Weed of the Month for May: Galinsoga

People in early spring weeding spinach that has been hooped and covered overwinter.
Photo Wren Vile

This is the first of my new monthly series of posts. All about weeds.

Sustainable (or Ecological) Weed Management: A Holistic Approach to Organic Weed Management

In the early days of organic farming, maximum use was made of frequent cultivation to kill weeds. Now we know that too-frequent cultivation risks causing soil erosion, and that each tilling or deep hoeing stirs air into the soil and leads to a burning-up of organic matter. The practice of sustainable weed management is about effectiveness – including removing weeds at their most vulnerable stage, or at the last minute before the seed pods explode – and ignoring weeds while they are doing little damage. Work smarter, not harder!

Start with restoring and maintaining balance in the ecosystem. Develop strategies for preventing weeds and for controlling the ones that pop up anyway. An obvious point is to avoid adding new kinds of weeds to any part of your fields. Remove the hitch-hikers from your socks out on the driveway, not when you notice them as you squat to transplant onions! We use our driveway as a convenient place to “roadkill” particularly bad weeds by letting them die in the sun. Beware of Trojan plant swaps!

Weeding in early June. Photo Lori Katz

Weeds are not a monolithic enemy, but a diverse cast of characters. Applying biological principles is not an attitude of war, but more like ju-jitsu, using the weaknesses of the weeds to contribute to their downfall. Develop an understanding of weeds and the different types: annual/perennial; stationary perennials/invasive perennials; cool weather/warm weather; quick-maturing/slow-maturing; and what Chuck Mohler referred to as “Big Bang” versus “Dribblers”. In this monthly blogpost series, we’ll meet various types of weeds, and develop a broader understanding of how and when to tackle each kind.

One factor to consider is how vulnerable the crop is to damage from that weed at that time. Weeds that germinate at the same time as a vegetable crop usually do not really affect the crop’s growth until they become large enough to begin competing for moisture and nutrients. These early weeds have the greatest potential for reducing crop yields if allowed to grow unchecked. We need to cultivate or otherwise control weeds before this 2- to 3-week grace period is over.

Weedy sweet corn. ideally, we would have cultivated two weeks and four weeks after sowing. Photo Bridget Aleshire

The critical period for weed control for the crop is the interval from the end of the initial grace period until the end of the minimum weed-free period, which is approximately the first third to one half of the crop’s life. For vigorous crops like tomato, squash and transplanted brassicas this is four to six weeks; less vigorous crops like onion or carrot need weed-free conditions for eight weeks or more. During that period it is essential to control weeds to prevent loss of yield.

Weeds that emerge later have less effect, and ones that emerge quite late in the crop cycle no longer affect the yield of that crop, although there are long-term reasons for removing weeds to improve future crops.

Know Your Weeds

Lettuce with weeds, easily hoed. Photo Bridget Aleshire

Learn to identify the major weeds on your farm, and any minor ones that suggest trouble later. Observe and research. Start a Weed Log with a page for each weed. Add information about your quarry’s likes and dislikes, habits and possible weak spots. Find out how long the seeds can remain viable under various conditions, and whether there are any dormancy requirements. Note down when it emerges, how soon it forms viable seed (if an annual), when the roots are easiest and hardest to remove from the soil (if a perennial), what time of year it predominates, which plots and which crops have the worst trouble with this weed. Monitor regularly throughout the year, each year. Look back over your records and see if anything you did or didn’t do seems to have made the problem worse or better.

Next think about any vulnerable points in the weed’s growth habit, life cycle, or responses to crops or weather that could provide opportunities for prevention or control. List some promising management options. Try them, record your results, decide what to continue or what to try next.

Most weeds respond well to nutrients, especially nitrogen. If you give corn too much nitrogen, even as compost, the corn productivity will max out and the weeds will use the remaining nutrients. Some crops, like carrots and onions never cast much shade at any point of their growth, so that sun-loving weeds like purslane are more likely to thrive there, but not be a problem for crops which rapidly form canopies that shade the ground.

Galinsoga – a fast growing, fast-seeding weed of cultivated soil.
Photo Wren Vile

Galinsoga

This month’s Weed Character is galinsoga, a “Seed Dribbler”, that matures seed while still quite small plants, sheds some, makes some more, and can carry on for a long seed-shedding season.

Encouraging information is that a constant percentage of the seeds that are still left from one year’s shedding dies each year. This varies widely among species – for lambsquarters it’s 31% per year in cultivated soil (only 8% in uncultivated soil). The number of seeds declines rapidly at first, but a few seeds persist for a long time.

While seeds survive better deeper in the soil, they don’t germinate better down there. Larger seeds can germinate at deeper levels than small seeds. If you are trying to bury seeds deep, use inversion tillage, don’t rely on rotavating, as seeds somehow manage to stay near the surface with rotary tilling. Chuck Mohler, author of the excellent book Manage Weeds on Your Farm, has tested this out with colored plastic beads.

We have two kinds of galinsoga: narrow-leaved and hairy. Both behave the same way. They thrive in highly fertile, freshly tilled soil, just the same as you hope your vegetable seeds will. Mostly we think about how to get rid of galinsoga (prompt hoeing or other cultivation before it flowers), or stop it germinating in the first place (mulches). Its flowers attract beneficial insects such as hoverflies, and it can be eaten by humans and livestock. Young leaves can be used in a soup or in mixed dishes. It doesn’t have a strong flavor. The plants contain flavonoids and phenolic compounds, and it has been found to have antioxidant and anti-inflammatory properties. Extracts from hairy galinsoga can coagulate blood. It is an alternate host for certain nematodes and over twenty insect pests. Hairy galinsoga is thought to have originated in Central and South America, and has become naturalized in North America and other temperate and tropical regions.

Galinsoga is a summer annual that belongs to the sunflower family (Asteraceae) and can invade vegetable gardens with dense infestations that crowd out crop plants. The secrets of galinsoga’s success are that its seeds germinate immediately they reach the soil (no dormancy period), it grows very fast, shading out other plants, it sets seed in as few as 30–40 days after emergence, and continues shedding seed as long as it is growing. It also has the knack of re-rooting if pulled and laid on the surface of the bed, if there is any moisture in the soil. Large plants seem able to transfer the water in their cells to their roots, helping re-rooting happen. Seed that is shed early in the year is capable of growing a mature plant very quickly. There can be multiple generations in one warm season. Fortunately, the seeds are short-lived, and have to be in the top 0.25″ (6mm) of the soil to germinate.

Hoe weeds while they are small and you’ll be rid of those with short-lived seeds in a few years. Galinsoga and Outredgeous lettuce.
Photo Pam Dawling

Galinsoga Identification

Hairy galinsoga (Galinsoga quadriradiata), has profuse hairs on stems and leaves. Narrow-leaved galinsoga ( Galinsoga parvifolia), is very similar, except it is not hairy and it has narrower leaves. Leaves are oval with serrated margins and distinct petioles. They are arranged opposite each other on the stems. The flowers have densely packed yellow disc florets and five tiny white ray florets, each with three scalloped teeth at the end. Seeds of hairy galinsoga germinate between 54°F-86°F (12°C-30°C) with an optimum temperature requirement of 68°F-75°F (20°C-24°C). Most of the seed germination occurs from May to June, after the last frost. It flowers abundantly from about late-May until late fall here in central Virginia. Fallen seeds can germinate immediately due to the absence of dormancy requirement. Take advantage of this phenomenon to eradicate hairy galinsoga from an infested field in three to four years by careful management.

Controls for Galinsoga

Prevention of Weed Germination

Hoeing or mechanical cultivation is effective if carried out repeatedly during the early stages of growth (before flowering). Mulches, such as thick (6-mil) black plastic, or straw, hay, leaves, woodchips over cardboard or newspaper, are effective to control galinsoga in small gardens if applied immediately after planting the crop and before the galinsoga germinates.  Tarping is the equivalent solution for larger areas.

Reduction of Weed Seeding

Grazing, or the mechanical equivalent, mowing, will take care of galinsoga in places you are not currently growing a crop. This weed is not usually found in lawns. It has no resistance to frost. Livestock will happily graze it.

Reduction of Viability of Seeds

Most weed emergence happens within two years of the seeds being shed. Not all seeds that are produced will ever get to germinate (I was very pleased to learn that seeds have many ways of not succeeding!) You can help reduce their chances, by mowing crops immediately after harvest, (to prevent more weed seed formation); then wait before tilling to allow time for seed predators to eat weed seeds that already produced. Seeds lying on or near the soil surface are more likely to deteriorate or become food for seed predators than buried seeds, so delaying tillage generally reduces the number of seeds added to the long-term seed bank. (Short-term, they may germinate!)

If they do not get eaten, dry out or rot, seeds on top of the soil are more likely to germinate than are most buried seeds, and small, short-lived seeds of weeds which have no dormancy period, such as galinsoga, will almost all die within a year or two if they are buried a few inches.

Putting it Together

Strategies include

  1. Inversion tillage such as moldboard plowing (seeds will die off deep in the soil within a year or so.)
  2. Mulching – the seeds will not germinate or be able to grow through the mulch, and will be dead by next year. Be sure to rotate the mulched crops around the farm, so that the benefits are not confined to one section;
  3. Grazing with small livestock, or harvesting galinsoga for human consumption, or mowing: especially mow as soon as the food crops are finished, if you cannot till right away.
  4. Tarping (mow first);
  5. No-till cover crops, with summer crops transplanted into the dying mulch;
  6. Stale seed bed techniques, including flaming;
  7. Plant flowers that attract beneficial insects, particularly seed-eating insects, and birds.
Front cover of manage Weeds on your Farm

Resources on Weeds

2023-2024 Conference Tips 3 – Climate Change, less usual edible plants

Carrots under shade cloth in summer.
Photo Pam Dawling

2023-2024 Conference Tips Part 3 – Climate Change, Less Usual Edible Plants

I reported earlier on good tips I got from the CFSA Conference and the VABF-SFOP Summit.  Here I’ll continue the theme.

At the VABF-SFOP Summit, I also attended workshops on Meeting the Climate Challenge with Mark Schonbeck, and Eating and Marketing the Whole Plant with Chris Smith. I’ll tell you more about those now, then move on to the Pasa Sustainable Agriculture Conference.

Meeting the Climate Challenge: Sharing Stories, Co-Creating Solutions with Mark Schonbeck

Mark’s slides and handout will be available soon on the VABF website. In our region we are experiencing hotter summer nights, which are hard on plants (and livestock, I’m sure). At 95F (35C) most crops close down completely or slow their growth. For every 1.8F (1C) in warming, 3-10% of the Organic Matter is lost (burned up) and nitrous oxide emissions may increase 18-28%. Daffodils are flowering up to 5 weeks earlier, fruit trees are budding out earlier, risking losing the fruit to freezing nights. In the spring we are getting later cold snaps below 10F (-12C) in March.

We are having a longer frost-free period, with more generations of bugs. Downy mildew of cucurbits is spreading further north than previously.

Our kale beds after heavy rain. Photo Wren Vile

In Virginia we are getting more intense and heavier rains, with more flooding. The erratic nature of the rains means we can experience flash floods, followed by droughts and wildfires. Heavy rainfall leads plants to grow shallower roots, which then die if a sudden drought follows.

Keeping living roots in the soil will increase climate resilience, as will other ways of building healthy soils, such as diversified rotations, and varied agricultural enterprises. Here’s Mark’s list of

6 Organic Principles of Soil Health:

  1. Keep the soil covered
  2. Maintain living roots
  3. Return organic residues to the soil
  4. Minimize soil disturbance
  5. Diversify crops
  6. Integrate livestock.
Teff cover crop.
Photo Wikipedia

Increasing the use of cover crops will help with 1, 2, 3 and 5. Teff can be considered as a summer cover crop in alleys between plastic mulched beds. Mixing with clover gives better soil coverage. I have not yet tried this myself. Oats/barley/peas/mustard sown in March will grow big by June, adding lots of biomass. Oats/radish/legume cover crop mix will winter-kill. Silage tarps and landscape fabrics can help hold the soil in place.

Installing terraces, berms and swales will help with water management. Installing drip irrigation will help manage droughts. Protected growing, in hoophouses or caterpillar tunnels, will help protect from many kinds of extreme weather. There are steps we can take to mitigate climate change, and more information is becoming available.

Eating and Marketing the Whole Plant with Chris Smith

Chris is the author of The Whole Okra, and part of his presentation was about the many uses of okra, beyond cooking the pods. Okra leaf chips are the latest thing he has tried. The leaves are used for soup in Nigeria. The flowers can be eaten or dried for tea. The oil from okra seeds is nutty, citrusy, a bit like olive oil, although the yield is small, at 9-20%. The oil presscake can be ground for defatted flour.

Book Edible Leaves of the Tropics by Franklin Martin, Ruth Ruberte and Laura S Meitzner

Chris showed us a remarkable book Edible Leaves of the Tropics, by Franklin Martin, Ruth Ruberte and Laura S Meitzner. Plants for a Future  has a database of 8000 plants, including edible plants.  The Book of Greens by Jenn Louis and Legume Species as Leafy Vegetables by Robert P Barrett (online) are also valuable resources on edible plants.

DIYseeds.org educational films on seed production

Go to https://www.diyseeds.org  then search for info on growing seeds.

Male squash flowers can sell at $1/flower for an 8-week season. Winter squash yields can increase if some of the early male flowers are removed! Wisteria, redbud and black locust flowers are edible. Kudzu offers many food options (eat it up!) Roots of dandelion, burdock, thistle, sassafras, daylily, dahlia, runner bean and chayote are all edible.

Soil Health, Climate Adaptation and Mitigation Planning, Rachel Schattman, Sara Keleman and Nic Cook

In February 2024, I participated in the Pasa Sustainable Agriculture Conference.  The first session I attended there was Soil Health, Climate Adaptation and Mitigation Planning, with speakers from the University of Maine Climate Science department. They reported that the NE has seen a 15% increase in Growing Degree Days since 1948, and the frost-free growing season in Maine has increased by 14 days since 1895. California has seen a 40-50 day increase in that period. In Maine the temperature changes are greater in winter than in summer. Since 2012, half of the US has shifted to the next warmer winter-hardiness zone. It is helpful to watch indicator species to determine when to plant particular crops. (See my post on Phenology). Warmer temperatures mean that the air holds more water (7% more for each C degree). This means slower storms, more storms heavier rainfall. They also experience droughts, and distinguish between agricultural drought, meteorological drought, and hydrologic drought – be sure which kind your conversations are about.

Young blueberry plant in snow. Photo Bridget Aleshire

Sea level rise is dramatic on the East coast because of past glaciation. The other main impacts they are seeing on agriculture include False Spring (fruit bud kill after a “warm snap”), winter soil erosion and rain ponding, and new pests, diseases and invasive species, warm season heat stress including crop quality deterioration, greater irrigation demands and needs for shade and ventilation (drought can decrease yields 30%), storm intensity including hail and high winds, longer power outages, soil compaction and nutrient runoff, increased rainfall leading to delayed planting and crop losses. These are all possibilities to prepare for. The silver lining is that there may be new crops we can grow, or longer seasons of familiar crops. NRCS, Extension and other resources are available. Climate-Smart Farming and Marketing is a program for farmers from Maine to South Carolina, offering financial support and technical help to farmers implementing climate-smart practices such as cover cropping, agroforestry, reduced tillage and prescribed grazing.

Prescribed grazing is the intentional use of ruminant animals (hoofed herbivores such as cows, sheep, and goats) on the landscape. Unlike conventional grazing, prescribed grazing utilizes a grazing plan that dictates the location and duration of graze periods. This plan is informed by the ecology of the grazing area.” (Community Environmental Council).

Garlic beds next to rowcovered broccoli beds, under a stormy sky.
Photo Wren Vile

We were helped through an 8-stage planning process:

  1. Risk Assessment (prioritizing which aspect of climate change to deal with first). Heavier rains, then high temperatures, wildfire and smoke, plant diseases.
  2. Vulnerability (looking at your system, climate, location, and seasonal time period). Consider both Exposure to the risk and your farm’s Adaptive Capacity.
  3. Option ID. Consider all of small, medium large and total transformation of your farming. Divide your options up into 4 quadrants on axes of cheap-expensive, difficult-easy; low Greenhouse Gas-high GHG, reducing risk-increasing risk; low impact-high impact, quick to install-takes a long time.
  4. Evaluate tradeoffs (financial, ecological, social). Rank your options and select one that meets as many of your priorities as possible.
  5. Try to meet several goals with one solution. Consider seeking advice or funding.
  6. Monitoring and assessment. How will you measure the improvements?
  7. Revising/tweaking. Reflect and assess. Consider success at each stage.
  8. Share what you learned. Don’t expect perfection, or that others will expect that from you.

Next followed a section on funding. Currently there is lots in Inflation Reduction Act coffers for efficiency increases, renewable energy, conservation practices. Try REAP (Rural Energy for America Program), USDA, NRCS, Rural Development Office for your state, SARE funding for experimentation and trials, state agriculture departments, advocacy organizations, regional non-profits, Chesapeake Bay Trust, Farmer Resource Network, county grants, Beginner Farmer grants, grants for historically under-served farmers, Ambrook Accounting software for American farms..

Take a buddy with you to the offices!

Farmer Resource Network

Cover Crops for May: Buckwheat

Buckwheat in flower in September.
Photo Pam Dawling

This is the first of a monthly series on cover crops, which will take us through a whole year, to April 2024.

Why Grow Cover Crops?

<a title=”USDA, Public domain, via Wikimedia Commons” href=”https://commons.wikimedia.org/wiki/File:Soil_food_webUSDA.jpg”><img width=”512″ alt=”Soil food webUSDA” src=”https://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Soil_food_webUSDA.jpg/512px-Soil_food_webUSDA.jpg”></a>

See my post Cover Crops in Summer.

  • Cover crops suppress weeds and provide a boost to soil organic matter.
  • Keep live roots in the ground as much of the time as possible, to feed the microorganisms in the Soil Food Web.
  • Here is a diagram of the Soil Food Web: https://upload.wikimedia.org/wikipedia/commons/8/89/Soil_food_webUSDA.jpg
  • Roots anchor the soil, preventing erosion in heavy rains.
  • Dead roots also have a role, providing drainage channels in the soil and letting air in deeper.
  • Adding organic matter to the soil is a way of sequestering carbon, as well as providing nutrients for your crops.
  • Deep-rooted cover crops draw up nutrients, bringing them up where crop plants can access them.
  • Leguminous cover crops provide nitrogen, saving imports of organic fertilizers or a big compost-making operation.
  • Too often, gardeners grow cover crop only in the off-season, to protect the soil in winter, and assume it’s not a summer option. But it is, and planting summer cover crops provides many benefits.

Focus Cover Crop for May: Buckwheat

A bed of young buckwheat with a cosmos plant to attract beneficial insects. Photo Pam Dawling

I have a blog post Buckwheat, a wonderful summer cover crop, introducing an article I wrote for Growing for Market magazine. See that post for basic details I mostly won’t repeat here.

Buckwheat (Fagopyron esculentum) is a fast-growing warm-season broadleaf annual that is a very useful cover crop. Its special strengths are in weed-suppression, attracting beneficial insects, improving the soil tilth (aggregate structure) with its fibrous roots, and extracting potassium, calcium and phosphorus from the soil to the benefit of following crops. Buckwheat is almost three times as good as barley in scavenging phosphorus, and more than ten times better than rye (a poor phosphorus scavenger). Because buckwheat is not related to any of the common food crops, it is simple to include in rotations.

Buckwheat can be sown up from your last frost up to 35 days before first fall frost. Buckwheat can close its canopy in just two weeks, preventing the soil baking in summer conditions. Because it matures quickly, and self-sows, it can be used in several successions with tilling between, to suppress some perennial weeds.

Flowering buckwheat in September.
Photo Pam Dawling

Buckwheat can do fairly well on poor soils, is tolerant of a range of soil pH and is an easy crop to deal with manually or with small-scale equipment. Even mature buckwheat plants are easy to deal with using manual or small-scale equipment. You can just pull up the plants by hand, or use a hoe or scythe to slice them off at the soil line. You can chop them into the soil, or gather them up and compost them. Or you can use a no-till method, let the dead plants die into a surface mulch and plant through them.

Buckwheat yields only a couple of tons per acre, but does it in only six to eight weeks. If you want to increase the (admittedly sparse) biomass, cut down buckwheat just before it reaches 25% bloom, to a height above the lowest leaf node. Buckwheat will regrow rapidly and you may even be able to make a second cutting.

Buckwheat also makes good food for poultry or rabbits, and chickens love the seeds. It does not provide good forage for larger livestock.

Beds of young buckwheat.
Photo Bridget Aleshire

Barbara Pleasant, in her 2009 article Cover Crops, described Rhizodeposition as a special advantage of using cover crops. Many plants release sugars and other substances through their root hairs into the soil. They are solar-powered pumps, sending energy down into the soil, causing the root tips to host colonies of useful microorganisms. As the roots move deeper, the microbes follow. With vigorous winter cover crop plants, like oats or rye, this process goes on down to 6 feet (much more deeply than you should dig). Buckwheat doesn’t go very deeply at all, but it can be working for you, which is much better than leaving the soil empty and drying out.

Buckwheat in flower in June. Photo Pam Dawling

Buckwheat Resources

Secondary Cover Crops for May

Soy, mustard, sunn hemp, southern peas are all also good summer cover crops, and I will say more about them in the next few months. See Cover Crops in Summer.

Sunnhemp cover crop at Nourishing Acres Farm, NC.
Photo Pam Dawling

Sunn hemp, a nitrogen-fixing legume from the tropics, can grow as tall as 9’ (2.7 m) in a few months. Sow sunn hemp from a week after your sweet corn sowing date, up to 9 weeks before your first fall frost, which will kill it. It tolerates a wide range of soils (but not if waterlogged). Plant inoculated seed (use the same inoculant as for southern peas) 1” (2.5 cm) deep, with seeds 1.5” (4 cm) apart in the row, and with rows 6” (15 cm) apart. Sowing densely (as with all cover crops) will work better to smother the weeds.

If you sow sunn hemp in a summer gap between spring and fall vegetable crops, it will provide a nitrogen boost for the fall crop, because it is a legume. In dense plantings, it can fix more than 120 lbs (54 kg) of nitrogen and 12 pounds of biomass per 100 sq ft (0.56 kg/sq m). 60 days after sowing, the stems thicken and become fibrous and high in cellulose; cutting at this stage produces long-lasting mulches that increase soil carbon. If you cut the crop back at a younger stage, this will stimulate branching (more biomass) and more root penetration (better drainage).

Sunn hemp cover crop at Nourishing Acres Farm, NC
Photo Pam Dawling

We have taken to sowing sunn hemp as a summer cover crop in our hoophouse, and lopping it periodically with hedge shears to an ergonomic elbow height. This is because we don’t want it to shade crop plants further back (north). The fallen tops make a nice “forest floor” carbonaceous mulch.

Mustard we don’t grow as cover crops, although I do have experience of growing it in England, where it is one of the favorite cover crops for short crop gaps, or in preparing areas reclaimed from pasture or lawn. We have too many harlequin bugs, and we hope to break their lifecycle by having a summer month without any visible brassicas. (We do often have fall brassica seedlings growing under insect netting.) Also, our “crop portfolio” has plenty of brassicas already, and we’d rather have a better rotation, with brassicas less often.

Mustards can decrease weeds, or certain pest nematodes, if you grow the right kind.

Soybeans as a cover crop
Photo agcrops.osu.edu

Soybeans are a great summer cover crop and they are also a legume, so they add nitrogen to the soil. They have good shade tolerance and tolerance to foot traffic (that is, people harvesting crops on either side. Because of this, we like using soy to undersow in sweet corn.

Southern peas are another warm weather cover crop option. They are also a legume, and so will add nitrogen to the soil. Iron and Clay is the sprawl variety best known for cover crop use, but other varieties also work.

Iron and Clay southern peas flowering in September. Photo Pam Dawling

Cover Crop Planning

My book Sustainable Market Farming has a chapter on cover crops and 9 pages of charts about particular options.

The book Managing Cover Crops Profitably (third edition) from the Sustainable Agriculture Research & Education Program (SARE), is the best book I know on the subject. You buy the book for $19 or download it as a free PDF from SARE.

See Harvey Ussery  Four Outstanding Cover Crops for Summer.