A paleobotanist at Ft. Hays State University in Hays, Kan., Thomasson co-invented the Plant House with fellow gardener John Van Dyke, who had spent years tinkering with ways to cultivate vegetables during the winter--everything from heating soil with electric cables to hydroponics.

Their Plant House is an assemblage of three curved, laminated plastic walls that hold four gallons of water among them. You pour the water that insulates interior soil surfaces through a hole at the top of each wall and then dovetail the walls to form a perfect 2-foot-high cone. A vented plastic lid is the roof to the opaque cone, so interior plants get the sun they need while being protected from snow, hail and any other harmful elements, including critters.

Generally, water-insulated devices heat their interior surfaces about 20 degrees warmer than outdoor temperatures. Using them extends traditional growing seasons by six to eight weeks in fall and in late winter. Cool weather crops--spinach, lettuce, broccoli, radishes and beets, for example--planted in their interiors can be harvested as late as November or December and planted in late February or early March. Warm-weather crops, such as tomatoes and peppers, can be planted in them in early April.