glabrata – Pigweed Flea Beetle. Photo from Bug Guide.net
Pigweeds even have their own striped flea beetle, Disonycha glabrata from the Chrysomelidae family. It is a large flea beetle. More the size of a striped cucumber beetle, but with a reddish thorax. It feeds on Redroot Pigweed (Amaranthus retroflexus) and other amaranths, so we never even try to grow salad amaranths as the leaves get riddles with holes. The first larval stage lasts 3.6 days, the second 2.6 days, and the third 2.9 days. It spends 13.5 days in the soil.
Another Weed Management Resource
The book Steel in the Field, available as a downloadable pdf from SARE
Dock weeds flowering and seeding in early June. Photo Pam Dawling
This is the second of my once-a-month series of posts focusing on weeds. One weed that is making itself very evident on our farm in late May and early June is the dock. We have both the broadleaf dock, Rumex obtusifolius L. and the narrow-leaved or curly dock, Rumex crispus L. Docks are in the buckwheat family.
Docks are tap-rooted perennial weeds, requiring different approaches to last month’s weed, the fast-seeding annual galinsoga.
Cover of Manage Weeds on Your Farm SARE
See the excellent information on docks in the book, Manage Weeds on Your Farm: A Guide to Ecological Strategies, By Charles Mohler, Antonio DiTommaso and John Teasdale. Click the link to read my review. It’s a book worth having on your shelf and it’s also available online from SARE It explains how to tackle various types of weeds in an ecological way and then profiles many individual weeds. With good clear photos of weeds at various stages of their lifecycle. Here you can find out what dock seedlings look like, and go and hoe them out before they get too big.
When dock seeds germinate they first develop a rosette of leaves close to the ground. The rosette grows quite large (leaves can be 12″ by 6″ with broad-leafed docks, 12″ x 2.5″ for narrow-leafed docks), at which point most of us cannot simply pull the dock out as the tap root will be sturdy and long. You will need a digging fork or a shovel to get the root out. As with other tap-rooted perennial weeds, if the root breaks, the part remaining in the soil can regrow. The short, vertical underground stem that attaches to the roots regrows readily. In spring, new plants can also grow from fragments of the true root.
Broad-leafed docks have branching taproots, while the narrow-leafed docks have a single root, with almost no branches. If left to their own devices, the leaves become speckled with red and the plant puts up a tall stem with clusters of inconspicuous reddish flowers. The flowers mature into winged fruits surrounding three-sided glossy reddish seeds.
Dock as a rosette. Photo University of Maryland Extension
Docks can become established in uncultivated but fertile areas, especially along edges of pastures or areas with long-term cover crops. frequent mowing before docks get a chance to grow large can help other plants to out-compete the docks. The key is to provide enough nitrogen for your crops but not more, or the docks will suck it all up! Vigorous crops can out-compete docks for light (part of why docks do well on edges where they have no competition).
If docks get too big and have flowering heads or even seed heads, it is best to dig them out and take them away. This is a good time of year for that, before the seeds mature and scatter. If I dig just one or two docks, I put them on the driveway to dry out and get road-killed by vehicles rolling over them. If we take advantage of a day with lots of help, especially after rain when the soil is easier to dig, we take wheelbarrows and make a team sport of it, digging all the docks from one area. We have a special place under trees that we call the End of the World, where we pile noxious weeds. The shade discourages them from regrowing, as does the sheer weight of the weeds we pile up.
On a larger scale, if a whole field has become infested with dock, say a pasture that you want to convert to growing annual crops, then stronger measures are called for. Disk or plow the field in midsummer (now!), and repeat the cultivations whenever the weather is suitable for drying out fresh root pieces that will get brought to the surface. I would not normally advocate repeated tillage and leaving soil bare, but annual crops are no match for established perennial weeds.
Narrowleaf or curly dock with a stem of still-green flowers. Photo University of Kentucky Dept of Plant and Soil Sciences
If you are using a rototiller, be sure to work down to a depth of four inches. If you till shallowly, you might just severe the neck from the root, allowing the dock to regrow. Run your machinery slowly and get maximum chewing-up action. When you see new shoots with 2” leaves growing, repeat the tilling. This is the stage at which the regenerated plant has extracted lots of nutrients from the root piece and has not yet paid much back. Don’t wait longer!
Winter cover crops can do a lot to suppress new dock seedlings as well as regrowths. The growth rate of docks is slow-and-steady, the opposite of galinsoga! Tackle docks before they disperse their seeds. Once shed, dock seeds are initially dormant for some months. Germination occurs at 50°F–95°F (10°C–35°C) with 68°F–77°F (20°C–25°C) optimal for fastest germination. Cooler nights and warmer days help speed germination, as does light exposure, unless filtered through overhead trees, which decreases germination. Flushes of seedlings tend to germinate in spring and fall.
Seeds of broadleaf dock can remain viable for 40 years, and those of narrowleaf dock can live in the soil as long as 80 years! But the rate of seed mortality each year is quite high. Manage Weeds on Your Farm quotes one experiment in Ontario, when less than 15% of curly dock seeds and 1% of broadleaf dock seeds survived more than one year.
Large dock weeds in early June Photo Pam Dawling
Docks that survive the winter as rosettes make new growth in spring (February to March) and flower in April and May. Seeds mature a mere 6-18 days after flowers open. If you see flowering docks, don’t delay!
Both dock species are relatively short-lived perennials, nearly all dying within 4 years. By that time, they may have produced over 240,000 seeds.
Dock leaves are edible by people and pigs, but not cattle, horses or poultry. They may be cooked like spinach and many people find them very tasty.
