What is a frost date and where does it come from?
First and last frost dates are averages worked out from many years of weather station records. A last spring frost date is the point after which frost becomes unlikely, and a first fall frost date marks when it becomes likely. Because they are averages, frost can and does show up on the wrong side of them.
Agencies and universities often publish frost date tools by location. These are a starting point, and the exact numbers vary by source and by which probability level they use, so check how a given tool defines its dates.
Why does your own yard differ from the chart?
The nearest weather station may sit in a town, at a different elevation, or on a warmer surface than your field. Cold air pools in hollows, so a garden at the bottom of a slope can freeze while one higher up stays clear. Open sky on a still, clear night lets heat escape quickly.
Your own thermometer, placed at plant height in the spot you actually grow, is worth more than any regional table. Note the lowest overnight reading on questionable nights.
- Clear, calm nights are the most frost-prone
- Low ground freezes before higher ground
- Wet soil and nearby water can slightly moderate cold
- A thermometer at plant height tells you what the plants feel
How should you use frost dates for planting?
Think in groups. Hardy crops, such as many leafy greens and peas, tolerate light frost and can go in before the last-frost average. Tender crops, including tomatoes, peppers, squash and beans, should wait until frost risk has clearly passed and soil has warmed.
A simple margin helps: plant tender crops a week or two after your average date, or protect them if you go earlier. In fall, count backward from the first-frost average to check that late crops have time to finish.
What do the words light frost and hard freeze mean?
A light frost damages the most tender leaves while many hardy plants shrug it off. A hard freeze, meaning several hours at a colder temperature, kills a wider range of plants and can damage fruit blossoms and young shoots. Different plants have different thresholds, so extension publications for your crop are the right place to look.
Frost forecasts from the National Weather Service are usually issued as frost advisories or freeze warnings. Learn how your local office words them.
How do you build a safety habit around forecasts?
In the weeks around your frost dates, check the evening forecast every day. Know your response in advance: where the row cover is, which pots to carry inside, which animals need extra shelter or water that will not freeze.
Write down what happened each year. A short note about the date and the temperature that damaged a plant helps you tune your own dates and tells you which plants in your garden are the tender ones.
- Keep covers and old sheets ready before the warning arrives
- Water soil lightly before a cold night if dry, since moist soil holds heat a bit better
- Record each frost event with date and plant damage
What should you do if frost arrives early or late?
Even with good planning, a surprise frost will eventually come. If tender plants were hit, do not rush to cut them back. Damaged tissue sometimes shields lower growth from further cold, and many plants resprout from lower buds. Wait until new growth shows what is alive.
If a crop is lost, replant if time allows, using a faster-maturing variety. Note the date, because every surprise improves your local knowledge.
- Wait for new growth before pruning damaged plants
- Replant quick-maturing varieties if time remains
- Record the date and the damage
Where can you find frost information you can trust?
The National Weather Service posts forecasts and frost and freeze products for your area, and your state university extension service publishes planting guides written for local conditions. State climatologists may also share climate summaries. Use more than one source and compare, since tools can differ by definition and years of data used.
Be wary of sources that give a single exact date with no explanation. A trustworthy guide explains that it is an average and tells you how it was made.
Key takeaways
- Frost dates are averages, so frost can arrive after the last date and before the first.
- Your microclimate can differ from the nearest station by a lot.
- Group crops as hardy or tender and plant tender ones with a margin.
- Check forecasts nightly near your frost dates and have covers ready.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Rural Farm Life Editorial Team. See our editorial policy.