Frost Date & Growing-Window Calculator & Will It Finish Before Frost?
Times the season for tomatoes
Find your frost-free season length from the last spring and first autumn frost, and check whether a crop's days to maturity fits before frost — with the latest safe sow-by date and a year-strip view.
Your frost-free season runs 20 Apr to 20 Oct (183 days). A 90-day crop fits with 93 days to spare — sow any time from 20 Apr, and by 22 Jul at the latest to beat the autumn frost.
Next: stagger sowings between the earliest and sow-by dates for a longer harvest, and add a 1–2 week safety margin — frost dates are averages and vary year to year.
Preset frost dates are typical examples — use your local last/first frost dates for accuracy.
Frost & growing window — key facts
- Frost-free season
- first autumn − last spring frost
- Crop fits if
- days to maturity ≤ frost-free days
- Sow-by date
- first frost − days to maturity
- Safety margin
- add 1–2 weeks each end
- Frost-tender
- tomato, maize, beans, cucurbits
- Frost-hardy
- wheat, peas, brassicas, onion
- Extend season
- transplants, covers, early varieties
- Privacy
- Runs in your browser; nothing uploaded
Fit the crop to the frost-free window
Every frost-tender crop has to grow, flower and ripen between the last killing frost of spring and the first of autumn. Count the days between those two dates and you have your frost-free season; compare it with a crop's days to maturity and you instantly know whether it can finish. The tool also works backwards to the sow-by date — the last day you can plant and still beat the autumn frost — and shows the whole picture on a year strip with the crop's growing bar laid over the frost-free window.
This is the difference between a full harvest and a field of unripe produce caught by an early frost. If a crop is too long for your season, the fixes are practical: pick an 'early' short-season variety, raise transplants indoors to bank a few weeks, warm the soil, or protect the ends of the season with row covers and tunnels. Frost dates are averages, so build in a margin, and pair this with the Growing Degree Days tool where warmth — not just calendar days — is the limiting factor.
Check the fit
See at a glance whether a crop matures inside your frost-free season.
Find the sow-by date
Know the last day to plant and still harvest before autumn frost.
Plan succession
Stagger sowings between the earliest and latest dates for a longer harvest.
Beat short seasons
Spot when you need early varieties, transplants or season-extending covers.
Frequently Asked Questions
How do I find my growing season length?+
Count the days between your last spring frost and your first autumn frost — that's the frost-free season. For example, 20 April to 20 October is about 183 frost-free days. Enter your two frost dates (or pick a climate zone) and the tool calculates it and checks whether your crop fits.
Will my crop finish before the first frost?+
Compare the crop's days to maturity with your frost-free season length. If maturity ≤ frost-free days, it fits — with the difference as 'slack'. If it's longer, the crop won't ripen before frost unless you use a shorter-season variety, transplants, or season-extending covers.
What is the last spring frost date?+
It's the average date of the final killing frost in spring; planting frost-tender crops before it risks losing them. It's usually given as a date with a probability (e.g. the date after which there's only a 10% chance of frost). Use your local figure from a met service or extension office.
What is the sow-by date?+
The latest date you can sow and still have the crop mature before the first autumn frost — first frost date minus days to maturity. Sow after it and the crop is likely caught by frost before harvest. The tool calculates this date for you.
How do I extend my growing season?+
Start transplants indoors to gain weeks, choose short-season ('early') varieties, warm the soil with mulch or plastic, and protect with row covers, cloches, cold frames or polytunnels in spring and autumn. Each pushes the effective frost-free window wider.
Why add a safety margin to frost dates?+
Frost dates are long-term averages, so roughly half the years see frost later in spring or earlier in autumn than the average. Adding a 1–2 week buffer on each end protects tender crops from an unusually early or late frost.
Do all crops care about frost?+
No — frost-tender crops (tomato, maize, beans, cucurbits) are killed or damaged by frost, while frost-tolerant or hardy crops (wheat, peas, brassicas, onions) can survive light frost and even be sown before the last spring frost. Plan tender crops strictly inside the frost-free window.
What if my area has no frost?+
In subtropical and tropical zones with no killing frost, the frost-free window is effectively year-round, so a crop can be grown at almost any time. Plan instead around heat, the monsoon/rainy season, and market windows — pick the frost-free zone preset for this.
How does this relate to growing degree days?+
Days-to-maturity assumes typical warmth; growing degree days (GDD) measure the actual heat a crop accumulates. The frost window tells you if there's enough calendar time, while GDD tells you if there's enough warmth — use both for cool or marginal climates.
Are the climate-zone presets accurate for me?+
They're typical examples for broad zones, not your exact location. Always replace them with your own local last and first frost dates for a reliable result — frost timing varies sharply with altitude, valleys and proximity to water even within a region.