Cool Season Planting

When it comes to planting out vegetables May is usually the first month that comes to mind. For most areas in Idaho the last frost date falls some where in May and that is when gardens are started. But that doesn't have to be the only time. There are a group of vegetables know as cool season vegetables. What that means is they thrive in the cooler weather of spring. They tend to bolt or stop growing when temperatures reach above 70 F for a prolonged amount of time. Some cool season plants prefer to be started in the spring and continue to grow and mature during the hotter days of summer. They need the cool spring time to grow a healthy root system. Having a healthy, strong root system helps them to recover better from pest damage or other environmental dangers later in the season.

This group of vegetables will handle a light frost in the spring and include asparagus, broccoli, brussel sprouts, cabbage, collard, garlic, horseradish, kale, kohirabi, leek, onion, pea, radish, rhubarb, shallot, spinach, turnip, beets, carrots, cauliflower, celery, chard, chinese cabbage, lettuce, parsnip, potato and swiss chard.

While these plants will handle cooler weather just fine they do their best growing when the soil is between 50 to 65 degrees. Most of Idaho does not reach that soil temperature until April or May at the earliest. Using a cloche, cold frame, or low tunnel with a floating row cover over the plants can help warm the soil in the early spring. This would allow sooner growing of cool season plants and protect them at night if the temperatures do dip below freezing. When using a cover on cool season plants it is important to monitor the temperature inside the cover on sunny days. Plants can quickly heat up and become to hot under covers. Opening the cover on sunny days helps to prevent to warm of temperatures.

My personal favorite cover to use on cool season vegetables is a floating row cover. The ones I use allow the transmission of water and 85% of light. They also add a 4 degree difference. That means they will protect plants down to 28 F. They can be left on when there is a cold snap and if I forget to take them off on a sunny day the plants will not over heat.