Day 29: Extending the Season in Your Vegetable Garden, Part 2

By carefully choosing which crops and varieties you grow in your vegetable garden, it’s possible to extend the growing season several weeks in the North. But frost is frost, and eventually all but kale and parsnips will fall to its power. For determined season extenders, the next step is to add layers of warmth to the garden through covers, hoop houses and cold frames.

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This high tunnel at a school provides greens early and late in the season.

In her article called “Cheat the Season,” in the September/October 2012 issue of Northern Gardener, Colleen Vanderlinden offered 10 ideas for extending the growing season. She noted that Maine-based author Eliot Coleman reports that for every layer of cover you add to a vegetable garden, you gain one zone in warmth. So, adding one layer of cover moves your garden from Minneapolis to Des Moines; add a second layer of cover and you’re in St. Louis.

The simplest layer of cover is to add something to protect one or a few plants from early frost — a sheet, a fancy cloche, a plastic milk jug with the bottom cut out, a row cover. But many season extenders want to be able to harvest into November or even December, and for that you need something like a greenhouse. The difference between a hoop house, low tunnel, high tunnel and a full-on greenhouse isn’t strictly a matter of semantics; generally a greenhouse is a more permanent structure whereas a hoop house or low or high tunnel is temporary.

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A gardener harvests in relative comfort inside a high tunnel.

What most home vegetable gardeners are seeking is a low tunnel or  hoop house, which can be made out of PVC pipe or electrical conduits that are bent around a raised bed to make a frame. The frame is then covered with plastic of some kind (Colleen recommends simple painting drop clothes for small low tunnels). You can find several videos on youtube on how to build a hoop house on the cheap. Most of these are made by home gardeners and offer creative ideas on how to construct a simple tunnell. In making your hoop house, it’s important that you be able to move the plastic covering off or on the frame easily. Our weather is erratic –  even more than usual in recent years — and fall days can go from 20 degrees to 60 in a snap and your garden could get very warm quickly. Another consideration is wind. I’ve tried several home-made coverings on my garden and battening them down against the gale-force winds in my area has been a challenge.

A low tunnel is great for giving plants the extra days or weeks they need to finish growing. Also, if you start some spinach, lettuce or other greens in late August, you should be able to leave them in a low tunnel or hoop house and harvest well into the fall.

How do you extend your gardening season?

Mary Lahr Schier

Tomorrow: Preserving the Harvest.