Many avid gardeners find themselves in a predicament when winter arrives – you have too many tender plants (that you’d rather not compost) and not enough storage space. Since most homes have a limited number of available windowsills and few homeowners have a greenhouse (or can afford to heat one), one solution is to build a cold frame for your plants using bales of straw.

Straw bale cold frame

Protect your plants with a simple straw bale cold frame.

Photo Credit: John Buettner

Straw bale cold frame with leaves

A leaf layer over top of the plants creates a naturally insulated area.

Photo Credit: John Buettner

Straw bales are cheap and easy to lift into place. (As an added bonus, you’ll have plenty of mulch come next spring!) The straw cold frame is best suited to shelter newly acquired plants and rooted cuttings that may not handle freezing weather. They can also be used to protect container plants or any tender growers you may have dug up and stuck in temporary pots for overwintering. Be warned, however: This structure won’t work for tropicals that can’t handle even a light frost.

Making a straw bale cold frame is easy. Begin by scoping out the best location – preferably an open, level spot. It’s important that you place your straw bale frame carefully in the right location, because bales act like giant sponges – once they endure a rainy day or two, they’ll soak up enough water and become too heavy to lift or rearrange easily. Build a cold frame in a sunny location for leafy plants, and build one in a shady location for anything that goes dormant during winter.

Arrange your straw bales in a rectangular shape no more than one-bale-wide to avoid cold pockets in the center of the structure. The length of the cold frame can be as long as necessary to accommodate your plants, so you can use as many bales as needed there. The long box shape creates a microclimate of warm air. If the rectangle is too wide, the pocket of warmth won’t extend all the way across the cold frame. If you need more space, just build more cold frames. Secure the straw bales by pounding small wooden or metal stakes through the bales and into the ground.

The roof of the cold frame depends on the climate. Gardening in Raleigh, NC, I rarely need to cover the top for the first month of colder weather. For mild protection (in temperate areas), a simple protective covering can be made of dry leaves or loose straw mulched directly over the plants. The higher the leaves are mounded (to the tops of the bales), the more insulated the plants are from the cold temperatures.

Some temperature regulation may be required for your cold-framed plants, especially during warm spells through winter. Carefully uncover the leafy plants, but leave any dormant plants covered. When the cooler temperatures return, remember to reapply the protective cover.

For additional protection in colder climates, you can cover your cold frame with plastic sheeting (found at your local hardware store or garden center), which will turn your cold frame into a “mini-greenhouse.” If you choose to use the plastic roof, pay close attention to the cold frame on sunny days – a plastic-covered cold frame can quickly get too hot for most plants.

When cool temperatures have given way to warmer spring days, disassemble the cold frame. By using the straw bales as mulch, there’s no cleanup and no storage of this effective, easy and affordable overwintering structure.