Benefits of a passive solar greenhouse are evident in cooler months: a warm place to get out of the cold and wind and still be able to garden. What is grown depends on the average night temperature of the greenhouse. Tender crops such as tomato, pepper, and eggplant set fruit best if the night temperature is above 55 degrees.

Many of us can't afford to heat a greenhouse at night. Fortunately , many crops are productive in a 'cool' greenhouse, including broccoli, Brussels sprouts, cabbage, cauliflower, chives, collards, kale, leeks, lettuce, mustard, peas, radishes, spinach, and Swiss chard.

The advantage of growing in a greenhouse is a constant supply of fresh greens and cherry tomatoes. Eating a salad of your own fresh lettuce during the middle of winter is a treat you must grow yourself to enjoy. Many of the tastiest varieties of lettuce and gourmet greens are too perishable to be seen in a grocery store.

Fall and winter lettuces, specially bred to cope with shorter days and cold, include Arctic King, North Pole, Winter Density, and Winter Marvel. Special greenhouse lettuces include Arkel and Magnet. These varieties are available from The Cook's Garden, Londonderry, Vermont 05148-0535. They also offer 13 varieties of loose leaf 'cutting lettuce' such as the intensely red Valeria which resprouts vigorously from a cut stem after harvest.

Another catalog, Vermont Bean Seed Co, Garden Lane, Fair Haven, Vermont 05743, has over 30 types of gourmet winter greens, including many quick growing Asian greens. These include ornamental and tasty little cabbages with names like Tatsoi, Tyfon, and Tsoi-Sim. This company also offers a catalog called Totally Tomatoes with 250 varieties of tomato.

Mesclun is a French term for a 'mixture' of young lettuces, greens, and herbs. All over Europe bags of mixed leaves are offered in open markets. Many greens used for mesclun have been in U.S. gardens since the 1600's. Examples include chicory, rocket, cress, chervil, and dandelion.

Mache is a European green, cultivated for its mild, nutty flavor. Unlike most lettuce, it can be harvested even after the plants bolt.

Arugola, also called rocket, is a popular salad green in Europe. It has a unique flavor that is not spicy or peppery. One of the easiest salad crops to grow, arugola adapts easily to indoor gardening. The leaves are harvested when 6 inches tall. Radiccio is an Italian heading chicory. Europeans value the bitter side of their taste more than we do. With the recent development of milder varieties, demand is growing for these gourmet salad plants. In the U.S. radiccio refers to the red varieties of perennial chicory. They resprout and are ready for another harvest 6 weeks later.

Seed greens several times a month for a constant supply and fertilize weekly. I use compost tea. Leaf lettuce needs plenty of water. Water for head lettuce is most critical as the inner head begins to swell. Even one day of dry soil can make the leaves touch and bitter tasting.

Harvest lettuce heads by cutting below the crown. Be sure to harvest before there is any elongation of the central crown of the plant. Once bolting begins, quality goes downhill. Mesclun and cutting lettuces are harvested when about six inches tall, with scissors, cutting the plants about one half inch above the ground. They then resprout and grown again.

Don't have a greenhouse? All of the 'cool' weather plants described above will also survive our local winter with the help of a cold frame or tunnel. I've also grown greens in my winter garden with the help of a floating row cover.