What Is a Frost Date, and How Should You Use It?

Your last frost date is the average date of the last freezing night in spring. Your first frost date is the average date of the first freezing night in fall. The days between them make up your growing season.

A frost date is a coin toss

Frost dates published by NOAA and Extension offices are usually the date with a 50% chance of frost on a later day. In other words, in about half of all years you will still get a frost after your last frost date.

That is why most planting advice for tender crops says “after your last frost” rather than “on” it.

How gardeners use frost dates

• Starting seeds indoors. Seed packets count backward from the last frost date. Tomatoes are usually started 6 to 8 weeks before it.
• Planting tender crops. Tomatoes, peppers, squash and basil go out after the last frost, once nights stay above 50°F.
• Planting hardy crops. Peas, spinach, onions and many brassicas tolerate light frost and can be planted weeks before the date.
• Fall planning. Counting back from the first fall frost tells you the latest date to plant a crop that needs, say, 60 days to mature.

Where to find yours

Your county Cooperative Extension office publishes frost dates for local weather stations. Frost dates can differ by a week or more within a few miles, depending on elevation and whether you live in a low spot where cold air settles.