Sometimes I teach vegetable gardening, as it was my original gardening passion and the topic of my first book writing for Rodale. I have learned to clarify some basic premises to make vegetable gardening easier for new gardeners or the experienced-but-confused. One of the most helpful things to understand is which plants are worth starting from seed, and which ones do best if you plant them as seedlings or larger plants.
Today I am writing about planting seeds in the ground — not seed-starting at home. While some dedicated gardeners do start plants under lights or in greenhouses, it is frankly not so easy to do — more on that later. On the contrary, planting seeds in the garden is easy, satisfying, and feels so right. It’s what people have done since the beginning of — gardens! Let’s figure out which crops to seed, and how, and when.
Cool-season crops to grow from seed
The "cool season" is often a missed opportunity in Western New York, but some crops grow much better in cold soil. When days get warm these plants bolt and become bitter or go to seed. Consider the cool season the weeks between the soil thawing (perhaps in April) and the soil warming up to about 55 degrees (typically in late May or early June). If the soil feels cold to your hand, it’s still the cool season.
Leafy greens: Lettuces, kale, Swiss chard, spinach, and mesclun (mixed salad greens) can be planted successfully as soon as the top inch of soil is workable. Typical package instructions say: "Plant two to four weeks before the last frost date" (around May 20 in much of WNY). They germinate best when the soil is well below 65 degrees, and not warmer than 70 degrees. Sometimes it works to plant lettuce seeds in the fall; they get started, stall in place during winter, and start up again in spring. These plants also grow well in cold frames or hoop houses, even through the winter in many situations. Once a heat wave arrives, leafy greens all bolt. You can slow down the process by covering them with a shade cloth or window screen when warm days are coming.
Peas (bush or climbing): Old-timers mention planting peas at Easter time, and some even mention St. Patrick’s Day. A more dependable gauge: If you can stick your finger one inch into the soil, you can put a pea in there. They germinate in soil warmer than 40 degrees, and the seeds will die in soil past 70 degrees.
Root crops: Beets, carrots, parsnips and radishes are quite cold-tolerant. Plant radishes soonest: four to six weeks before the last frost (typically in early April). Plant other root crops two to four weeks before the last frost date. If you can acquire a soil thermometer, it is the best tool for guiding these judgments: Root crops grow best when the soil is 60 to 75 degrees and the air warmer than 50 degrees.
The cabbage or Brassica family, also called "cole crops," are considered cool-season vegetables as well. Many even survive deep freezes. You may have luck growing them from seed, but it takes them a long time to grow and then they bolt in the June heat, so it is much easier to plant them as seedlings. They are readily available in farmers markets or garden centers, where they have been started by professionals who were able to provide the perfect cold start-up conditions. Plant them when you can acquire them in the market. If you have a choice, plant four or five weeks before the last frost (and cauliflower just two weeks before that date—perhaps early May). Cauliflower does not survive a deep freeze.
Warm-season crops to grow from seed
Beans (both bush and climbing): Plant when the soil is warm, ideally 70 degrees.
Vine crops (squash, pumpkins, cucumbers): Require warm soil (70 degrees) and nights warmer than 60 degrees. You can buy the little plants, but they are very easy to grow from seed.
The nightshade family includes tomatoes, eggplants, peppers, and potatoes: Except for potatoes, these plants don’t grow very well from seed in our climate — it just takes too long. They are warm-season crops: not just heat-loving but heat-requiring. Not only are the plants killed by frost, they are also damaged by soil cooler than 60 degrees and nights cooler than 55 degrees. (They typically develop birth defects such as cracking and cat-facing.) So buy sturdy plants from a grower, and plant them after Memorial Day. (Several studies show that June-planted tomatoes catch up with their taller brothers that were planted — at risk — in mid-May.) In spite of giving this advice in many media for 25 years, I know I’ll hear the question in April in a garden center: "Where are the tomato plants?"
Potatoes are tricky, and sort of an in-between the cool and warm season timing. Plant "seed potatoes," cut with a few "eyes" on each piece, about three weeks before the frost date. In a cold, wet spring they may rot in the ground however; they grow best when soil is 50 degrees.
Why seed and not lights?
I mentioned that growing under lights is not easy, although it can be a great experience. If you have an attached sun room or greenhouse, or can prepare a good light setup, go for it. (Study the timing carefully.) Windowsill light is rarely enough. If you’re counting on a good crop of vegetables, don’t trust that your first crop under lights will be highly productive. Many plants don’t get enough light or the right temperatures, and they become leggy and yellowish before it’s safe to put them outside. If you’re succeeding at growing under lights—good for you!
For the rest of us, just straighten out the warm crops from the cool crops. Then plant those seeds in the soil.
Sally Cunningham is a garden writer, lecturer and consultant.