"Some like it hot, some like cold." This familiar refrain from the old nursery rhyme is as true for vegetable seedlings as it is for pease porridge. Veggies can be divided roughly into those that relish the cool growing conditions of spring and fall, and those that demand warm air and soil in order to sprout and flourish. Knowing which category a particular vegetable falls into is helpful in deciding when to sow seeds, either early indoors under lights or directly out in the garden, as well as when to set out transplants.
Some Like It Cold
Well, maybe not cold, but certainly cool. The list of cool-season crops includes many kinds of greens, root crops, and members of the cabbage family. Spinach is one of the hardiest of the greens, and seeds can go directly in the garden as soon as the soil is dry enough to work in the spring. But there are many other tasty, hardy greens that will give you an early season harvest, including arugula and many Asian greens such as mizuna, taht soi, and pak choi.
Peas of all sorts ? English or sugar (snow) ? are other classic cool-season crops that grow best from seeds planted as soon as the soil is ready in the spring. (You can even make your own pease porridge from your harvest! This traditional British dish is made from dried split peas, cooked up to a pudding-like consistency. For drying, choose a smooth seeded, high starch pea variety like Alaska.) Radishes, beets, carrots, and turnips will taste sweetest if they mature when temperatures are on the cool side, so they are good candidates for sowing both in early spring for a harvest before the heat of summer hits and again in late summer for a fall harvest.
Some cool season crops will benefit from an early start indoors. Hardened off transplants of cabbage and kale can go out in the garden as early as 4 weeks before the last frost date; wait until 2 weeks before the last frost date to set out broccoli and cauliflower seedlings. Start seeds of these crops 4-6 weeks before you plan to transplant to the garden.
Some Like It Hot
Then there are the vegetables that want nothing to do with cool spring weather. These are the heat lovers that need warmth for seed germination and good growth. Frost will finish them off, so outdoor seed sowing and transplanting must wait until the soil is nice and warm, the weather is settled, and all danger of frost is past. Tomatoes and their relatives, eggplant and peppers, fall into this category, along with beans, corn, okra, and members of the cucurbit family ? melons, squash, pumpkins, and cucumbers. Gardeners aiming for the earliest ripe tomato may push the envelope by setting out their transplants with some type of protection when conditions are still cool, even though this can be a bit of a gamble.
As with cool-season crops, some warm season crops do best if they are started early indoors and transplanted. These include tomatoes, peppers, and eggplant. However, corn and beans will do best if seeds are sown where they are to grow. Cucumbers, melons, squash, pumpkins, and okra can be started early indoors. But they resent the root disturbance that comes with transplanting, so if you're starting these crops early sow seeds in plantable, biodegradable pots (such as peat pots). Unless you are gardening in a short-season climate, you may be better off direct sowing these touchy transplanters once conditions are warm, as direct sown plants will usually grow vigorously enough to catch up with and even overtake transplanted ones.
Tips for Cool Season Crops
Let the Soil Dry Out Don't be too eager to get out digging in the garden on the first warm days of spring. Tilling or digging in the garden when the soil is too wet will destroy its structure and leave you with a compacted mess. To test if soil is dry enough, squeeze a handful. If it sticks together in a tight ball, let the soil dry out some more before working. If the ball of soil breaks apart easily when given a gentle poke, it's ready for digging.
Prepare Ahead for the Earliest Crops The hardiest crops, such as spinach and arugula, will germinate and grow when the soil is still cool. But often the soil is still too wet in early spring to prepare the planting bed. Do your bed prep the fall before. Then you can simply poke your seeds into the soil without digging in it. If you must step into the bed to plant, lay a wide board down to distribute your weight and lessen the likelihood of compacting the soil.
Pre-sprout Peas Peas grow best when the weather is cool, but sometimes the seeds rot before they can sprout when the soil is still cold and wet. Try pre-germinating your peas to get them off to a reliable start. Wrap the seeds in a moist paper towel and put them in a dark, warm place for a few days. Check daily and as soon as you see the tiny root begin to emerge, pop the seeds into their outdoor planting bed.
Tips for Warm Season Crops
Don't Sow Seeds Too Early Stick to the recommended indoor seed starting times for your crops so that they'll be at a good size for transplanting when the weather in your area is suitable. Start tomato seeds 6-8 weeks before their setting out date, which is a week or two after your last frost date. Start slower growing peppers and eggplant 8-10 weeks before they're set outside, 2 weeks after the last frost date. Cucumbers, squash, and melons will be ready for outdoor planting in just 3 to 4 weeks. Although it may seem counter-intuitive, the further your indoor growing conditions are from ideal, the shorter the amount of time your seedlings should spend inside. The conditions of light and temperature on windowsills or even under lights are usually not good enough to support long-term growth. So get your seedlings off to a good start, but don't keep them inside so long that the limitations of indoor growing conditions begin to set them back.
Warm Up the Soil If you garden in a short-season climate, warm up soil in your garden beds before transplanting time. Spread clear, black, or infra-red transmitting (IRT) plastic over the bed two weeks prior to the planting date. (Clear plastic will give the greatest soil warming, but will also allow weeds to sprout. Black and IRT plastic will result in a little less warming but will block weed germination.) During the growing season an organic mulch such as straw is a great way to keep down weeds and conserve soil moisture in the vegetable garden. But it also keeps soil cooler, so hold off spreadin g it until the soil has warmed up, a week or so after your last frost date.
Harden Off Transplants Be sure to harden off your homegrown seedlings before setting them out in the garden. Gradually expose them to the cooler temperatures and higher light intensity of the open garden by setting them out in a more and more exposed location for increasing periods of time over the course of a week or two before planting.
Q: I've never had much luck with my spring planted cauliflower. Sometimes the heads are very small; other times leaves grow up through the heads or the heads are loose with lots of gaps. What am I doing wrong?
A: Spring-planted cauliflower can be a tricky crop to grow well because it often gets stressed by weather conditions in many parts of the country. This cabbage family member does best if the heads mature when the weather is cool, but not too cold; temperatures in the 60's are ideal. If seedlings are set out too early in the spring exposure to cold can cause the plants to "button" or form tiny heads, so wait until a week or two before the last frost date to set out transplants. However, when seedlings are set out then, this means that in many areas the heads will be maturing when the weather is too warm, leading to bitter taste and those leaves within the head you noticed. For gardeners in many parts of the country, fall planted cauliflower is often the most successful. Sow seeds for transplants in mid to late summer; then set out young plants when they are 4-6 weeks old. Spread a thick organic mulch around them to help keep the soil cool and make sure plants get consistent moisture throughout the growing season.