Cool season vegetables are the ones that you can put in your garden beds before the last frost. Early spring planting is ideal. They can handle a light or moderate frost, survive, and prosper. Some of them even prefer a few frosts to develop flavor and provide the maximum yield. Most of them don't like the high temperatures of summer.
Cool season plants that should thrive in cool conditions include: broccoli, Brussels sprouts, cabbage, cauliflower, celery, kale, kohlrabi, lettuce, mustard greens, onions, peas, potatoes, radish, rutabaga, spinach, turnip. Beets, carrots, chard, and parsnips are cool season vegetables that can also handle warmer temperatures of summer.
Most of these cool season vegetables do best when planted two to four weeks before the last frost. Individual seed packets will offer guidance for specific planting time. With a little preparation, you can get them in the ground and growing long before the rest of your garden.
Sow the seeds directly into the soil. Check your soil temperature before planting (see my blog on that subject). As long as the soil is above 40 degrees F, the seeds should germinate if kept moist in an amended soil. A few of the plants like cabbage, chard, potatoes, and turnips will do better if the soil is at least 50 degrees F. For best results some of these vegetables do better as young plants rather than seeds; transplant broccoli, cabbage, cauliflower, and onions if you have the option.
The air temperature shouldn't be more than a few degrees below freezing on the coldest nights and should be consistently above 40 degrees F during the day. You can do a few things to help protect the plants while night temperatures remain low. Mulching the young plants with straw or grass can help insulate them and moderate soil temperatures. Row covers will help protect plants from a light frost. If a hard freeze below 28 degrees F is forecast, cover the plants with a sheet or blanket overnight; plastic will work, but can freeze any leaves or plants that it touches.
There are perennial vegetables that also fall into the cool season category. Asparagus, horseradish, and rhubarb are great additions to a garden and will return year after year. All three can be planted as soon as the ground can be worked in spring; when it's no longer frozen. They will be among the first of your plants to break ground in future years. Choose their home carefully because they'll become permanent fixtures in your garden once established.
If you have limited room in your garden, cool season vegetables can provide multiple harvests in the same plot. An early planting of lettuce or spinach will provide ample produce for your kitchen. Just about the time they begin to suffer from higher soil and air temperatures, you can remove them and plant tomatoes or squash in the same space. The combination of cool season vegetables early in the season and warm season vegetables later in the season is endless.
Here's another secret to keep in your back pocket. Many of these cool season vegetables will grow well in the fall too. A late summer planting will provide a harvest after the first frost of fall. You may get three different crops in the same garden plot. Look forward to more information about that when I discuss it during the summer.
For now, enjoy an edible garden with frost on the ground. By the time you start thinking about planting tomatoes, squash, and corn, you'll already have harvested radishes, lettuce, peas and more wonderful, cool season vegetables. It's not too early to begin.