How to Protect Your Crops From Cold Weather

25 September 2009, written by Barbara Pleasant

If you garden where winter temperatures often drop below 10°F (-12°C), setting up a winter tunnel in autumn can bring tremendous payoffs. You can use the protection of a plastic-covered tunnel to extend the harvest of late-season leafy greens or to improve the winter survival of marginally hardy plants. Lastly, a tunnel or frame makes a fine home for late sowings of super-hardy spinach and mache. The little seedlings will sit patiently through the coldest months and explode with new growth first thing in spring.

Making Autumn Last Longer

Most of the leafy greens and cabbage family crops used for late season planting benefit from a touch of frost, because chilly temperatures enhance their flavours and textures. But a hard freeze – defined as temperatures below 26°F (-3°C) for more than 6 hours – often causes serious damage, especially when the cold temperatures are accompanied by biting winds.

In my garden, I dig and move young plants as needed in September, to bring them together into a collection I can cover with a plastic tunnel held aloft with hoops. The cover won’t actually go on for several weeks, but moving plants about while the weather is still mild helps them become established in their new locations. Leafy greens like rocket and lettuce thrive beneath a winter tunnel, as do most Asian greens. I’ve found that a tunnel also keeps my kale and collards in prettier picking condition, so I usually locate the tunnel wherever I have a few healthy kale or collard plants already in the ground.

Enhancing Winter Hardiness

In my garden, winter temperatures often fall to 5°F (-15°C), which will kill unprotected parsley and coriander, as well as half-hardy greens like rocket and mizuna. The story changes when these crops are covered with a tunnel or glass-topped frame that insulates them from ice, snow and temperature extremes. To further ensure the plants’ survival, I throw old blankets over the tunnel or frame when very cold temperatures are predicted. Plants that are pulled through winter under cover put out a fast flush of growth first thing in spring, and then quickly bolt and bloom. This is a good thing! Bees love the flowers, and select plants can be allowed to produce a nice crop of fresh seed – some to gather and store, and some to "plant" by laying seed-bearing branches atop a prepared planting bed.

Alt text — Mache, also known as lamb's lettuce or corn salad

Pre-Planting for Spring

By late winter I’m hungry for fresh leafy greens, so the last winter tunnel or frame I set up is dedicated to spinach and mache (also known as lamb's lettuce or corn salad) – surely the hardiest of leafy greens. Seeds planted in the frame barely have time to germinate before their growth slows to a crawl due to the short, dim days of winter. The big drama comes in March, when the protected babies quickly grow into robust plants.

My current collection of undercover gear includes several reconditioned window frames, a cold frame topped with a recycled shower door, support hoops made from wire and plastic pipe, and several sheets of horticultural fleece and clear plastic. Please add to this list and offer your tips for taking your garden under cover as the growing season nears its end.

By Barbara Pleasant