The Best Temperature for Vegetable Plants

Cool-season vegetables die in hot, summer weather.

Successful vegetable gardening depends in part on properly timing planting and growing activities according to seasonal temperatures. Vegetables vary widely in ideal growing temperatures, but fall in to one of two main categories.

Types

All vegetables qualify as either cool-season or warm-season crops, depending on their ideal temperatures for best growth. Cool-season vegetables such as broccoli, cauliflower and lettuce do best in temperatures of 60 to 80 degrees F, while warm-season choices such as peppers, cucumbers and tomatoes grow well with daytime temperatures of 70 to 95 degrees F.

Soil Temperature

Soil temperature is the real key in seed germination and growth, although air temperature affects soil temperature, along with affecting plant health after seeds germinate and sprout. Very hardy vegetables like kale and lettuce germinate at soil temperatures as low as 40 degrees F. Other cool-season varieties require soil temperatures of at least 50 degrees F. At 60 degrees F, most cool-season and many warm-season vegetables germinate, while others, including squash and corn, need soil of 70 degrees F or more.

Time Frame

Hardy vegetables survive planting four to six weeks before the last frost date for your location while frost tolerant ones need planting no earlier than three weeks before this date. Waiting until the frost date for tender vegetables and one to two weeks after for warm-season ones results in the best growth and highest yields.

References

• Oregon State University Extension: Soil Temperature is Key to the Timing of Vegetable Planting
• University of Illinois Extension: Planting--Vegetable Gardening
• Colorado State University Extension: Vegetable Planting Guide

Resources

• North Carolina Cooperative Extension: Growing a Fall Vegetable Garden
• North Carolina Cooperative Extension: Home Vegetable Gardening