First Frost Date Calculator: Autumn Planting Deadlines
Autumn crops are planted in the heat of summer but mature as days shorten and cool. To harvest before the first frost, count back from it by the days to maturity, plus a couple of weeks because growth slows in autumn.
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What this calculator does
Choose your zone or enter your local average first frost, and your crop's days to maturity. The calculator gives the sow-by date and a table for common autumn crops.
How to use the first frost date calculator
- Choose zone estimate or enter your local average first frost date.
- Add a safety margin if early frosts are common.
- Enter days to maturity from the seed packet.
- Keep 14 days for the autumn slow-down.
- Sow on or before the date shown.
How the calculation works
planning frost = average first frost − safety margin sow by = planning frost − (days to maturity + autumn factor)
Hardy crops such as kale, spinach and carrots survive light frosts, so they can be harvested after the date shown.
Worked example
In zone 6 the average first frost is around 17–31 October (midpoint 24 October). A 60-day crop with the 14-day autumn factor should be sown by about 11 August.
Assumptions and limitations
- Frost-hardy crops can stand later; tender ones such as beans stop at the first frost.
- Row covers and cold frames extend the season by weeks.
- Use local frost data where available.
Frequently asked questions
When should I plant a fall garden?
Count back from your first frost by the crop's days to maturity plus about two weeks.
What is the fall factor?
Extra days added because shorter, cooler days slow growth in autumn.
Which vegetables can survive frost?
Kale, cabbage, spinach, carrots, leeks and Brussels sprouts tolerate frost; many taste sweeter after it.
When is the first frost in zone 6?
Typically in the second half of October, but it varies by site.