When gardeners talk about tender or warm-loving vegetables, the conversation is not about how caring and affectionate the vegetables are, but how they need warmer air and soil temperatures to get off to a good start.
Track temperatures for tender vegetables
Tender vegetables are those that cannot survive even a light frost and that like a warmer soil temperature than hardy vegetables. Tender vegetables typically are planted on the average frost-free date where there still is a 50/50 chance of a frost. This means that if a frost is predicted, gardeners should have their old blankets, sheets and lightweight traps handy to cover those vegetables for the night. Every day after that frost-free date, there is less of a chance of having a frost.
The list of tender vegetables is considerably shorter than that of the very hardy and hardy vegetables. Tender vegetables, usually sown from seed, include snap beans, sweet corn, New Zealand spinach and summer squash. Those vegetables sown from seed are not likely to be damaged by an above-ground frost yet need the warmer soil to start to germinate. By the time those seedlings emerge, the likelihood of a frost is really reduced. The most common tender vegetable is not planted by seed but rather by transplant – the tomato. It will be tomatoes that you will have to watch out for. Even without the chance of frost, gardeners often provide some cold weather protection using temporary covers to encourage growth as the air temperatures continue to be on the cool side during the day.
Wait for warm-loving vegetables
Warm-loving vegetables really need both the soil and air temperatures to be warmer than all the rest and should not be put in the garden until two weeks after that magical average frost-free date. Many of our popular garden plants are in this group, including pepper, eggplant, cucumber, lima bean, okra, winter squash, watermelon, pumpkin, sweet potato and muskmelon.
If you think about where most of our vine crops originate, it makes sense that they really need the warm soils to get started and the warmer air temperatures to flourish. It also is more clear why summer squash is planted before the winter squash; you want the winter squash to mature as late in the season as possible so it will store longer into the winter months, and we want to eat the softer-skinned summer squash during the growing season. Transplants for our warm-loving vegetables typically are the peppers and eggplants, and some of the vine crops also been showing up at the retail garden centers.
Practice patience for a better season
It is so easy to get caught up with “garden fever” early, but patience is the key to planting your vegetables at the right time to get the best yields throughout the season. The soil temperature on bare ground a week ago at a depth of 2 inches was 40 degrees Fahrenheit. Dark soils warm quicker than lighter soils, as would raised beds and planter bags. In the end, you know your yard better than anyone else when it comes to the time to plant.
Learn more at go.illinois.edu/WhenToPlant. Have questions for the University of Illinois Extension Master Gardeners? Learn more about connecting with a local Master Gardener Help Desk at go.illinois.edu/HelpDeskMGdkk, or call or visit during office hours: 9 a.m. to 12:30 p.m. Monday, Wednesday, and Friday, at 630-553-5823 or 7775-B Route 47, Yorkville.
• Richard Hentschel is a Horticulture Extension educator with University of Illinois Extension, serving DuPage, Kane and Kendall counties. This column originates on his blog at go.illinois.edu/overthegardenfence. To get more tips from Hentschel, watch his “This Week in the Garden” videos on Facebook and YouTube.