Caring for greenhouse plants; a greenhouse calendar. A “cool” greenhouse, kept at 45°F to 50°F at night, will support a wide variety of vegetables and ornamental plants; with a heated propagator, you can germinate most annual and vegetable seeds. Many more varieties will grow in a “warm” greenhouse, 60°F to 70°F at night, but it’s expensive to heat. In an intermediate greenhouse, kept at 50°F to 55°F at night, you can experiment with subtropical and the hardier tropical plants.
Extend the range of your greenhouse by taking advantage of, or creating, microclimates within it. Use a portable heater in conjunction with a humidifier to raise the temperature in one part of the greenhouse. In hot weather, keep the temperature relatively low by ventilating and shading and by damping down walkways and the gravel beneath benches. Caring for greenhouse plants
Don’t use ordinary garden soil. Buy ready-made potting and seeding mixtures. Or make your own soil by mixing equal parts of loam, builder’s sand, and humus or peat moss; sterilize the dampened mix by heating it in the oven at 180°F for 45 minutes.
Check the soil in the greenhouse every morning; water plants as needed. To increase humidity on hot, dry summer days, damp down two or three times a day or spray all the plants-except those with velvety or hairy leaves-with water. Feed plants in need of a little stimulus every 2 to 3 weeks during the growing season with a complete liquid fertilizer. Controlling pests and diseases Keep the greenhouse and the area around it clean. Don’t use it to store garden tools, which can harbor pests.
Buy plants from reputable nurseries. Inspect new plants for pests and signs of disease. Recheck regularly and remove dead flowers and decaying leaves. Apply pesticides as needed. Isolate unhealthy plants until they improve; throwaway badly diseased or infested ones. A greenhouse calendar January: On mild, calm, sunny days, ventilate discreetly. Water sparingly to avoid excessively dry or wet soil. February: Sow seeds of Cape primroses, coleuses, snapdragons, petunias, begonias (minimum temperature must be 55°F to 60°F). Toward the end of the month, sow tomatoes for planting out in April in regions where weather permits. March: Increase ventilation and start shading plants that maybe injured by full sun. Sow the seeds of annuals and of halfhardy and tender perennials for summer flower beds. Start growth of achimenes, amaryllis, and tuberous bego-nias. Transplant seedlings to pots or flats. Prune climbing plants that bloom on shoots of the current season. April: Increase ventilation and shading. Water freely. Sow seeds of asters, campanula, marigolds, cineraria, celosia, false Jerusalem cherries, morning glories. Pot tuberous begonias. May: Ventilate freely. Increase shading and damping down. Move seedlings of vegetables and flowers to cold frames, then into the garden. Transplant rooted cuttings to larger pots. Cut back stems of poinsettias; repot them and begin watering regularly. Pinch out young tips of fuchsia and chrysanthemums. June: Ventilate, damp down, and shade as needed. Water and mist freely. Take softwood cuttings of begonias, coleuses, geraniums, and fuchsia; pot them when rooted. Control insects. July-August: Sow seeds of cineraria (early July) acid calceolaria (late July). In early August sow seeds of lettuce, radishes, spinach, carrots, tomatoes, and herbs for growing in the greenhouse. September: Except on cold days, continue ventilating, watering, and damping down. Reduce feeding late in month; stop feeding plants that have finished growing. Sow seeds of annuals to flower in the greenhouse in spring; pot spring-flowering bulbs. October: Stop all feeding at month’s end. Reduce water for amaryllis bulbs. Remove summer shading except for ferns. Thin overgrown climbers. November.- Ventilate on sunny mornings. Except on unseasonably warm days, close all vents by midafternoon. Pot fall-sown annuals. December: Water as needed; ventilate on mild, sunny days.