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 our hardy vegetables. Tender vegetables are typically planted on the average frost-free date where there is still a 50/50 chance there will be 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 actually 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 will 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 originated, 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, yet 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 just 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 “time to plant.”
Learn more at go.illinois.edu/WhenToPlant.
About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.