Greenhouses extend the growing season and allow you to try plants difficult to find your area. Successfully growing plants in a greenhouse requires knowledge of soil, plant nutrition, environmental conditions to meet a plant's needs and pest management. Some greenhouse plant choices depend on how much money you have to spend on indoor environment control. For example, in the South if you want lettuce in July, you need to air condition your greenhouse. In winter climates, greenhouses require heat to maintain temperatures warm enough for plants to survive.
Lettuce, spinach, baby salad greens and mesclun grow well in greenhouses. Consider adding colourful salad items such as red-leafed lettuce and chard to your greenhouse plants. Alternatively, try unusual or expensive salad vegetables or those not always available in your supermarket, such as radicchio and arugula. These plants mature quickly in a greenhouse setting, and you can harvest a plant two to three times during its growing period.
Greenhouses provide an excellent environment to start seeds that you will later transplant into the garden. Because seed packets offer a much greater selection than the transplants available in your area, you can experiment with new types of tomatoes, peppers or eggplant. You can start annual flowers from seeds to add to your landscape after the last freeze. Warning: root crops and legumes -- beans and peas -- do not transplant successfully, so they must grow to maturity inside the greenhouse.
Annual herbs, such as basil, can spend their entire lives growing in a greenhouse. However, perennial herbs, including thyme, mint and oregano, prefer being outdoors in warm weather and inside the greenhouse the remainder of the year. Selecting the herbs to grow in your greenhouse depends only on the types you want for cooking or fragrance.
Orchids are premier greenhouse flowers that will happily spend their lives inside a protective environment. However many flowers start successfully in a greenhouse for later transplanting outdoors. Start calendula, carnations, chrysanthemums, marigold or zinnias in the greenhouse in winter. Start lily plants including African lilies, Plantain lilies and dwarf lily varieties, and transplant after the risk of freezing temperatures passes. If greenhouse space is limited, select flower types that need special care or are difficult to find as transplants in your area.