What frost tolerance means
Frost tolerance describes how a plant responds to air temperatures at or below freezing. A hardy crop can take repeated light frost and often improves in flavour after one; a tender crop is damaged or killed by the first. The useful distinction for planning is not a single number but which of three groups a crop belongs to, because that decides when it can safely go out and how late it can stay.
Three working groups
Tolerates repeated light frost; can be sown early and left late.
- Kale
- Spinach
- Leeks
- Carrots
- Parsnips
Takes a light frost but not a hard freeze; plant near the frost-free date.
- Lettuce
- Beets
- Swiss chard
- Peas
- Potatoes (tops)
Damaged by any frost; wait until frost risk has passed.
- Tomatoes
- Peppers
- Beans
- Cucumbers
- Squash
Read the group, then the date
Decide a crop's group first; only then match it to your local frost dates. Hardy crops bracket the season; tender crops fill the warm middle.
Using the groups across a season
Hardy crops are the ones that make a short season feel longer. They can be sown while the soil is still cool and harvested after the first autumn frosts have ended the tender crops. The half-hardy group is the most weather-sensitive: it rewards waiting for a settled spell rather than the earliest possible date. Tender crops should not leave shelter until frost risk has genuinely passed for your area, which the public frost-date tools can help you judge.
A short season is not only about heat. Much of the extra yield in a cold region comes from the cold-tolerant crops at each end, not from forcing tender crops earlier.
Where to read next
Choosing crops is only useful if the soil can support them and the bed is used efficiently. See soil amendment and succession planting, and building raised beds for the structure underneath.
Reference: Agriculture and Agri-Food Canada, Royal Horticultural Society.