Published on 04/18/00

Soil Temperatures: Don't Rush Mother Nature

Your calendar and a soil thermometer will help you know the proper planting time for your garden vegetables.

Many of the vegetables we plant are from the tropics. They don't like cold soils and won't grow well in them. To get the best growth, then, plant all transplants and seeds within a certain soil-temperature range.

Spring Patience:
Minimum Soil Temperatures for Planting *
Tomatoes, cucumbers, snap beans 60º F
Sweet corn, lima beans, mustard greens 65º F
Peppers, watermelons, squash, southern peas 70º F
Okra, cantaloupe, sweet potatoes 75º F
* Take readings on three straight mornings at 1 to 2 inches for seeds and 4 to 6 inches for transplants.

Planting too early, before the soil has had time to warm up, can lead to seed rot, slow germination, poor growth and disease.

For example, cucumber seeds usually take less than a week to germinate in a soil of 70 degrees Fahrenheit. They could take two weeks in 60-degree soil. Tomato transplants need a soil above 60 degrees to grow. And setting out pepper plants before the soil is 70 degrees could stunt their growth for the entire growing season.

You can buy a soil thermometer at a local nursery or hardware store. Or order one from a gardening catalog.

This table provides a good general guide for minimum soil temperatures for seeds and transplants.

Wayne McLaurin is a professor emeritus of horticulture with the University of Georgia College of Agricultural and Environmental Sciences.