1. To over-winter plants you want to grow during the winter months
that are too sensitive to the cold.

2. To start seeds earlier in the season by building a closure over the
plants to keep moisture in the soil and keep plants warm enough
during that early season.

4. To start plants in a greenhouse and harden them off in the cold-frame.

Many kinds of plants may grow well in a cold-frame, according to Johnson.
“Herbs work quite well,” she says. “Lettuces, cucumbers and squash may be planted in cold-frames in early spring – as early as March. You can, basically, extend your growing season by about two months using a cold-frame.”

Cold-frames differ from a greenhouse in that they are usually smaller and you don’t walk into them, according to Pawl Hollis, owner of Rail City Garden in Sparks.
“Cold-frames are generally buried into the ground,” says Hollis. “They are not heated. They rely on the biomass of the soil to keep warm. They collect solar heat during the day and distribute that heat at night.”

Some vegetables actually prefer the cold weather, says Hollis.
“You can start seedlings early and go into the winter months,” he says, “like lettuce, radishes, herbs, spinach, Swiss chard, kale, carrots – they can all do quite nicely. They like the cold weather. They just can’t freeze.”

“Late season or cool-season crops do well in a cold-frame,” adds Bill Carlos, horticulturist for the Wilbur D. May Arboretum and Botanical Garden, Washoe County Regional Parks and Open Space. Start leafy lettuce and other cool-season crops such as broccoli in October, and time them to mature in early to mid-December for fresh, homegrown vegetables during the holidays.

Soil
Johnson and Hollis agree that the best soil to use in a cold-frame is organic.

“You want to have a lot of micro-organisms,” says Hollis. “You may use packaged potting soil. It can have sand, peat moss and bark. You need it to be porous for aeration, not heavy. You want it to retain water but have good drainage. It should have high organic material.”

“Organic soil helps retain the heat better,” adds Johnson. “You can also pile mulch around the base area of the plants in the cold-frame. The mulch is always breaking down, making its own warmth.”

Fertilizer
“I’m a big advocate of organic fertilizers,” says Hollis. “You want to keep a pH balance of about 6.5. Add the right amount of kelp meal, alfalfa meal or fish meal to keep it in balance.”

Fertilizing when it’s already too cold, however, doesn’t help the plants, says Johnson.
“When the soil is 60 degrees or below, the soil won’t take up the fertilizer,” she says. “If you’re going to plant in the spring, fertilize in October, before it’s too cold. Then, place your cold-frame closure over it. The fertilizer will get taken up for the spring planting.”

Air

Some gardeners underestimate just how warm it can get inside a cold-frame and how important it is to open it up during the heat of the day to let the plants breathe, says Hollis.

“If we have a real calm clear day, it can get real hot – about 100 degrees,” he warns. “Plants need to dry out and cool off. Some people try to get them too warm. It’s more important that the roots stay warm than the tops of the plants. Keep the root zone warm and the top of the plant cool. You’ll have less disease that way.”

Planting time

The best time to plant when using a cold-frame can be determined by reading the seed packet, according to Johnson. “Back it up by one month,” she says.

Water

As for how often to water, “Watering depth and ratio should not change when using a cold-frame,” says Johnson. “The only thing you change is how often you water,” she says. “Give your plants the same amount of water each time you water. Saturate the roots.”
“Use a good organic soil, utilize a compost pile and cultivate the soil with new organic material,” says Hollis.
Whether you buy or build your own cold-frame, follow these tips and add two months to your growing year!

Susan Botich is a Minden-based
freelance writer.