Turn Raised Beds Into A Mini-Greenhouse

As a raised-bed gardener living in an area with cool or even downright frigid winters, you easily can extend your garden harvest into the cold weather months by adding hoop covers to the beds. The resulting hoop house—an arched framework over the bed covered with clear plastic and secured in place—functions as a mini-greenhouse.

Here are examples of several ways to accomplish this, most of which are fairly simple and inexpensive.

A number of garden supply companies offer a product consisting of a pair of metal wires joined together with cross braces called Super Hoops that can serve as a framework for hoop covers. Or, you can use flexible half-inch polyvinyl chloride (PVC) pipe to build your own framework.

For a do-it-yourself PVC hoop house, the lengths of pipe that will become the hoops should be at least double the width of your raised bed. Place them at least every 2 feet along the length of the bed. You can simply push the pipe ends into the soil, or alternatively, sink a dowel or piece of rebar into the soil and fit your pipe onto it.

See example photos of the latter, and additional methods, in this blog post.

An optional PVC or wooden ridgepole across the top, secured to each pipe, will add additional structure to protect your hoop house in high winds or heavy snow.

Cover the frame with 4- to 6-millimeter clear plastic. A clever way to secure the plastic to the poles is to use short lengths of discarded garden hose, split lengthwise and fitted over the plastic and poles. Hold down the plastic at the bottom of the house with a board or other heavy objects, such as bricks along the edge of the frame, or use spring clamps to fasten the plastic to the sides of the bed for easy access to tend your winter plants.

Best plants for winter hoop gardens

Cool-weather greens such as lettuce and spinach are best choices for winter hoop gardens. Additionally, root vegetables, such as carrot, turnip and parsnip varieties with short planting-to-maturity times, can provide winter meals.

Harvest plants such as kale, broccoli and cabbage into the winter by giving them a three- to five-week head start in the fall before first frost. You can do the same with greens such as bok choy, a Chinese cabbage; mizuna, also known as Japanese mustard greens; and mache, a nutty-flavored European green also called corn salad.

Note that as long as the soil in the raised bed is sufficiently moist before the bed is covered, there is little reason to water it during the winter months as long as the cover is kept secured. If you choose to open it during warmer periods, you may need to add moisture.