Cold Frames Extend The Growing Season

During the winter of 1990, East End residents were wondering if we were in the midst of a new Ice Age, and yet some of us were still harvesting vegetables from outside. During that winter I was called by a landscape architect who needed information on cold frames. The firm that he worked for was doing some very elaborate (and expensive) design work for a very wealthy client who was building a new home on Long Island’s North Shore.

I was very surprised that a project involving so much detail and dollars did not call for a greenhouse, but the clients were very adamant that a greenhouse was not necessary. All they wanted was a properly constructed and sited “colder” that might have some source of minimal heat in the dead of winter.

As a traditionalist, my first reaction was that a true colder (these days called a cold frame) was not heated and that what the client was actually seeking was a hotbed. But technicalities aside, the design was done, the frame sited and the client, I am told, remains ecstatic about this seemingly minor addition to a multimillion-dollar mini-estate. But why? Maybe fresh salad greens, beets, cabbage and carrots in January?

The answer is both simple and complex, and even if you have a small cottage with a tiny yard, there should be a cold frame in your future. The colder is one of many types of gardening structures that used to simply be referred to as “frames” or season extenders and now generally includes cold frames, hotbeds and a wide variety of smaller hybrids that fall into the category of grow tunnels. For now though, let’s limit our exploration to the colder.

Years ago virtually every large commercial growing operation used cold frames. They could be found alongside the greenhouses that used to be off Flying Point Road in Southampton, and out in Springs there was a nursery where the owner would propagate his famous rhododendrons in rows of cold frames.

You can still see the remnants of these frames at some older greenhouse operations, and one large retail garden center in lower Westchester County still grows most of its perennials (tens of thousands) in raised cold frames right in the retail area of the operation. Come spring they simply remove the sashes (glass coverings) and customers can pull their plants right from the frames. Should it get dangerously cold or icy, the sashes can easily be put back on top of the frame and the plants are protected from frost and freezes.

Commercial growers used frames to force potted bulbs such as tulips, daffodils and hyacinths and to overwinter perennials that were not field planted and for propagation on a year-round basis. For the home gardener, cold frames represent an opportunity to garden year-round without the need for a greenhouse, building permits, increased taxes or running water. If properly planned, it can be used for growing some vegetables on a 12-month basis instead of just during the summer, propagation of cuttings, germination of seeds that might otherwise be impossible to grow, for the growing of marginally tender plants and for hardening off numerous crops. I’ve even seen frames that are used to start annuals and vegetables early in the season and as the weather gets more hospitable the sashes are removed so the frame becomes a sunken flower bed or vegetable garden.

An uncomplicated colder is simply a rectangular boxlike affair that is covered with glass sashes (though other materials are mentioned later in this column) that is sited to take advantage of maximum solar gain in winter. This “box,” or frame, is generally 3 to 5 feet wide and can vary in length depending of the needs of the gardener. Sizes for homemade frames should be standard lengths and widths to take full advantage of standard wood and sash dimensions. The structure is built with the sash slanting, usually facing south, with the back 9 to 12 inches higher than the front.

For the conservation of heat gained during sunny winter days, the north wall of the frame can be butted against another structure like a house or garage foundation. If the unit is to be a stand-alone, the north wall can be bermed or insulated with rigid foam or insulating foil-backed bubble wrap for added heat retention.

To add versatility to a colder, a source of heat can be added to the bottom of the frame, and if the frame is large enough it can be compartmentalized so that only a portion of the frame is heated while the neighboring compartment is permitted to both heat and cool more naturally. Even in an unheated frame the temperature differences between the inside and outside temperatures, both night and day, are dramatic.

For several years I kept records on a stand-alone colder that was bermed on all four sides and had some foam insulation added to three sides. Even on a cold, windy, clear day when the outside temperature hovered in the single digits, in Shinnecock Hills the temp in the frame never went below freezing. For the whole winter, the soil and plants in the frame only froze for short periods of time and it was never enough to damage the lettuce, spinach, carrots and beets that were harvested right through January.

Construction materials can be used or new and the sources for sash materials are almost limitless, especially if there are any house renovations going on nearby. A local junkyard can also be a gold mine for a project like this. You can probably build a frame of 9 to 12 feet in length for under $600 (and some skill and ingenuity) and you should expect it to last for 10 years or longer.

For slightly less money (and less work if you’re not handy with a ruler and saw) you can buy one of the newer prefab cold frames that are set above ground and are made of aluminum and plastic or fiberglass glazing materials. An example would be the Juwel BioStar which sells for about $400 and is 5 feet long, 32 inches wide and 16 inches at the front and 20 inches at the back.

These types do not provide nearly as much protection from the dead-of-winter cold and are marginally useful from December through late February as most sit above the ground. They are very susceptible to wind damage and can be a bit flimsy, but they can be easily placed directly in the garden where vegetables and flowers can be started many weeks earlier than if the plants were directly sown or store-bought. Just seed or plant in situ, and when the weather is favorable, simply lift and remove the frame.

Low tunnels are another variation on the theme. These are low plastic tunnels supported by wire frames or bent metal tubing with clear to opaque plastic film covers. They’re not as versatile as a traditional cold frame but can be excellent season extenders (spring and fall) for root crops, greens and even strawberries.

Next week, how to build your cold frame and some links to free plans. Keep growing.

It’s important to keep the leaves off your lawn as they fall from the trees, but mulching them (with a mulching mower or mulching blades) is even better. Remember that oak leaves don’t compost easily, but when mixed with grass clippings and maple leaves they will decompose faster.

Still time to test your lawn and garden soils for pH. The newer types of lime can be applied with a spreader well into November and are fast-acting. Older types of lime can take up to six months to show results.

Do you really need to feed your trees? Fruit trees, yes. Ornamental trees, usually not especially if they are mulched with compost. Never feed hemlocks that have woolly adelgid issues; feeding them just makes the problem worse. When in doubt, remember that no one goes into the woods to feed the forest. But in the landscape, there may be some trees and shrubs that benefit from feeding.

I don’t care how supple and soft your garden hoses are. They are much easier to drain, coil and store on a warm, sunny November day than a cold day in December.

Need parts for hose repairs, mower blades and other repair items for your tools and equipment? Buy the parts you need now and don’t wait until the spring. You know — supply chain issues.

And speaking of supply chain issues, plant material, especially trees and shrubs, may still be in short supply next spring. Speak with your garden center now and place early orders. Even mail-order nurseries are taking early orders this year, and if you place orders now you’ll get at the front of the line come shipping time. Right now the biggest issue seems to be shipping boxes.

The original long-range weather forecasts for this winter were cold and wet and possibly the coldest and wettest in four to eight years. Now, not so sure. After all, it’s weather.