Cool crops are vegetables that can withstand temperatures below 10oC, and in many cases, they cannot withstand hot summer temperatures.
Cool crops are an important part of gardening in Canada as they allow us to grow food in the spring and autumn while saving the summer months for the hot crops. The result is that we can get three sets of harvests from each space of our garden. To achieve this, timing is key!
Let’s first look at the cool crops themselves. There are two broad categories of cool crops:
- Those that can also withstand the summer heat – These are usually root and stem crops such as beets, carrots, chard, fennel, kale, kohlrabi, leeks, onions, potatoes, and turnips.
- Those that should avoid sustained temperatures above 25oC for risk of bolting (flowering) – These are primarily leafy crops, including arugula, bok choy/pak choi, broccoli, Brussels sprouts, cabbage, cauliflower, cilantro, collards, fava beans, lettuce, mache, mustard greens, peas, radish, and spinach.
Cool crops that can withstand summer heat can be planted whenever you’re ready. Ideally, they can be started as early as possible (even early April for some) as they can withstand light frost. In general, it’s best to plant them sooner in order to harvest them sooner and free up your garden for the next crop. You don’t need to wait until late May to start planting in your garden!
Cool crops that can’t withstand the summer heat must be planted quickly. More specifically, you’ll need to plant them so that they’ll fully mature and be out of your garden before the hot summer days of July and August. If these vegetables are exposed to prolonged heat, they may get bitter. For exactly when to plant, find the days-to-maturity from the seed packet, and add ten days to that number if it’s still quite cold outside. Then, subtract that from July 1 to get the deadline for planting this type of cool crop outside. For very slow-growing cool crops such as broccoli, cauliflower, and Brussels sprouts, you’ll need to start these plants indoors in March to harvest them by July 1.
As a quick point to highlight, most cool crops can be planted as soon as you can work the soil or, at a minimum, as soon as the risk of a sustained period of frost or heavy snow has passed. Cool crops can tolerate a little bit of snow or a light frost.
If you cut it close and may end up with cool crops planted in your garden during periods of heat, make sure they’re placed where they’ll be shaded from the late-day heat.
In summary, cool crops are some of the best vegetables for Canadian gardeners. They enable us to start growing sooner each spring and later each fall. The result is that we can get three harvests per year in all areas, leading to more productive gardens and more food to enjoy!