Good greenhouse vegetables are usually vegetables that don't freeze or keep well over winter and that can be grown close to their usual growing season in the greenhouse. Also, the most common greenhouse vegetables can usually be harvested quickly. For this reason and because they are usually somewhat cold-resistant, one of the most popular choices is leafy greens. Some examples include lettuce, Swiss chard, and a great deal of other leaf vegetables. Other good greenhouse vegetables include tomatoes, eggplant, and cucumbers.
Lettuce has most of the traits of the best greenhouse vegetables. It can be difficult to find good fresh lettuce during the winter, and garden lettuce doesn't keep long or freeze well. Leaf lettuce grows quickly in the greenhouse and can be planted weekly to make for a regular harvest. Greenhouse lettuce is usually planted in September through October or in January through February in later winter.
There are numerous other greens that, like lettuce, make good greenhouse vegetables. While it requires some space, spinach can mature in about 30 days. Swiss chard also does well and offers a unique and different taste. Salad greens like mesclun or arugula are good choices, as they are fast-maturing and can be quite expensive to buy out of season. Greenhouse bok choy, an Asian cabbage relative, can be harvested when it is immature or fully grown.
Tomatoes are often started indoors as greenhouse vegetables in order to be transplanted outdoors in May or June. Some gardeners start greenhouse tomatoes in January, while others may wait until February or March. Peppers and eggplant, which are related to tomatoes, are treated somewhat similarly. If these plants blossom indoors, the flowers will probably need help being pollinated in order to bear fruit. Gently shaking the plants may be enough to help them self-pollinate.
Cucumbers are also grown in greenhouses, but getting cucumber fruits requires transferring pollen from male blossoms to female blossoms. This can be done with a cotton swab or a small paintbrush. Some squash varieties can be started in a greenhouse for transplanting outdoors in early to midsummer. Radishes are another popular choice because they are easy to grow and can mature in about four weeks. Other crops to try include turnips and green beans.
The greenhouse is also a good place to try new varieties and practice growing vegetables. Some other plants are sometimes started as seedlings to be transplanted outdoors when the ground thaws. This could include seedlings for hardy plants such as cabbage, broccoli, and Brussels sprouts.