Frost Date Tool

Two dates shape almost every vegetable garden: the average last frost in spring and the average first frost in fall. Between them lies your frost-free growing season. This frost date tool turns those two dates into the information you actually plan with: how long your season is, when cool-season crops can go out, when it is safe to plant tender crops such as tomatoes and peppers, and the last practical sowing dates for common fall crops.

Enter your own frost dates for the most accurate results. If you do not know them yet, the guidance below explains where to find them.

How to use the frost date tool

1. Enter your average last spring frost date.
2. Enter your average first fall frost date.
3. Choose a safety margin for tender crops. A week or two after the last frost lowers the risk of losing tomatoes, peppers, basil and squash to a late cold night.
4. Read your results: the number of frost-free days, key planting dates, and last sowing dates for fall crops.

For a crop-by-crop schedule, use the planting calendar. For indoor seed starting dates, use the seed starting calculator.

Where to find your frost dates

• Your state Cooperative Extension service often publishes frost dates and planting calendars by county or region.
• Frost date lookups by ZIP code, offered by many seed companies and gardening sites, use records from nearby weather stations.
• The National Weather Service and NOAA climate normals provide long-term temperature records for weather stations across the country.
• Experienced local gardeners and garden clubs often know how local conditions differ from official records.
• Your own notes. Recording the actual last and first frost in your garden each year is the most accurate source of all, after a few seasons.

Choose a weather station close to your garden and similar in elevation. A station on a hilltop, in a city center or beside a large lake can have frost dates quite different from a garden a few miles away.

What “average” really means

An average frost date is not a guarantee. It is typically the date around which frost later in spring (or earlier in fall) is roughly as likely as not. In some years the last spring frost comes two or three weeks before the average; in others, a week or two after.

Many frost date sources also publish dates at different probabilities, for example the date after which there is only a 10 percent chance of frost. Using a lower-risk date for tender crops is a sensible way to avoid losses. The safety margin option in the tool does something similar, adding a week or two before tender crops go out.

Understanding your growing season

The number of frost-free days between your two frost dates is your growing season length. It shapes which crops and varieties you can grow.

Planting around your frost dates

Cool-season crops: before the last frost

Peas, spinach, radishes, lettuce, kale, onions and potatoes tolerate light frost. Many can be sown or planted from about four to six weeks before the last spring frost, as soon as the soil can be worked. Getting them in early lets them mature before summer heat makes them bolt or turn bitter.

Tender crops: after the last frost

Tomatoes, peppers, eggplant, basil, beans, corn, cucumbers, squash and melons are damaged or killed by frost, and they grow poorly in cold soil even without frost. Plant them after the last frost date, ideally once nights stay reliably above about 50°F. Waiting an extra week often gives faster growth than planting into cold ground.

Fall crops: counting back from the first frost

For fall harvests, count back from your first fall frost. The tool does this for common crops, using each crop’s days to maturity plus extra time for slower growth as days shorten. Tender crops need to finish before frost, so their deadline is earlier. Frost-tolerant crops such as kale, carrots, spinach and radishes can be sown later, because they keep growing through light frosts.

Worked examples

A moderate to long season

With a last spring frost around April 20 and a first fall frost around October 20, the season is about 183 frost-free days. Peas and spinach can go in from around early March. Tomatoes and peppers go out from late April or early May. The last sensible sowing of bush beans for a fall crop is around the end of July, and kale can be sown until about mid-August.

A short northern season

With a last frost around May 25 and a first frost around September 15, the season is only about 113 days. Tomatoes and peppers go out in early June, and should be varieties that mature quickly. Fall sowing deadlines arrive early: bush beans by late June, and kale by about mid-July. Cool-season crops, which thrive in long, mild northern summers, become especially valuable.

Protecting plants from frost

A few simple methods can save plants on a cold night and extend the season at both ends.

• Row cover: lightweight fabric over hoops traps ground heat and can give several degrees of protection.
• Sheets and blankets: cover plants in the evening and remove covers in the morning. Avoid plastic touching leaves, which can conduct cold.
• Cloches and buckets: overturned buckets, milk jugs with the bottoms removed, or purpose-made cloches protect individual plants.
• Cold frames: boxes with clear lids extend the season for greens by weeks.
• Water first: moist soil holds more heat than dry soil, so watering before a frost can help.
• Harvest before a hard freeze: pick tender crops such as tomatoes and peppers when a hard freeze is forecast. Mature green tomatoes ripen indoors.

Frost, freeze and hard freeze

These terms are often used loosely, but they mean different things for plants. A light frost, around 32°F at ground level on a clear, still night, damages tender plants such as basil and tomatoes but barely affects cool-season crops. A hard freeze, often described as several hours at around 28°F or below, kills most tender plants and damages many hardier ones. Kale, collards, Brussels sprouts, carrots, parsnips and leeks often survive into the low 20s°F, especially under row cover.

Frost is most likely on clear, calm nights, when heat radiates away from the ground. Cloudy or windy nights are less likely to produce frost even when temperatures are similar.

Keep your own frost records

Over a few years, your own observations become more useful than any published average. Note the date of the last spring frost and the first fall frost in your garden each year, along with which plants were damaged. You may find your garden runs a week earlier or later than the nearest station, especially if it sits in a frost pocket or a sheltered, warm spot.

Frost pockets and microclimates

Cold air is heavier than warm air, and on clear, still nights it flows downhill and collects in low spots, much like water. Gardens at the bottom of a slope, in a valley or in a hollow can get frost on nights when gardens a short distance uphill stay clear. These frost pockets can have a last spring frost a week or more later than the surrounding area.

The opposite also happens. Gardens near south-facing walls, paved areas, large bodies of water or in the middle of a town often stay a few degrees warmer at night. If you notice that frost hits your garden earlier or later than the published dates, adjust the dates you enter into the tool to match your own experience.

Extending the season

Season extension lets you plant earlier in spring and harvest later in fall, effectively lengthening your frost-free season.

• Row cover: lightweight fabric supported on hoops. Easy to use and adds a few degrees of protection on frosty nights.
• Low tunnels: clear plastic over hoops, vented on sunny days. They warm soil earlier in spring and protect greens into late fall.
• Cold frames: boxes with clear lids, ideal for hardening off seedlings and growing winter greens.
• Black plastic mulch: laid on beds a week or two before planting, it warms soil for heat-loving crops such as melons and peppers.
• Walls of water: water-filled plastic sleeves around individual tomato plants store heat during the day and release it at night.

Even simple season extension can add several weeks to each end of the season, which matters most where the frost-free season is short.

Matching crops to your season length

Compare each crop’s days to maturity with your season length. Crops that need most of the season, such as winter squash, melons and late tomatoes, need a prompt start and often a transplant head start. In a short season, choose varieties with shorter days to maturity, and lean on quick crops that can be sown more than once. The harvest date calculator shows when a planting should be ready, and the plant database lists days to maturity for common crops.

Using frost dates with other tools

Once you know your frost dates, the rest of the planning tools on the site become more useful. The seed starting calculator counts back from your last frost to indoor sowing dates. The planting calendar builds a complete spring and fall schedule. The gardening calendar lists every garden job month by month. Enter the same two dates in each, and your whole garden year lines up.

Frequently asked questions