Gardening under wraps

Few serious gardeners can resist the idea of harvesting crops in the dead of winter.

Several years ago, Joe Thomasson's neighbor routinely spied on him each time Mr. Thomasson tramped through the snow to harvest vegetables from under the conical shapes in his backyard.

One day the neighbor shouted out his back door, as Thomasson was harvesting spinach, "It's a good thing we know you, 'cause folks who don't would think you're crazy." Thomasson gave the neighbor a few Plant Houses he co-invented.

Now the neighbors wave at each other as each braves the Kansas winter to harvest their produce. They exchange a gardener's brand of fish tale - Thomasson boasts harvesting salad greens for Thanksgiving dinners, potatoes on Christmas Day, and spinach in mid-February. His neighbor picks broccoli in early January.

Every year at least one new season-extender product hits the market.

Yearning to grow in snow inspired Thomasson to invent his system along with John Van Dyke. (Mr. Van Dyke had already dabbled in methods to extend the growing season, including burying heating cables in his Kansas soil.)

Plant Houses are portable 2-foot-tall cones, assembled from three curved, opaque, laminated plastic walls that hold four gallons of water between them. They are a sturdier version of Wall O' Waters, pliable, soft plastic cones that appeared on the market more than a decade ago. All of these water-filled cones are essentially plant igloos, insulating interior surfaces and protecting plants to 20 degrees F.

Such devices expand planting and harvest times by about a month. Cool-weather crops such as beets, lettuce, spinach, and cruciferous vegetables such as radish, turnip, broccoli and cabbage can be planted in February or early March, and be harvested as late as December. Warm-weather crops like tomatoes, traditionally planted in late May or early June, can go in the ground as early as April.

*Plant Houses have been available only a year or two, although water walls are a concept that dates to 19th-century Germany, according to Thomasson, a Hayes University paleobotanist. His product is sold through Ideal Products in Wichita, Kan., for $12.99 (800-249-9725).

*Wall O' Waters has been around considerably longer and is found in most gardening catalogs and even in garden centers, priced at $10 per unit.

This year's catalogs are seeing several variations on another 19th-century invention: cloches. Traditional cloches were bell-shaped glass domes that French market gardeners placed over spring and fall crops to stretch their growing seasons.

American season-extenders have used the most affordable form of this principle: plastic milk jugs with the bottoms cut out. But this latter cloche variety protects crops by only a few degrees.

*Hotkaps - waxed-paper tents - are another long-marketed American variation of cloches. These protect young seedlings in early spring, but only once soil has heated to about 50 degrees F. because they neither harness heat nor insulate. Available at garden shops and through mail-order catalogs, they range from $9.95 to $15.50, depending on size.

*A glass cloche, insulating to 22 degrees F., is being marketed through Gardeners Eden (800-822-9600), and Lee Valley Tools (www.leevalley.com) for $12.95 to $22.

*Plastic variations, small and large Solar Bells, protecting to 26 degrees F., sell for $5 to $20 (Kinsman Company, 800-733-4146).

*Solar Umbrellas, offering clear vinyl protection to 28 degrees F. and easy use, are selling for $15 at Lee Valley and Garden City Seeds (406-961-4837).

*Agro blankets - lightweight spun bonded polypropylene or nonwoven polyester, are cost-effective. Available in mail-order catalogs in rolls of varying size at prices from $7.95 to $62.80.