When to Plant Vegetables by Your Last Frost Date

What the last frost date really means

A last frost date is not a promise. It is a probability worked out from 30 years of temperature records. NOAA's National Centers for Environmental Information (NCEI) publish these dates for thousands of weather stations as part of the U.S. Climate Normals. The current set covers 1991 to 2020.

Each station gets a table. For spring, the table gives the date by which the last cold night of a given temperature has passed in a given share of years. The NCEI heading reads "probability of later date in spring than indicated". A 90% date is early: in 9 springs out of 10, the cold came later than that. A 50% date is the median. A 10% date is late: a later cold night happened in only about 1 spring in 10.

The tables also come in several temperatures. NC State Extension, which explains how to read them, gives these definitions:

• Freeze: the air falls below 32 °F.
• Hard freeze: the air dips below 28 °F.
• Frost: it depends on humidity as well as temperature, so there is no single threshold. NCEI's tables use 36 °F as the temperature linked to frost.

Here are the spring rows for one station, Rochester International Airport, Minnesota, at 1,304 feet. This guide uses the same station for every example below.

Read the 32 °F row like this. In half of the springs from 1991 to 2020, the last freeze at this airport came after April 30. In about one spring in ten, it came after May 13. That is 13 days later than the median. The 36 °F frost row runs 9 days behind at the median: May 9.

Which column should you plan with? NC State Extension gives a simple rule for spring and fall dates. The 10% date is "high precision, low risk", for risk-averse decisions. The 90% date is "low precision, high risk", for aggressive ones. The 50% date sits in between. In garden terms: plant tender crops after the 10% date if losing them would hurt, and gamble on the 50% date only with a row cover or spare plants ready.

How to find your own date

Look up the date for a station near you instead of copying one from a seed catalog or a zone chart. Three official places, from quickest to most detailed:

1. The last spring freeze map. NOAA's Climate.gov published an interactive map of the average last spring freeze across the lower 48 states. Each dot is a station. It shows the date when the chance of freezing temperatures drops below 50 percent, based on the 1991 to 2020 normals. The page is now archived and no longer updated, but the dates are the same normals.
2. The NCEI normals search. The map shows only the 50% date. The same normals also hold the dates when the chance drops below 40, 30, 20 and 10 percent. Climate.gov points to NCEI's Annual/Seasonal Normals search for those, where you can look up a single station.
3. Your state. Many National Weather Service offices and state agencies post the station tables as PDFs. The Rochester table above comes from the Minnesota Department of Natural Resources, which publishes NCEI's summary for Minnesota stations.

Two choices make the number fit your garden better:

• The station. Choose one close by and at a similar elevation. NCEI lists each station's elevation, and the map's background colors between stations are interpolated estimates, not measurements.
• The threshold. Note whether the date is for 32 °F or 36 °F. NCEI's last spring freeze map uses 32 °F. If a source just says "last frost", find out which one it means.

Remember the limits, too. NCEI says each year's actual conditions "may widely vary" with the weather patterns, and the map is a guide, not a forecast. In spring, check the local forecast on weather.gov before you set out anything tender.

Hardiness zones are not frost dates

It is tempting to time planting by your USDA zone. The zone answers a different question. In USDA's own words, the Plant Hardiness Zone Map is "based on the average annual extreme minimum winter temperature". It shows how cold the coldest winter night typically gets, in 10 °F zones from zone 1 (coldest) to zone 13 (warmest). Each zone splits into an "a" and a "b" half of 5 °F.

What the 2023 edition tells you, from USDA's pages:

• It is based on 1991 to 2020 weather data, and on "the average lowest temperatures, not the lowest ever". A rare cold snap can still go below it.
• USDA says all its zone maps "should serve as general guides for growing perennial plants". The zone numbers in nursery catalogs are for perennials.
• Across much of the country the 2023 map is about a quarter-zone warmer than the 2012 map, which USDA puts down mainly to the newer 30-year period. Because the zones average the single coldest night of each year, USDA adds that changes in zones "are not reliable evidence of whether there has been global warming".

What it does not tell you: when the last spring frost or the first fall frost usually comes. USDA's guide to the map does not mention frost dates or planting dates at all. It lists other factors that matter for plant survival, such as wind, soil moisture, humidity and summer heat. Vegetables sown in spring and harvested before winter never meet the coldest night of the year, the one the zone describes. For them, the frost date table above is the number to plan with.

Planting schedule: weeks before and after the last frost

The University of New Hampshire (UNH) Extension publishes a fact sheet that does exactly what this guide needs. For each vegetable it gives the time from seed to transplant and when the plant is safe to set out, in weeks before or after the last frost. Its method: mark the planting date on a calendar and count back the seed-to-transplant weeks to get the sowing date.

The table below copies UNH's weeks and applies them to the example station's 50% date, April 30 2027. The sowing window counts the seed-to-transplant weeks back from the first day you could set the plants out. Swap in your own frost date and every date moves with it.

Some vegetables are usually sown straight into the garden. UNH times them by the frost date or by the soil temperature:

UNH notes that cucumbers, squash, zucchini and pumpkins can go either way: start them indoors for 3 to 4 weeks, or sow them outside once the soil reaches 70 °F. A soil thermometer gives that answer better than any calendar.

One caution before you use these weeks. UNH wrote them for New Hampshire and says Memorial Day is "a conservative estimate" of the last frost date for the center of the state. So the weeks were meant to be counted from a cautious date, not a median. If you count from your 50% date, as in this table, tender crops land earlier than UNH intended. The next section shows the difference.

Other extension services publish slightly different numbers. University of Maryland Extension, for example, gives 5 to 6 weeks indoors for tomatoes and 8 to 10 weeks for peppers, eggplants and onions. It also warns that a common mistake is to sow seeds too early, which gives "tall, root-bound plants". When two sources differ, that warning is a reason to lean toward the shorter time.

Worked example: a calendar from one date

Take three crops at the Rochester station and plan them twice: once from the 50% date (Apr 30), once from the cautious 10% date (May 13).

The tomato math, step by step:

Notice what the two frost dates do. Planting tomatoes 1 to 2 weeks after the 50% date puts them in the ground around May 7 to May 14, which reaches the 10% date of May 13. So following UNH's "weeks after" from the median already buys most of the safety margin. Broccoli and the other cool-season crops in the table go out weeks before any of these dates, because UNH times them before the frost.

The hardening-off line comes from University of Maryland Extension: begin hardening transplants 1 to 2 weeks before you set them out. Put them in a shaded, sheltered spot on warm days and bring them in at night, giving them a little more sun each day. Maryland adds a few limits:

• Do not put tender seedlings outside on windy days or below 45 °F.
• Water less often to slow growth, but do not let the plants wilt.
• Cucumbers and melons stop growing if hardened too hard. They may stay out overnight only if it will not fall below 50 °F.

Two date tools make this quick for your own garden. The add or subtract days calculator takes your frost date and adds or subtracts the weeks for each crop. The days between dates calculator answers the reverse question: how many weeks are left from today to your sowing date or your frost date.

A light check for indoor seedlings

Early sowing dates fall in late winter, when days are still short. University of Maryland Extension says natural light from a window is "seldom enough" for strong seedlings. It recommends grow lights 2 to 6 inches above the plants, lit for 14 to 16 hours a day on a timer.

At the Rochester station, the first pepper sowing date, March 5, has 11 h 23 min from sunrise to sunset. The day there does not reach 14 hours until April 27, after most indoor sowing is done. Check your own place and date in the sunrise and sunset calculator, which shows the day length.

Season length and the first fall frost

The same NCEI tables give the first fall freeze, read the other way round: the probability of an earlier date in fall. At the Rochester station, the 50% date for 32 °F is October 6, and the 10% date is September 22.

From the median last spring freeze to the median first fall freeze is 159 days. From the 10% spring date to the 10% fall date, the cautious season, it is only 132 days. The tables also list the freeze-free period directly, as a probability of a longer period: at 32 °F there is a 50% chance of more than 159 days and a 90% chance of more than 140 days. Count your own season between any two dates in the days between dates calculator.

The season length is what you compare with how long a crop needs in the garden. UNH's rutabaga entry is the one crop in its list timed by the calendar instead of the spring frost: sow it from mid-June to mid-July.

Put the dates in your planner

Once the dates are worked out, write them down where you will see them in February. The free garden planner has a yearly task calendar whose month boxes are left empty on purpose, because sowing dates depend on where you live. This guide gives you the dates to fill them with:

1. Look up your station's 32 °F and 36 °F spring dates at 50% and 10%.
2. Decide which one you plan from. For tender crops, the 10% date, or the 50% date plus the weeks after the frost that UNH gives.
3. Use the schedule table to work out a sowing date and a set-out date for each crop, starting with the longest ones, such as onions, celery and peppers.
4. Add a hardening-off reminder 1 to 2 weeks before each set-out date.
5. In spring, compare the plan with the 7-day forecast before planting anything tender.

Then keep your own record. Write down the date of the last frost you actually saw in your garden each spring, next to the station's dates. After a few years you will know whether your yard runs earlier or later than the station, and the plan gets better every season.

Frequently asked questions

Sources

• Nelson, El-Khoury and Boyette, Interpreting Freeze / Frost Probabilities from the National Centers for Environmental Information, NC State Extension publication AG-873 (published February 28, 2020; revised December 11, 2024)
• NOAA National Centers for Environmental Information, Summary of Annual Normals 1991-2020, freeze data for Rochester International Airport, MN (USW00014925), generated May 2, 2024, as published by the Minnesota Department of Natural Resources
• NOAA National Centers for Environmental Information, When to Expect Your Last Spring Freeze (updated March 22, 2024, with the 1991-2020 normals)
• NOAA Climate.gov, Interactive map: average date of the last spring freeze across the United States (April 17, 2025; archived page)
• NOAA National Centers for Environmental Information, U.S. Annual/Seasonal Climate Normals 1991-2020 data search
• USDA Agricultural Research Service, Plant Hardiness Zone Map 2023: How to Use the Maps
• USDA Agricultural Research Service, Plant Hardiness Zone Map 2023: Map Creation
• University of New Hampshire Extension, Growing Vegetables: When to Plant Your Vegetable Garden (fact sheet)
• University of Maryland Extension, Starting Seeds Indoors (updated August 14, 2026)
• University of Maryland Extension, Hardening Off Vegetable Seedlings for the Home Garden (updated February 20, 2023)
• NOAA Global Monitoring Laboratory, Solar Calculation Details (equations used for the day lengths on this page)

Written by Tobias. Updated October 21, 2026.