Workhorse Crops for March

 

Flats of transplants in our cold frame ready for transplanting.
Pam Dawling

We’ve just got a few months left in my monthly series of 14 Workhorse Crops (asparagus, beans, cabbage, carrots, chard, collards/kale, garlic, potatoes, sweet corn, sweet potatoes, tomatoes, watermelons, winter squash, zucchini/summer squash). These crops are reliable and productive under a range of weather conditions. You can use the search box to find other posts in the series, such as February.

Spring is on the way! Many more crops to plant this month! Our average last frost (over the past 14 years) here in central Virginia is April 29. We reach 11 hours of daylight on February 20, and we and everyone else will reach 12 hours on the March 20 Equinox. It’s all go!

In our hoophouse we are clearing bolting crops and transplanting spinach (the “Racehorse” of this series) wherever we have space along the edges of the beds. The tomatoes go in in March and squash, cucumbers, and peppers in April. Those crops will occupy the centers of the beds, before taking over the whole width. Our greenhouse is filling up with transplants.

Workhorse Crops to Plant in March

Young spring cabbage with a hay mulch. Wren VIle
Cabbage

We transplant our early cabbage around March 6. We had trouble with mice in the greenhouse in early February and lost quite a few seedlings. We also made the mistake of using seed that was too old. So we will have only one bed of early cabbage this year, not two. We did try to make up for the losses by resowing fast-maturing varieties, but we still ended up short. We like Farao (60d) and Early Jersey Wakefield (63d). Both numbers are seed to harvest. Subtract 20 days if counting from transplanting to maturity. We will cover the bed with thick rowcover for the first few weeks after transplanting.

Carrots
Newly emerged carrots with indicator beets.
Photo Kathryn Simmons

We sow carrots in mid-March, and again at the end of March. The mid-March sowing takes from 9-19 days to germinate, depending in on the soil temperature. The end of March sowing takes 9-12 days. We sow a few Indicator Beets at the beginning of the bed. Beets germinate one day sooner than carrots at almost any temperature. When we see the red loops of the beet stems emerging, we know it’s the day to flame weed the carrots.

Chard

We sow chard (and leaf beet, the type of chard closest to spinach) on March 24, but you can start earlier if you want earlier harvests. Chard seed will germinate from 41°F (5°C) to 95°F (35°C), and the best temperature is 86°F (30°C), when it needs only 4 days. Our goal is to use chard as our main summer leafy green after the kale, collards, broccoli and Asian greens have all bolted. In spring we usually have lots of cabbage, broccoli, collards and kale. Maybe we should do some earlier chard this year to make up for lack of broccoli and troubles with cabbage and over wintered kale?

Collards and kale
Young collard plant (Morris Heading, I think) Pam Dawling

In mid-March we will be transplanting Vates kale and Champion or Georgia Green collards directly from the soil in our hoophouse out into the garden. We usually grow Morris Heading collards but this year we are trying something different. We’ll use rowcover for the first few weeks. I have written before about bare-root transplants. This method saves us a lot of time, and saves greenhouse space. See Workhorse Crops in February for details about sowing these crops in the hoophouse.

Potatoes

Another mid-March task for us is potato planting. I wrote a whole series about every stage of potato growing last year. So I won’t say more here.

Hoophouse beans
Tomatoes, green beans and cucumbers in June.
Photo Alexis Yamashita

We don’t grow green bush beans in our hoophouse every year, but this year we will. As with other late winter/early spring hoophouse crops, we sow beans in our hoophouse a month earlier than we can sow outside. We aim to sow in the hoophouse on March 20. Of course, if it is particularly cold then, we will wait. We’ve found that beans sprawl more in our hoophouse, so we buy an upright fast-maturing variety, such as Strike.  We’ve also found that the edge beds are too cold for beans in late March, so if the crop rotation would have us use an edge bed, we sow beets or some other crop instead. We will use thick rowcover on nights that are forecast to be frosty outdoors. See mention of hoophouse beans in January.

Hoophouse tomatoes
March hoophouse bed prepared for tomato transplants – holes dug, compost added.
Photo Wren Vile

Mid-March is our target transplanting time for tomatoes in the hoophouse. We grow two beds, one of earlies (less than 71 days) and one bed of reliable favorites (Tropic, Jubilee) along with two plants each of other varieties we like or are trying out. Each 96ft (29 m) bed has two cherry or grape tomato varieties, with two plants of each. We plant the shortest varieties at the east end and the tallest (the cherries) at the west end, so that all the plants get the best possible light. (Our hoophouse has the long walls on the south and north.) We update our Tomato Rampancy Rating list each year.

This year in the early bed, we are growing Five Star Grape 62d, Sun Gold 57d, Garden Peach 71d, Mountain Magic 66d, Stupice 62d and Glacier 56d. Mountain Magic is a new favorite (it doesn’t suffer from green/yellow shoulders) and we have increased the number of those plants, reducing numbers of Stupice and Glacier.

Hoophouse tomatoes with yellow shoulders. Glacier or Stupice.
Photo Pam Dawling

In the other bed we are growing Cherry Bomb 64d, Black Cherry 64-75d, Geronimo78d, Striped German 78d, Amy’s Sugar Gem 75d, Green Zebra 72-86d, Cherokee Purple 72-85d, Tropic 80d, Jubilee 80d, Estiva 70d, Pink Boar 75d, and Mountain Fresh Plus 75d.

We use the Florida string-weaving (or basket-weaving) technique to support our plants. More about that task in future.

Indoor sowings for later transplanting outside or in the hoophouse

In March we will sow our hoophouse cucumbers and squash, and our outdoor peppers, eggplant, maincrop tomatoes, and our first outdoor zucchini and summer squash. And some non-workhorse crops. Also, we start our sweet potato slips. I covered growing sweet potato slips in another post. On March 24 we start our chard, as already mentioned.

Workhorse Crops to Harvest in March

Collards and Kale can be harvested outdoors here in March, from overwintered plants. This past fall, we were late getting our kale established and the combination of a mild December and a cold January has damaged them badly. We had 3 nights in January down to 10°F (-12°C). Normally we can harvest those beds once a week each in March. Our mnemonic for sustainable harvesting of leafy greens is “8 for later”, meaning we leave at least eight inner leaves when harvesting the outer ones, to ensure the plants have enough strength to regrow.

Overwintered Carrots and Cabbage are a possibility some years, but not this one!

Garlic scallions prepared for sale. Typepad.com

Garlic scallions are ready to harvest here from mid-March. These baby garlic plants offer a welcome change form leafy greens and root vegetables. We start to dig the plants once the leaves have reached 7” (18 cm). Wash and trim, cook and enjoy! Yes, you can eat them raw if you like! Some years we have made a big planting, and it has provided for us into May (when they are starting to bulb).

Hoophouse Workhorse Harvests in March

Our Red and White Russian kales are now producing well. These are Siberian-type kales, that keep growing (a bit!) in cold weather. We harvest the outer leaves and stand them on end in a bucket in a little water. The wilt very easily, so we try to keep them in the shade and get them to the cooler promptly.

White Russian kale ready for harvest in our hoophouse. Photo Pam Dawling

Bulls blood beet greens, chard, and some greens not in our Workhorse group, (turnip greens, and spinach) are still going strong. Our experimental carrots are still doing OK, although I’m not a fan of giving them hoophouse space for such a long time with no harvests. I think we would have done better to harvest them in December. The foliage is getting bedraggled, and I fear the roots are getting woody and less sweet. This is all an experiment by one of the others on the crew, who will be studying the results.

Workhorse Crops from Storage in March

In March we can eat carrots, garlic, potatoes, sweet potatoes, winter squash and cabbage from storage, while they last. We do still have potatoes, sweet potatoes and butternut squash. Also we have frozen summer goodies, and pickled things, sauerkraut, pickled beans, and canned goods like salsa.

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

Workhorse Crops Special Topics for March: DIY Weather Forecasting

Learn your local weather patterns by keeping records of daily max and min temperatures and rainfall, and watching what happens.

Our mid-Atlantic climate is controlled by three weather systems, mainly by moisture from the Gulf of Mexico, the Bermuda High Pressure area in summer, and recurrent waves of cold Canadian air in winter.

Rain (statistically fairly evenly distributed throughout the year in our county) has slight peaks in January, February and March and again in early June and August.

Some parts of our area can experience long periods of drought: September-November is the drier season but it’s also the hurricane season, so the net result is very variable.

We use Wunderground forecasts, but subtract 5F° (2.5C°) from their forecast night lows for our nearest town, and mentally downgrade the chance of rain by 10%, as rain often passes us by as it scoots along the river valley north of us. 3/30 pm in winter is a good time to look at the night forecast.

WeatherSpark is a great resource. You can enter your zipcode or town and discover a large range of charts and graphs about weather in your area. It will help you learn what to expect.

Immature frosty cabbage. Photo Lori Katz

As for predicting frost, here are some of the factors to consider, that make frost more likely here:

  • If the date is after 10/14 or before 4/30 (ie within the average range for frosts here)
  • If the Wunderground forecast low for Louisa Northside is 37°F (3°C) or less.
  • If the daytime high temperature was less than 70°F (21°C).
  • If the temperature at sunset is less than 50°F (10°C).
  • If the sky is clear.
  • If the soil is dry and cool.
  • If the moon is full or new.
  • If there is little or no breeze, although if temperatures are falling fast, the wind is from NW and the sky is clear, then polar air may be moving in, and we’ll get a hard freeze.
  • If the dew point forecast is low, close to freezing, a frost is more likely. Frost is unlikely if the dew point is 43°F (6°C) or more.

Getting ready for frost and colder weather

 

Eat-All Greens rows with frost in December. October and part of November are still productive growing weeks in central Virginia. Photo Bridget Aleshire

Gardening does not end with the first frost! We will work our way from clearing the least hardy crops to those we can leave outside all winter. See our table Winter Kill Temperatures of Cold-Hardy Vegetables. We will harvest or cover all the frost-tender crops, make a last harvest of rhubarb (the stems are hardy to 22°F (-6°C)) and hoop and rowcover the last outdoor lettuce. Our June-planted potatoes will be our last big harvest for the year.

We pull up the biggest Purple Top turnips and Cylindra beets, leaving the others a bit more room to size up before their killing temperature of 12°F (-11°C). Any day now, we’ll start harvesting fall leeks (King Richard and Lincoln), keeping the winter-hardy ones (Tadorna) for the winter.

DIY weather-forecasting

I recommend learning your local weather patterns by keeping records and watching what happens. Here’s what I’ve learned about ours:

Our mid-Atlantic climate is controlled by three weather systems,

  • mainly by moisture from the Gulf of Mexico,
  • the Bermuda High Pressure area in summer,
  • and recurrent waves of cold Canadian air in winter.
Beds after rain, Photo Wren Vile

Rain (statistically fairly evenly distributed throughout the year in our county) has slight peaks in January, February and March, and again in early June and August.

Some parts of our area can experience long periods of drought. September-November is the drier season but it’s also the hurricane season, so the net result is very variable.

We use Wunderground.com  but subtract 5F° from their forecast night lows for our nearest town, and mentally downgrade the chance of rain by 10%, as rain often passes us by as it scoots along the river valley north of us.

Blackberry leaf with frost.
Photo by Ezra Freeman

Our average first frost date is October 14. Actually from our own records it has averaged 10/20 (13 years of our own records). So it’s time to start thinking about frost. It’s good to be prepared.

According to Dave’s Garden in Louisa County where I live, the threshold of 36°F (2°C) has a 50% likelihood on Oct 3; the 32°F (0°C) threshold has a 50% likelihood by Oct 13 and the 28°F (-2°C) threshold is as likely as unlikely by Oct 27. The 90% chances occur by Oct 14, Oct 28 and Nov 12 respectively.

Another great website for local weather info is WeatherSpark.

Now that climate change is here, it pays to be ready for weather different from what we have experienced previously. Keeping records helps, as does having good thermometers for air and soil.

Four Ranges of Cold-Hardy Crops for Harvest at Various Stages of Winter

This simple model helps reduce confusion and set priorities

1. Crops to harvest before cold fall weather (32°-25°F) and store indoors:

Michihili Chinese Cabbage. Photo Southern Exposure Seed Exchange

Chicory for chicons or heads; crosnes/Chinese artichokes, dry beans,  Chinese cabbage, peanuts, “White” Peruvian potatoes at 32°F (0°C) approximately, pumpkins, seed crops, sweet potatoes at 50°F (10°C), winter squash.

2. Crops to keep alive in the ground into winter to 22°-15°F (-6°C to -9°C), then harvest.

Bucket of freshly harvested Detroit Dark Red beets for storage.
Photo Pam Dawling

Store: Beets before 15-20°F (-9.5 to -7°C), cabbage, carrots before 12° F (-11°C), celeriac before 20°F (-7°C), kohlrabi before 15°F (-9.5°C), winter radish including daikon before 20°F (-7°C), rutabagas, turnips before 20°F (-7°C).

Use soon: Asian greens, broccoli, cabbage, chard, lettuce, radishes

3. Hardy crops to store in the ground and harvest during the winter.

Using a sturdy digging fork to harvest leeks in December.
Photo Pam Dawling

In zone 7, such crops need to be hardy to 0°-10°F (-17.8°C to -12.3°C): Collards, horseradish, Jerusalem artichokes, kale, leeks, parsnips, scallions, spinach.

4. Overwinter crops for spring harvests before the main season.

A stormy winter day, garlic, rowcovered spinach beds and our hoophouse.
Photo Wren Vile

In zone 7, they need to be hardy to 0°-10°F (-17.8°C to -12.3°C): Cabbage, carrots, chard, collards, garlic and garlic scallions, kale, multiplier onions (potato onions), scallions, spinach.

Frost is more likely at Twin Oaks if:

  • The date is after 10/14 (or before 4/30).
  • The daytime high temperature was less than 70°F (21°C).
  • The sky is clear.
  • The temperature at sunset is less than 50°F (10°C).
  • The dew point forecast is low, close to freezing. Frost is unlikely if the dew point is 43°F or more.
  • The Wunderground 3.30pm forecast low for Louisa Northside is 37°F (3°C) or less.
  • The soil is dry and cool.
  • The moon is full or new.
  • There is little or no breeze, although if temperatures are falling fast, the wind is from NW and the sky is clear, then polar air may be moving in, and we’ll get a hard freeze.
Ice on the pond.
Credit Ezra Freeman

Frost Alert Card

For just this time of year, we keep a Frost Alert Card reminding us which crops to pay attention to if a frost threatens. We check the forecast online at 3.30 pm (we find that’s late enough to be fairly accurate about night temperatures and early enough to give us time to get vulnerable crops covered).

The big decision is the triage of harvest/cover/let go. Our list is not just crops that will die with the first frost but also ones that will soon need covering as temperatures decrease.

  • Cover lettuce, zucchini, summer squash, cucumbers, beans, Chinese cabbage, pak choy, lettuce and celery.
  • Harvest crops listed above that can’t or won’t be covered.
  • Harvest all ripe tomatoes, eggplant, corn, limas, cowpeas, okra, melons.
  • Harvest peppers facing the open sky, regardless of color. (Often only the top of the plant will get frosted).
  • Check winter squash and harvest any very exposed squash.
  • Set up sprinklers for the night, on tomatoes, peppers and a cluster of beds with high value crops.
Peppers that are protected by leaves can survive a light frost. Photo Pam Dawling

We really like this pepper strategy we have developed: by picking just the peppers exposed to the sky, we reduce the immediate workload (and the immediate pile up of peppers in the cooler!) and we often get a couple of milder weeks after the first frost before the next. By then the top layer of leaves that got frosted the first time will have died and a whole new layer of peppers will be exposed and need harvesting. This way we get fewer peppers at once, and a higher percentage of ripe peppers, which have so much more flavor.

Our overhead sprinkler strategy is useful if a frost is coming early when we still have many tomatoes we’d like to vine-ripen. Keep the sprinkler running until the sun is shining on the plant sin the morning, or the sir temperature is above freezing again. The constant supply of water during the night does two things. First water gives off heat as it freezes. Yes, really. It’s easier to understand ice taking in heat to melt, but the flip side is that water gives off heat as it freezes. This latent heat of freezing helps warm the crops. And if ice does form, the shell of ice around the plants stops more cold damage happening.

Frost Alert List

Task

Crop

Notes

 

Harvest all edible

Asparagus beans

 

Harvest all edible

Eggplant

 

Harvest all edible

Okra

 

Harvest all edible

Tomatoes

Including green ones

Harvest all edible

Peppers exposed to the sky

 

Harvest all edible

West Indian gherkins

 

Harvest all edible

Pickling cucumbers

 

Harvest all edible

Corn

 

Harvest all edible

Beans #4, 5, 6, then cover

Uncover once mild again

 

 

 

Thick row cover

Squash

Spring hoops or none. Ditto

Thick row cover

Slicing cucumbers

Spring hoops or none. Ditto

Thick row cover

Celery

Double hoops – leave covered

Thick row cover

Last lettuce bed

Double hoops – leave covered

Set sprinklers

Slicer tomatoes

Overnight from before 32F till after sun shines on plants

Set sprinklers

Roma paste tomatoes and peppers

Ditto

Set sprinklers

Other vulnerable raised bed crops

Ditto

Sun Gold cherry tomatoes. Pick the green and the ripe ones before a frost.
Photo Pan Dawling

Cold Weather Crop Protection

  1. Rowcover – thick 1.25 oz rowcover gives about 6F (3.3C) degrees of frost protection. Use hoops.
  2. Low tunnels and Quick Hoops are wider version of using rowcover. They need the edges weighting down. Best for climates where the crops are being stored in the ground until spring, when they start growing again. Less useful in climates like ours which have very variable winter temperatures, and are warm enough that we realistically expect to harvest during the winter, not just before and after.
  3. Caterpillar tunnels – 2 beds plus 1 path, tall enough to walk in. Rope holds cover in place, no sandbags.
  4. High tunnels (= hoophouses), single or double layer. Double layer gives 8F (4.5C) degrees of protection, plus plants can survive 14F/8C colder than they can outside, without extra rowcover; at least 21F/12C colder than outside with thick rowcover. Leafy crops are not weather-beaten. We strongly believe in two layers of plastic and no inner tunnels (rowcovers) unless the night will be 8°F (-13°C) or colder outdoors.

Hoophouse Notes

Salad greens in a hoophouse in zone 7 can survive nights with outdoor lows of 14°F (-10°C). A test year: Lettuce, Mizuna, Turnips, Russian kales, Senposai, Tyee spinach, Tatsoi, Yukina Savoy survived a hoophouse temperature of 10.4°F (-12°C) without rowcover, -2.2°F (-19°C) with. Brite Lights chard got frozen leaf stems.

Rolls of rowcover in our hoophouse ready to pull over the beds on very cold nights.
Photo Wren Vile

Other Posts on These Topics

10/18/16 Getting Ready for Frost

10/21/19 Preparing for Frost and Cold Weather

10/19/20 Harvest and Maturity Indicators in Vegetable Harvests.

10/16/18 Season Extension and Frost Preparations

Getting ready for frost, harvesting sweet potatoes

Sweet potato harvest. Photo Nina Gentle
Sweet potato harvest.
Photo Nina Gentle

Our average first frost date is October 14. Actually from our own records it has averaged 10/22 over the last 11 years. So any time now, we could get a frost. We had a very light patchy frost 10/10 with a recorded overnight low of 36F, but now we are having a warm spell (very nice). It’s good to be prepared. We harvested our sweet potatoes (not a good yield, too many deer). We are getting ready to harvest our white potatoes.

DIY weather-forecasting

I recommend learning the local weather patterns by keeping records and watching what happens. Here’s what I’ve learned about ours:

  • Our mid-Atlantic climate is controlled by three weather systems,
    • mainly by moisture from the Gulf of Mexico,
    • the Bermuda High Pressure area in summer,
    • recurrent waves of cold Canadian air in winter.
  • Rain (fairly evenly distributed throughout the year in our county)
    • has slight peaks in January, February and March
    • and again in early June and August.
  • Some parts of our area can experience long periods of drought.
    • September-November is the drier season but it’s also the hurricane season, so the net result is very variable.
  • We use Wunderground.com but subtract 5F° from their forecast night lows for our nearest town, and mentally downgrade the chance of rain by 10%, as rain often passes us by as it scoots along the river valley north of us.

Local Information

According to  a Freeze / Frost Occurrence Data pdf for Virginia which I have, in Louisa County the threshold of 36F has a 50% likelihood on Oct 3; the 32 F threshold has a 50% likelihood by Oct 13 and the 28F threshold is as likely as unlikely by Oct 27. The 90% chances occur by Oct 14, Oct 28 and Nov 13 respectively. The data for spring are available here. probably the site has the fall info too, but I’m out of time to look, due to three hours without internet this afternoon.

Frosty daikon leaves. Photo Bridget Aleshire
Frosty daikon leaves.
Photo Bridget Aleshire

Help predicting frost

We keep this reminder list handy at this time of year, when trying to make our own frost forecasts:

Frost is more likely at Twin Oaks if:

  • The date is after 10/14 or before 4/30.
  • The daytime high temperature was less than 70°F (21°C).
  • The sky is clear.
  • The temperature at sunset is less than 50°F (10°C).
  • The dew point forecast is low, close to freezing. Frost is unlikely if the dew point is 43°F or more.
  • The Wunderground 3.30pm forecast low for Louisa Northside is 37°F (3°C) or less.
  • The soil is dry and cool.
  • The moon is full or new.
  • There is little or no breeze, although if temperatures are falling fast, the wind is from NW and the sky is clear, then polar air may be moving in, and we’ll get a hard freeze.

We also make for ourselves a Frost Alert Card, so we can quickly know which beds we need to attend to if we decide a frost is likely. (RBs means raised beds)

Task Crop Notes
Harvest all edible Asparagus beans
Harvest all edible Eggplant
Harvest all edible Okra
Harvest all edible Tomatoes Incl green
Harvest all edible Peppers exposed to the sky
Harvest all edible West Indian gherkins
Harvest all edible Pickling cucumbers
Harvest all edible Corn
Harvest all edible Beans #4, 5 Uncover once mild again
Thick row cover Beans #5,6 Ditto
Thick row cover Squash Spring hoops or none. Ditto
Thick row cover Slicing Cucumbers Spring hoops or none. Ditto
Thick row cover Celery
Thick row cover Last Lettuce bed Double hoops – leave covered
Set sprinklers Slicer tomatoes Overnight from before 32F till after sun shines on plants
Set sprinklers Romas and peppers Ditto
Set sprinklers Other vulnerable RBs Ditto

FrostProtectionFundamentalsPracticeandEconomicsFAO.pdf

is a 126 page book which includes explanations of freezes and frosts (both radiation frosts and advection frosts), and a chapter on recommended methods of frost protection for food crops. probably none of us will need the information on wind machines and helicopters (maybe little drones work for small scale growers?). The publication includes frost forecasting and frost damage physiology (for growers not in a panic about immediate frosts, who want to understand what the plants are going through).

Potato harvest November 2015 Photo Lori Katz
Potato harvest November 2015
Photo Lori Katz