When is the last frost date where I live, and how do I find it?
Short answer: Your last frost date is a statistic from 30 years of weather records, not a forecast. The commonly quoted 'average' date is the 50% date, so a later frost still happens about 1 year in 2. The 10% date, often about 2 weeks later, is the safer choice. Find yours through your state's university extension or NOAA climate data.
What does “last frost date” actually mean?
It is a statistic from past weather, not a forecast. NOAA’s National Centers for Environmental Information (NCEI) calculates freeze dates from 30-year records at weather stations.
NC State Extension explains that NCEI tables list the last spring date for several temperatures at probability levels from 10% to 90%. For spring, the probability is the chance that a frost or freeze occurs on or after that date. In NC State’s Raleigh example, the 50% frost date is April 12 and the 10% date is April 26.
| Probability level | What it means | Risk if you plant then |
|---|---|---|
| 90% date | A later freeze happens about 9 years in 10 | High (aggressive) |
| 50% date | A later freeze happens about 1 year in 2 | Moderate |
| 10% date | A later freeze happens about 1 year in 10 | Low (conservative) |
When a seed packet or website says “average last frost,” it usually means the 50% date. That date is a coin flip.
Purdue Extension gives a concrete example from Indiana. Its map shows dates with a 10% chance of a later 32°F night. About two weeks earlier, that chance rises to 50%.
What temperature counts as frost or freeze?
NC State Extension lists the thresholds used in NCEI tables:
| Term | NCEI threshold (air temperature) |
|---|---|
| Frost | 36°F |
| Freeze | Below 32°F |
| Hard freeze | Below 28°F |
NC State calls these three the most important thresholds for agriculture.
Frost depends on humidity as well as temperature. You can have a freeze without visible frost, or frost without a freeze. Plants in low, open spots can get colder than the nearby station reading. For covering plants on a cold night, see how to protect plants from frost.
How do I find the last frost date for my area?
- Check your state’s university extension. Most land-grant universities publish frost dates or planting calendars for their state. Search “[your state] extension last frost date” or “planting calendar.”
- Use the nearest weather station, not just your ZIP code. Dates shift with elevation, nearness to water and valley location. Cold air settles in low spots.
- Look at NOAA climate data. NCEI publishes U.S. Climate Normals for thousands of stations. The current normals cover 1991 to 2020. NCEI offers a Quick Access tool, a full Data Access tool with station search, and bulk CSV downloads. NC State notes that its freeze-probability tables were based on 1981 to 2010 data when written, so check which period any table uses.
- Try regional climate centers. NC State points to the Midwestern Regional Climate Center freeze maps and Southeast Regional Climate Center station summaries.
- Note which probability you are reading. Write down both the 50% and 10% dates if they are listed.
Your hardiness zone is a different number. It describes winter low temperatures, not spring frost timing. See USDA hardiness zones.
How long after the last frost should I plant?
Purdue Extension groups vegetables by cold tolerance:
| Crop group | Purdue description or examples | When to plant |
|---|---|---|
| Hardy | Tolerate hard frost | Can go in before tender crops |
| Semi-hardy | Tolerate light frost | Can go in before tender crops |
| Tender | Bean, tomato, sweet corn | After the average last frost; nights at least 50°F |
| Very tender | Cucumber, pepper, squash, melons | At least 2 weeks after the average last frost; nights 60-65°F |
Purdue also says warm-season crops need soil of at least 60°F. Tender crops may still need frost protection after planting.
A cautious approach: hardy crops can usually go in around the 50% date. Wait for the 10% date, or roughly 2 weeks later, for tomatoes, peppers and squash. Then check the 10-day forecast before you set plants out.
Quick answers
What is the average last frost date? It is usually the 50% date. There is still about a 50% chance of a freeze after it.
Is it safe to plant on the last frost date? For hardy crops, generally yes. For tender crops, the 10% date or about 2 weeks later is safer.
Is 36°F cold enough for frost? It can be. NCEI tables use 36°F (air temperature) as the frost threshold, since frost can form on plants even when the air reading is above 32°F.
What is a hard freeze? Air temperature below 28°F, by the NCEI threshold NC State describes.
Does my hardiness zone tell me my frost date? No. Zones describe winter lows. Look up frost dates separately through your extension service or NOAA data.