Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern & Central Midwest
March, 2012
Regional Report

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This lovely brick cold frame is awaiting its new crop.

Jump Start Spring with a Cold Frame

I don't know about you, but I'm really antsy to get something started for the garden season. I actually took a peek in my cold frame recently and my spinach is doing splendidly. It won't take long for the leaves to take off and I'll be enjoying fresh salad from my own garden.

Pick the Best Plants
Extending the season is not hard, especially if you are willing to do a little construction to build a cold frame. This lets you actually add four to six weeks to the front end and back end of the growing season. The cold frame concentrates the weak spring sun and makes the plants toasty and warm, especially if you orient it to face south. The best candidates for spring growing are cool season leafy plants such as lettuce, spinach, Swiss chard, and other greens. They are very cold tolerant and don't need much heat at night.

Harden Off Seedlings
Once summer begins to heat up, the cold frame can be used to help harden off seedlings that were started indoors. They are protected from wind and simply need to be shaded for the first few days out.

Recycle Materials to Build a Frame
Although there are plenty of elaborate structures and kits available commercially, it's possible to build a very simple box and use a window sash to cover it. You can use brick, cement block, wood, or even straw bales. This is a great time to scavenge for discarded materials to recycle. You can also build a tunnel of plastic and PVC, but it's critical that it be strong enough to hold up under a snow load if you leave it out over winter.

Protect Plants on Cold Nights
The better sealed the box is, the better your plants will be protected from wind and cold. Blankets or bags of leaves put over the top at night will help the cold frame store heat. A great way to help add warmth at night is to put plastic water bottles painted black and filled with water around the edges of the frame. When the lid is closed for the night, the bottles of water can actually raise the inside temperature by twelve to fifteen degrees.

Make Sure to Open on Sunny Days
You have to make sure to open the top of the cold frame during sunny days or your plants will cook. There are automatic openers that can do this for you if you can't be home. Try not to let the temperature rise above 80 degrees inside. Invest in an inexpensive thermometer to monitor temperatures inside the cold frame. For the best southern sun exposure, make the south side of the box lower than the north side and try to orient the box east to west. You can even paint the inside white to reflect sunlight back onto plants.

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