A plant window can be as simple as a window with good light that has been modified to provide an extra-wide windowsill and additional shelves for plants. A plant window can also be a mini-greenhouse, complete with its own water, electrical, and sometimes even heating systems. A very complex plant window is usually called a greenhouse window, while a middle-of-the-road design is sometimes called a garden window. The plant window could be part of the original design of a new house, or it could be added to an older home.
Generally, a garden window or plant window extends out beyond the wall of the house to provide lots of sunlight to the growing area. The three exterior sides and the roof are glassed-in, and the glass roof is typically slanted. The base of the garden window often has a waterproof box built into it. Support brackets are usually attached to the exterior to help bear the weight of the unit and the soil it will contain when in use. The interior wall of the plant window may be completely open to the room, or it can have a glass door to create a hothouse environment.
In a house located in the northern hemisphere, a window for plants is usually positioned with a south or west exposure, to provide as much winter sunlight as possible for the window planting. In the summer, this can create too much heat inside the plant window. On a day with strong sunlight, leaves might be damaged. To prevent this, growers often install some kind of shade or blind. Some whitewash the glass to create filtered light.
Air circulation is necessary for healthy plants. A more elaborate plant window comes with a small fan to circulate the air. Many plant windows have glass panes that can be opened, especially on the side walls of the unit.
In cold climates, the plant window can become quite cold during the winter months. It should be large enough so that plants can be placed inside without touching the glass. Some gardeners use heat mats as well, especially if they are growing seedlings.