Frost Tolerance in Plants

When autumn is approaching, so is the cooler weather. This can have several different effects on your garden, including:

  • End-of-life for your most tender hot crops that cannot withstand even a light frost
  • Survival risk to your cool crops that can withstand a light frost but not a hard frost
  • Slower growth rates for all vegetables

This does not mean an end to your gardening. Rather, you just need to make sure you know your frost dates and you choose the right vegetables for your garden.

The key is to know your region’s frost dates. There are two dates that you need to worry about – the first frost date and the hard frost date. Here are a couple of useful sites to determine your first frost date:

Note that even these sites can have 1-2 week differences, which is reflective of the weather variability in autumn. If you have hot crops in your garden, choose the earliest date and plan around that. If you have cool crops that can withstand some freezing, then you have some latitude and can plan around the later date.

The hard frost date is not typically published so you should keep your own records. In most of southern Ontario, the first hard frost date is in early November.

With this information in hand, you’ll know which vegetables can stay in the ground through much of autumn. A few of the vegetables that can withstand a hard frost include broccoli, cabbage, fava beans, kale, leeks, mache (corn salad), mustards (including arugula), radish, spinach, and turnips. These vegetables can be started late in the season and can be grown through much of autumn. Further information on choosing the ideal vegetables for a fall planting can be found in this blog post.