Greenhouse Vegetables

Speedier Veggies With Black Plastic Mulch

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.

Tomatoes planted out early using black plastic mulch. Photo: Nick Warren,

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!

Well, sometimes.

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.

A mini-greenhouse will keep your plants even warmer. Photo:

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!

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

1 comment on “Speedier Veggies With Black Plastic Mulch

  1. Goodness; that is too much work for vegetables that should grow like weeds. Well, if it is any consolation, we don’t grow peas, and can only grow cabbage, broccoli and cauliflower through winter.

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