Gardening in a greenhouse

Owning a greenhouse can give you the opportunity to grow plants from all over the world. But before you stock up on potted citrus, orchids, cacti, scented geraniums and bromeliads, you need to stop and think about what sort of growing environment you will actually be able to provide. A common mistake made by beginning greenhouse gardeners is to fill the greenhouse with any plant that piques their interest.
An eclectic assortment of plants such as this may look fine for a few months, but they will soon begin to suffer. Some plants need cold nights, some need warm nights. Some like lots of bright light, some require filtered shade. Some need water twice a day, some only every few days. The challenge is to decide what sort of environment you will be able to provide, to take advantage of the microclimates within the greenhouse, and to choose plants that will thrive in those conditions.
If you plan to run your greenhouse year-round, you first need to determine what temperature range you want to maintain - both in winter and in summer. Wintertime temperatures ranging from 40 to 60 degrees F may be ideal for growing salad greens, herbs, and for overwintering tender exotics. But these temperatures are too cold for producing healthy tomatoes.
During the summer months, bright sun and daytime temperatures of 85°–90°F may be fine for potted tomatoes, bananas, and figs, but alpine plants, and many types of veggies will not tolerate the heat.

Microclimates
Within any greenhouse, there are certain areas that are hotter or cooler, brighter or shadier. By taking advantage of these natural microclimates, you can provide optimum growing conditions for a wider range of plants. Shade cloth, lathe, small fans, propagation chambers, heat mats, and other devices can also be used to help create and manage these microclimates.
Your climate, the type of greenhouse you have, and the amount of time and money you are willing to invest in heating and cooling, will determine what sorts of plants you'll be able to grow successfully.

Resources
Greenhouse Gardener's Companion by Shane Smith
The Greenhouse and Nursery Handbook by John Gist.
Secrets to a Successful Greenhouse and Business :A Complete Guide to Starting and Operating A High-Profit Organic or Hydroponic Business That Benefits the Environment

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