Get A Jump-Start on Cool-Season Crops

The tail-end of winter is the perfect time to plant seeds of your favorite cold-hardy crops in preparation for the upcoming spring.

by Jessica Walliser
PHOTO: Karolina/Pexels

With March’s arrival, it’s time to start thinking about getting a few cool-season vegetables started. If you enjoy growing your own veggie transplants from seed and you live in a climate with cold winters, now’s the time to start sowing the seeds of cool-weather crops indoors under grow-lights—if you haven’t done it already.

Cool-Season Crops To Start With

The list of cool-season crops that can be started from seed right now is extensive and includes varieties like:

  • kale
  • kohlrabi
  • lettuce
  • cabbage
  • broccoli
  • Brussels sprouts
  • cauliflower
  • pac choi
  • collards
  • celery
  • mustard greens
  • cilantro
  • mizuna
  • arugula
  • chard

Because these crops are highly tolerant of cold weather and the flavor of many of them is actually sweetened by exposure to frosts, transplants can be planted out into the garden very early in the season. In order to have sizeable plants when outdoor planting time arrives in three to six weeks, you should start your seeds right now.

Starting Your Seeds

To do that, sow seeds of these cool-season crops anytime from mid-February to mid-March. For the best results, use a seedling heat mat to warm the soil beneath the germinating seeds, but remove it as soon as most of the seeds have sprouted. This keeps the plants from getting too leggy.

You’ll also want to use a grow light to encourage short, stocky, healthy seedling growth. Grow lights should be positioned 2 to 3 inches above the plant tops and raised as the plants grow. Lights should remain on for 18 to 24 hours per day for optimum growth. If you don’t have grow lights, a 4-foot-long, florescent tube shop-light will provide enough light for good seedling growth.

Transplanting Your Seeds

Once the seedlings produce their first set of true leaves, they should be separated and transplanted into slightly larger containers. This is also the time when fertilization should begin. Use an organic, liquid fertilizer, diluted to half the recommended strength, to fertilize the seedlings once every week.

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As soon as the seedlings are 3 to 4 inches high and the daytime temperatures are regularly in the 50s or above, it’s time to transplant your seedlings out into the garden. Before moving them outdoors permanently, however, they’ll need to be slowly acclimated to outdoor growing conditions—a process known as hardening-off.

To harden-off seedlings, move the flats outdoors and place them in a shady location for two hours per day. Over the course of two weeks, gradually increase the amount of time the seedlings spend outdoors and the amount of sunlight they receive. At the end of the two-week period, the seedlings should be located in an exposed area, in full sun, and outdoors all day and night.

After this hardening-off period, it’s time to transplant your cool-season crops out into the garden. If you’d like, you can offer them a little extra protection by covering the newly planted transplants with a cloche made from a bottomless milk jug with the cap removed. Cloches help protect plants from weather extremes and give them a jump-start on the growing season by keeping them cozy, but they aren’t necessary. Cool-season crops, such as those listed above, are frost tolerant and ready to handle whatever Mother Nature dishes out.

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