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Regional Calendars, Climate & DataLate Spring Frost Risk Calendar
Frost after planting is one of the most common causes of crop loss. A frost risk calendar turns that risk into a plan: when you start taking chances, when you play it safe and what you keep on hand.
Key points
- Your average last frost date is a midpoint, not a safe date.
- Group crops by frost tolerance and plant in bands around the date.
- Cover before sunset and let covers reach the ground.
- Wait a few days before judging frost damage.
What is a last spring frost date, really?
A published last spring frost date is an average from past records at a weather station. It means that in about half the years the last frost came after that date, and in about half it came before. It is not a safe date, and it is not a guarantee.
Some sources also give dates for lower or higher chances, which help you choose your risk level. Ask your extension office for frost-probability tables for your county, or check NOAA National Centers for Environmental Information and the National Weather Service for station data.
Pay attention to the trend as well as the date. If the last three springs each produced a frost later than the average, your site may be running colder than the station, and your own log should outweigh the table.
What is the difference between frost and a freeze?
Frost is ice forming on surfaces when the air near the ground cools to freezing, usually on clear, calm nights. A freeze is when the air temperature itself drops to or below freezing, which can occur with wind and cloud. Tender plants can be hurt by both, but a hard freeze is more damaging than a light frost.
Crops differ widely in how much cold they tolerate. Hardy crops such as spinach and kale handle light frost, while tomatoes, peppers, squash and beans are damaged easily. Check extension crop guides for the tolerance of each crop you grow.
- Calm, clear nights carry the highest frost risk
- Wind and cloud cover reduce frost but not freezes
- Tolerance varies by crop and growth stage
How do you build a risk calendar?
Think in bands. Start with the date for your average last frost and look at the dates before and after it. Hardy crops can go in during the band before the average date, semi-hardy crops near it and tender crops after it, with a safety margin you choose.
For example, if your average last spring frost falls in early May, you might plant tender crops a week or two after that date, or earlier with protection ready. That is an illustration of the method and not a recommended date for your site.
A second tool is the frost-free test row. Plant a small amount of a tender crop a week or so earlier than the main planting, protected and labeled, and track how it fares.
What should you watch before planting tender crops?
Look at the extended forecast, and in the days after planting watch the overnight lows, wind and cloud cover. A forecast of a clear, calm night after a cold day is a warning. Local low spots frost first, so know your own cold pockets.
Also read soil temperature, because warm-season crops grow poorly in cold soil even when frost is not forecast. Plant when both soil and forecast agree.
How do you protect plants on a frost night?
Cover plants before sunset with frost cloth, row cover, buckets or blankets, and let the cover reach the ground so that it holds soil heat. Avoid plastic touching leaves, since it can transmit cold. Watering the soil in the afternoon can help it hold heat, but follow local water rules.
Remove covers the next morning when temperatures rise. For larger plantings, ask your extension office about options such as irrigation-based or heater-based protection, which have costs and rules and need careful management.
Fruit trees, berries and perennials face frost at bloom, when a few degrees matter. Ask your extension office about local bloom dates and protection options for your crops, since cultivars differ in how early they bloom.
How do you assess frost damage?
Damage often shows a day or two later as blackened, water-soaked or wilted leaves. Wait a few days before cutting or replanting, because some plants regrow from undamaged growing points. Check growing points, stems and new leaves.
For field crops, ask a crop adviser how to evaluate stand and growing point injury before replanting, and talk to your insurance agent about replant provisions. Keep dated photos and notes.
Take photos and notes of any damage, with the date and the overnight low, for your records and for insurance conversations.
What mistakes should you avoid?
Trusting a warm week, ignoring cold pockets, setting out unhardened transplants and covering too late are the usual errors. Another is removing covers too early on a cold morning.
Keep notes each spring on the actual last frost, the nights you covered and what survived. Your log will improve your risk calendar year after year.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.