Cold frames are a great way to extend Maine’s short growing season. Seedlings can be started earlier in the spring, and late-season crops extended well into the fall – or even early winter. Cold frames give delicate plants both protection and the benefits of outdoor sunshine. Plenty of designs are online to suit different needs, budgets, tastes and carpentry skills, but these basics apply to all cold frames:

Design your cold frame with an adjustable opening, so you can modify it according to the temperature and sunlight. Sun is good, but too much sun can overheat and kill the seedlings.

Make cold frames from scrap lumber scavenged, recycled or found around the house. Old window sashes, for example, can be turned into lids to hinge on to the cold frame. Or buy the materials – they aren’t costly.

To get the sun’s maximum benefits, situate the cold frame so its “low side” faces south.

Cover the windows with plexiglass or heavy plastic sheeting.

To retain the day’s warmth, line the cold frame with rigid insulation or place jugs of water inside it. They’ll warm up during the day and moderate the temperature at night.

Layer rich soil capable of starting seedlings inside the cold frame or leave the ground bare and set seedling flats or pots on it.

To keep the lumber from rotting, lay bricks beneath the cold frame.