Gardeners in cooler climates are faced with the same dilemma almost every spring. The nights remain cool and the soil in the vegetable bed just refuses to warm up. Yes, they can sow some of the cool-season vegetables while the ground hasn’t yet warmed up (spinach, beets, radishes, peas, lettuce, etc.), but warm-season vegetables like things decidedly hotter: tomatoes, peppers, melons, sweet potatoes, etc. So, you wait, and wait, and wait.
Or you heat up the soil.
That’s where black plastic mulches come in. Sold in garden centers and online, they’re designed for a lot of things: to keep weeds down, to reduce evaporation, etc., but they’re also marvelous at raising the soil temperatures in spring.
The soil under black mulch will warm up quickly, in about 4 to 10 days, depending on local conditions. Then you simply punch holes through the mulch at the desired spacing and plant your tender vegetables in the holes. Dig! Drop! Done!
Often, although the soil is now warm enough, the night air temperatures are still too cool for your plants. Consider 55˚F (12˚C) to be a minimum, while 65˚C (18˚C) is much, much more to their liking.
So, add a step. Cover the plants with mini-greenhouse of some sort: a cloche, a transparent tunnel, a “tomato tipi” or just a sheet of transparent plastic raised on stakes. A mini-greenhouse combined with black mulch will keep plants nice and warm even on nights of light frost!
However, you’ll have to open or remove your mini-greenhouse on hot days and remove it entirely when summer settles in; otherwise the poor plants may cook in the heat!
What gardeners won’t do to get the earliest possible tomatoes and melons!