As further proof that many plants prefer freedom to being confined in pots, try planting just one creeper—an episcia, for example—in the center of a spot filled with suitable soil. See how soon it will garland the top with lush foliage, how freely it flowers. Many plants recommended for hanging baskets are really creepers and are better off when treated this way.
PLANTING AND CARE
Large or small, a greenhouse garden, like any other, should be designed carefully and never planted until you have the plan firmly in mind. Each plant should be given room in relation to all the others, and not merely at planting time but with maturity time in mind. Allow plenty of space for spreaders to spread and creepers to creep; and make sure every climber has its support. And, of course, plants in close proximity should have compatible cultural preferences in soil, moisture, light, and the like.
Light and Sunlight
It shouldn’t be difficult, in a complete greenhouse garden, to arrange for areas of full sunlight, partial or dappled sun, and shade, and to do it in a natural manner. Tall plants will get the sun first and for the longest time; but you could also build a slope, a sand dune, or a rock garden that would face the sun and get the most of it. Partial-sun plants could be placed where they are only lightly shaded by other plants or, if necessary, by shadings on the sections of glass above them. Shade-loving plants can grow under small trees and bushes.
Almost any greenhouse, in any area, should have shading applied to the glass in early summer. Several shading compounds are available, in white or green, and are mixed and applied with either a wide brush or a sprayer. These compounds are constituted so that they slowly weather away during the summer and leave the glass clear by autumn. But if you happen to have plants that need all of the winter sun possible, it is wise also to clean the glass.
Temperature
Greenhouses are generally classed as cool (40–60 degrees), moderate (50–70 degrees), or warm (60–80 degrees). This refers to the minimum night temperatures at which the thermostat is set to regulate the furnace or heater. In warm climates where an air-conditioner is used, it follows the same scale. Greenhouse plants are usually classified similarly. But if other cultural conditions are favorable, many plants will tolerate a much wider range.
In order to grow the widest variety of plants, I set my greenhouse thermostat at 60 degrees in winter. This is a little warm for some cool-growing items such as geraniums, and causes outdoor garden plants (annuals, perennials, and vegetables started from seed) to grow slightly leggy and lank. But they recuperate in a hurry when they are moved outside. This temperature is slightly cool for subtropical plants; some gesneriads merely hold their own through the winter, neither growing nor flowering; some extremely tender begonias are forced into dormancy, from which they awaken in warm spring weather.
Humidity and Ventilation