Vegetables can be grown year round even in cooler climates if you have a greenhouse. A warm greenhouse is heated during the cold months and should maintain a minimum temperature of 55 degrees F. Obviously this is a costly option for those in particularly cold climates, as natural gas and heating oil used to heat the green house are expensive. However there are many people who live in somewhat warm climates, where maintaining this temperature in the winter won’t be so prohibitive.
Keep in mind that in the summer a greenhouse may get too hot, and plants won’t grow properly so ventilation is necessary. In fact tomato plants will not fruit if the temperatures are maintained over 90 degrees F. Many gardeners will not try to grow vegetables through the whole winter, but instead will use a greenhouse to get an early start to the season. This way you can have tomatoes forming in June as opposed to waiting till late July or August. It is important to choose the correct variety of a vegetable that you will be growing in your greenhouse. There are certain varieties of tomatoes such as Legend and Siletz that will grow nicely in cooler weather.
Cucumbers, eggplant, squash, melons, carrots, lettuce, and peppers are all examples of vegetables that can be grown in a greenhouse. There are specific varieties of these seeds that are best suited for growth in a greenhouse. Keep in mind that you will have to pollinate your crops in the greenhouse as there are no bees to do the work for you. You can gently shake the tomato plants when the flower petals have a slight curve to them. Or you could use a small paint brush and manually pollinate all the flowers.
Since lettuce likes cooler temperatures it may be a good vegetable to grow in your greenhouse. In fact lettuce grows best when the daytime temperature is around 60F and the nighttime temperature is around 50 F. Lettuce has very shallow roots; therefore you must water your plants frequently. Initially you can start lettuce seeds in flats, and then when they are 3 inches tall they can be set in beds with a spacing of 6 inches by 9 inches apart.
Growing vegetables in a greenhouse is definitely a challenge that only an experienced gardener should try. You may not be successful your first season but that does not mean you should give up. As with anything else indoor greenhouse gardening will take practice and you will have to learn from your mistakes.