Growing A Better Garden: Cool season crops

Published 9:26 am Thursday, February 23, 2017

By Pam Jones

Cooperative Extension

Horticulture Agent

Cool season crops are plants that grow best during cool temperatures and short days.

Cool season vegetables originated in more temperate climates than warm season vegetables, which originated in subtropical and tropical climates. Cool season crops tolerate some frost and can be planted in the early spring and late summer going into fall.

When planted in the fall, most should be planted early enough to mature before hard freezes are predicted.

Cool season vegetables can be planted before the soil temperatures are high enough to plant warm season vegetables. Soil temperature is just as important as the daily highs and lows of the air temperature and must be taken into account.

The NC CRONOS Database, developed by the State Climate Office of North Carolina, enables the public to quickly and easily retrieve observations from 12,983 active weather sites in and around North Carolina. The closest weather database for this information is the Piedmont Research Station in Salisbury.

Data includes soil temperature and moisture as well as high and low air temperatures, rainfall, and other data valuable to farmers and gardeners.

The table below reflects the mean, high and low soil temperatures recorded in Salisbury on Sunday Jan. 19 at a four-inch soil depth: Mean temp(max+min)/2, 52.2°F; High temp, 59.3°F; Low temp, 45.1°F.

Gardeners can also measure their own soil temperature by buying a soil thermometer. Soil thermometers are relatively inexpensive and are available at garden centers and online. Measure the soil at a depth of 4 inches.

Most cool season vegetables can be planted when the soil temperature is 50 degrees or above. These include: leaf lettuces, onions, garlic, shallots, parsnips, mustard greens, turnips, beets, peas, carrots, kohlrabi, cauliflower, broccoli, radish, cabbage, spinach, peas, Kale, collards and Swiss chard.

Seeds planted too early, before soil temperatures are warm enough, sit in the soil and don’t germinate until soil temperatures are warm enough for germination. Seeds may rot before germination if there is enough soil moisture.

This year, weather and horticultural analysts are reporting that higher temperatures are causing plants to be two weeks ahead of schedule. While this may be early to plant some cool season vegetables, remember that cool season plants can tolerate some frost.

Row covers designed for cold protection are also available for extremely cold temperatures. Most give a 3-4°F increase in temperature when unexpected hard freezes are predicted.

For a comprehensive calendar on planting times for specific plants, consult the Central NC Planting Calendar for Annual Vegetables, Fruits, and Herbs. It can be found online at or you can pick up a copy at the Davie Extension Center, 180 S. Main St., Mocksville, in the red brick building beside the courthouse.

Plant some cool season vegetables and let me know how your garden grows.

Next in the series will be challenges facing gardeners such as insects, diseases, weather and weeds.