By growing vegetables in your own greenhouse, you can enjoy vegetables that are typically restricted by their seasons or because of your outdoor weather conditions. A greenhouse can extend your growing season by weeks if not months compared with traditional outdoor gardening.
But if you keep your greenhouse warmer, you will have more choices of what to grow. One way to get around this issue is to attach your greenhouse structure to your house, and share heat. For some areas, crops such as kale, carrots or spinach can grow outside with little protection. Parsnips grow well mostly anywhere unprotected.
Loose leaf lettuce does not form a head, but stays separately attached at the root. Varieties include green, red and oak leaf. Leaf lettuce can tolerate heat better than head-type lettuce, extending the growing season. Cut leaf lettuce when it is 3- to 6-inches tall. Named varieties are Salad Bowl, Slobolt, Black-Seeded Simpson and Red Sails.