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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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.
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.
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.
Count back from your first frost by the crop's days to maturity plus about two weeks.
Extra days added because shorter, cooler days slow growth in autumn.
Kale, cabbage, spinach, carrots, leeks and Brussels sprouts tolerate frost; many taste sweeter after it.
Typically in the second half of October, but it varies by site.