Cold Frames: A Warm Spot for New Plants

You can introduce your seedlings to the cold, cruel world in a warmer, gentler way by using a cold frame.

A cold frame is simply a structure or frame, usually covered with plastic or glass that can be closed at night to keep warmth in, but opened in the day to allow good ventilation. It provides a location with lots of light where your plants can begin to adapt to outside temperatures in a protected area.

Seedlings started indoors need light to keep them from getting too tall. Once the seeds have germinated in your home, they need as much light as possible for best development. How you start them depends on your needs.

It you are planning a large garden, with long row of vegetables; you might want to start your seeds in seed flats. After about three weeks, move the stronger plants into peat pots and then to the cold frame for eventual planting in the ground.

If you are planting just a few plants of several varieties, you can plant seeds directly into peat pots from the beginning. After germination, which can take form three to 19 days, the plants need as much light as possible. Most little plants just are not cold tolerant and they won't be ready to be planted outdoors unprotected until approximately mid to late May. In order to help them adapt more easily, a cold frame is a perfect interim spot.

The cold frame's outdoor location also gives plants ample light that will help them become stronger, sturdier plants with thicker stems, rather than long and gangly plants. While tall and thin may be fine in humans, in plants, it is not as healthy.

Let's say you've started your seed indoors around late March. After three weeks, you're ready to move them to the cold frame. In choosing a cold frame, you have many options. You can either purchase a ready-made cold frame or build one yourself.

Remember, you will need to store the frame the rest of the year, so consider that when choosing the kind you want.

Small cold frames typically have a moveable lid to allow opening during the day and closing at night. Larger structures can have moveable sides to enable opening. They must be opened during the day to prevent overheating the little seedlings in the sun - after all, we don't want to cook our vegetables until they're ready for harvest. Closing them at night prevents too much temperature fluctuation.

I've seen people use their basement window well with a simply made lid to cover it at night. You can build a cold frame yourself with wood strips or narrow boards hammered together in a frame-like structure and covered with plastic. I have even used a stack of cement blocks with a portable top that I dissemble when not in use. If you want a more elaborate structure, you can build a base with a lid that props up. The "best" method is what is easiest for you. Just make certain you have a structure that allows ample light and can maintain warmth while permitting ventilation. Even on a cold spring day, when the temperature might only get to 32 degrees, a sealed cold frame could easily reach 70 degrees in the sun. Thus, you must vent and cool your plants as you let them grow.

Most importantly, this interim step will provide ample light that your plants so desperately need to keep them short and stout. Indoor light is just not as effective, even using a special "grow" lamp. Also, remember what happens to your skin in the middle of May if you're exposed to sun all day after a winter of being indoors - you get sunburned. Plant leaves won't exactly burn the way some people's skin can, but the intensity of the sun can cause damage.

Holding your plants in a cold frame before placing them in your garden or landscape will get them off to an earlier and healthier start.