Last Frost Date by Zone: What It Means and What You Can Plant Before It

Your last frost date is not the day it stops frosting. It is the date by which there is a 50 percent chance a freeze has already happened for the last time that spring, based on NOAA’s 1991 to 2020 climate normals. Half of all years, frost comes later than that date, sometimes weeks later, which is why it is a planning average and not a promise.

A more conservative number, sometimes called the 90 percent safe date, is typically about two weeks after the 50 percent date. In zone 6b, for example, the last frost date is April 15, but the 90 percent safe date is closer to April 29. Anyone planting tender crops like tomatoes or peppers on the 50 percent date is accepting real risk; waiting the extra two weeks cuts that risk sharply for very little lost season.

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Last frost by USDA zone

These are the representative dates used across this site’s planting calendars. Your own ZIP will usually land within a week or two of the zone figure, but the ZIP lookup above is exact.

Zones 11a and warmer do not have a meaningful last frost. Plan by the cool season instead: roughly November through February.

Notice how unevenly the season lengthens as the zone number climbs. Moving from 6b to 7a buys five days, but moving from 8b to 9a buys twenty-nine, and the gap widens again into the low double digits. Cold zones lose their frost-free window slowly at both ends, while warm zones gain it fast, which is part of why gardening advice written for zone 7 often does not translate cleanly to zone 9: the constraints are genuinely different, not just shifted by a few weeks.

Frost tolerant vegetables: what to plant before the last frost

This is the part most gardeners underuse. A hardy or half-hardy crop planted a month before your last frost date is not gambling, it is normal practice, and it often produces better than the same crop planted later into summer heat. The figure below is weeks relative to your last frost date, negative meaning before it, and it is a direct sow date unless the crop is marked transplant.

Use your zone’s last frost date from the table above to convert these into calendar dates. In zone 6b, for example, peas at 5 weeks before April 15 go in around March 11, and onions and broccoli transplant around April 1.

Potatoes and broccoli are listed half-hardy rather than fully hardy: a light frost does not touch them, but a hard freeze can knock back exposed foliage even though the plant usually recovers from below ground or from the crown. Treat their dates as reliable, not their leaves as invincible.

There is a second benefit to planting this group early that gets overlooked: these are mostly cool-season crops that bolt, turn bitter, or simply stop producing once real heat arrives. Lettuce and spinach sown at the normal warm-season pace, a few weeks after last frost alongside everything else, often bolt within a month in a zone 7 or warmer summer. Sown at 4 to 5 weeks before last frost instead, they get a full cool, productive run before that happens. The frost risk on the front end is smaller than the heat risk on the back end for most of these crops, which is the opposite of how people instinctively think about them.

If you are starting any of this group as transplants rather than direct sowing, a short hardening off period still helps even though the crop tolerates frost, since a seedling grown indoors under lights has not yet felt real wind or direct sun. It does not need the full outdoor transplant tolerance a tomato does, but a few days of acclimation before it goes in the ground reduces transplant shock regardless of species.

What must wait until after the last frost

Tender crops have no frost tolerance at all, and for most of them soil temperature matters as much as air temperature. Cold, wet soil rots seed and stunts transplants even when the air itself is not actually freezing anymore.

The extra week or two past the calendar date is not superstition. Warm-season seed germinates poorly, or rots outright, in soil below the mid 50s, and transplants of tomatoes and peppers sit and sulk rather than grow in cold soil even if the air temperature is fine during the day. Checking soil temperature with a cheap probe thermometer before you plant is more reliable than counting weeks on a calendar, especially in a spring that runs colder or wetter than average.

Corn and beans get a shorter buffer than the rest of the tender group, about a week rather than two, because both germinate from a larger seed with more stored energy and tolerate a slightly cooler soil than tomatoes or peppers do. That said, corn planted into soil below about 55 degrees germinates unevenly and can rot before it sprouts, so a week of buffer is a minimum, not a guarantee, in a spring that is running cold.

Can you have frost at 40 degrees

Yes, and this catches new gardeners every spring. The temperature on a weather forecast is measured about 5 feet above the ground, in a shaded, ventilated enclosure. The ground and the top of your plants are a different microclimate entirely.

On a clear, calm night, the soil and plant surfaces radiate their heat away into the sky faster than the surrounding air can replace it. That surface can end up several degrees colder than the air temperature the forecast reports. A forecast low of 38 to 40 degrees, if the sky is clear and there is no wind, can produce a real frost at plant level. The same forecast under cloud cover, or with a breeze mixing the air, usually produces nothing, because clouds trap outgoing heat and wind prevents the cold layer from settling at the surface.

Low spots make it worse. Cold air is denser than warm air and drains downhill the same way water does, pooling in the bottom of slopes, against solid fences, and in any low corner of a yard. If your garden sits in one of those spots, treat every forecast low under about 40 degrees in spring as a possible frost night, not just the ones that say 32 or below.

Dry air makes the same effect stronger. Moisture in the air slows radiational cooling because water vapor itself holds and re-radiates heat, which is part of why humid nights rarely frost even at a forecast temperature that would frost a dry night. This is one reason frost risk in spring can feel inconsistent from one clear, cold-looking evening to the next even when the forecast numbers look similar: the humidity and wind on the night in question matter as much as the number itself.

What one night of frost does

A tender crop caught by even a brief, light frost usually shows blackened, water-soaked leaves within a day, and for genuinely tender plants like basil, cucumbers and young tomato or pepper transplants, that damage is often fatal or close to it. A single hard freeze night can end a whole bed of unprotected tender transplants that had been growing well for weeks.

Hardy and half-hardy crops are unaffected by the same night, and some of them, kale and carrots especially, convert starch to sugar as a cold response and taste better afterward. That gap in tolerance is exactly why the earlier table is worth using: the crops on it are not fragile the way tomatoes are.

A partial exception is a very brief, mild frost right at freezing, where only the tips of a tomato or pepper’s top leaves blacken and the rest of the plant survives and keeps growing from lower nodes. That does happen, but it is not something to plan around. A transplant that looks fine the next morning can still have lost enough of its growing point to set it back by two or three weeks, and there is no way to tell in advance which frost will be mild enough to survive and which will not.

When to cover

Cover tender plants any night the forecast low is 36 degrees or below, because of the radiational cooling described above. Floating row cover or a simple sheet, supported on hoops rather than laid directly on the foliage, buys several degrees and is usually enough for a single light frost. For a hard freeze or a run of cold nights, a double layer of cover, a cold frame, or bringing potted plants indoors is safer than relying on fabric alone. The row cover versus frost blanket comparison has the weight-by-weight numbers if you are buying cover for the first time.

Why your last frost date may be wrong for your yard

The date on this page, and the one your ZIP code returns, comes from the nearest weather station’s thirty-year record, interpolated to your location. That is a good estimate, not a survey of your actual garden.

Microclimate is the biggest source of error. A south-facing bed against a brick wall, sheltered from wind, can run a full zone warmer than the open yard ten feet away. A low corner where cold air pools can run a full zone colder than the rest of the same property. Elevation matters too: gaining a few hundred feet of elevation over a short distance can push your last frost a week or more later than a valley location in the same zone.

Urban areas run warmer than the surrounding countryside, sometimes by several degrees, because pavement and buildings hold heat overnight. A garden in a city center can have a meaningfully earlier last frost than a rural station a few miles away that anchors the zone data. And simple distance matters: if the nearest reporting station is 20 or 30 miles away, in different terrain or near different water, treat the date as a starting point and adjust based on what you actually observe in your own yard over a season or two. Frost dates by city let you check a specific nearby location rather than relying on the zone average alone.

The practical fix is to keep your own record rather than relying on any published date alone. Note the date of the last frost you actually see in your yard for two or three springs running, along with where it showed up, and you will end up with a number that is more accurate for your specific garden than any station-based average could be. Until you have that record, treat the published date as the middle of a range, plant your hardy crops on the early side of it, and hold your tender transplants until a week or two past it unless you are prepared to cover them.

Where to go next

• When to start seeds indoors by zone
• Hardening off seedlings: the schedule
• First frost date and frost protection
• USDA planting zones explained