Last Frost Date By Zone: How to Find It and Use It for Planting

The last frost date is the single most useful number in gardening and also the most misunderstood. It’s not a guarantee. It’s not the day you should plant everything. It’s a 50% probability marker, half the years in your area, the last frost falls after that date, not before it.

Treating it as a hard deadline is how people lose seedlings to a late cold snap. Treating it as useless because “it’s just an average” is how people plant too late and lose weeks of growing season. Here’s how to actually use it.

Finding your last frost date

The fastest way is a zip code lookup, the Old Farmer’s Almanac frost date tool and the NOAA Climate Prediction Center both give you a date based on decades of local weather station data. Search your zip code and you’ll get three numbers: a 90% probability date (frost is very unlikely after this), a 50% probability date (the commonly cited “last frost date”) and a 10% probability date (frost is rare but not impossible after this).

Most gardening advice, including this site, uses the 50% date. That framing matters, it means roughly half of all years, you’ll still get a frost after that date.

Why the 50% number isn’t a planting deadline

If your last frost date is April 15, that doesn’t mean April 16 is safe. It means that historically, about half the time, your last frost happened before April 15 and about half the time, it happened after. Some years you’ll get lucky. Some years a frost lands in late April and takes out anything you planted too confidently.

The practical takeaway: use the last frost date to plan your seed-starting schedule, but don’t transplant tender plants outside the moment the date passes. Check a short-range forecast in the week leading up to your planned transplant date and hold off a few extra days if anything colder than 40°F is showing up in the forecast.

Using your frost date to plan planting

This is where the last frost date actually earns its keep, not as a transplant deadline, but as the anchor point for everything else. Once you have it, seed starting for every plant on your list gets scheduled backward from it, tomatoes 6-8 weeks before, onions 10-12 weeks before and so on.

It also tells you when to direct sow cold-tolerant crops. Peas, spinach and radishes can go into the ground 2-4 weeks before your last frost date, not after, these plants tolerate light frost and actually prefer cooler soil for germination.

Frost tolerance by plant

Not every plant reacts to a late frost the same way. Roughly:

• Hardy, survives a light frost: peas, spinach, kale, broccoli, cabbage, lettuce, onions
• Half-hardy, tolerates a light frost, damaged by a hard freeze: carrots, beets, potatoes
• Tender, killed by any frost: tomatoes, peppers, cucumbers, squash, beans, basil, melons

If a late frost is forecast and you’ve already transplanted anything from the tender category, covering plants overnight with a sheet, row cover, or overturned bucket is usually enough to get them through a light frost. It won’t save them from a hard freeze.

First frost matters too

Your last spring frost date has a counterpart in fall, the first frost date, which marks the average start of the danger period at the other end of the season. The gap between the two is your frost-free growing season length. Knowing both numbers lets you count backward from fall for anything that needs a set number of days to mature, not just forward from spring.

Common mistakes

• Using a regional date instead of a local one: Frost dates vary meaningfully within the same city depending on elevation, proximity to water and whether you’re in a low-lying area where cold air pools. A zip code lookup gets you close; a few seasons of your own observation gets you exact.
• Planting everything the day after the date passes: Tender crops especially benefit from waiting a week or two past your 50% date, particularly in a year where the season has been running cold.
• Ignoring microclimates in your own yard: A spot against a south-facing wall can be measurably warmer than an open bed 20 feet away. If you’re pushing the timing on tender plants, that’s the spot to use.

For how this date fits into the rest of your spring planting schedule, see the spring gardening guide.

Editor’s Note: Parts of this guide were structured and optimized with the assistance of AI, then thoroughly reviewed, edited and expanded with first-hand growing experience by our author Raymond to ensure practical, real-world accuracy.