Where to Build a Greenhouse
To be the owner of a successful greenhouse, you need to spend at least as much time and thought on where to site it as on which type to choose. Equally, attention to detail when laying foundations and erecting the structure will amply reward the extra time spent.
In most cases it is wise to choose an open position for the greenhouse where it will get as much sunshine as possible. This generally means that you should try to position the unit with one of the longest sides facing south. It is a simple matter to shade the glass when you want to reduce light entry, but it is difficult to increase light without the trouble and expense of artificial lighting.
Remember that, in winter, nearly all plants will enjoy plenty of sunlight — even summer shade-lovers. Winter sunlight also means plenty of free warmth and your heating costs will be reduced.
Shady and windy sites
Avoid, where possible, a site that is near large trees (especially evergreens). Falling branches may break the glass, and spreading roots may upset the foundations. Falling leaves and exuded gums from some species dirty the glass, and you may also find that the roof is covered with bird droppings. Evergreens cast shade all year round, and many trees harbour numerous pests and diseases that can attack greenhouse plants and crops.
Small shrubs and trees are not usually a menace; these can even be planted (far enough away so that they do not cast shade) to act as windbreaks in windy areas. Strong, cold winds, usually from the north and east, can add greatly to the fuel bill. Other suitable windbreaks are fences, walls and hedges — as long as they are not too high.
Low ground and hollows
When choosing a site for your greenhouse, look carefully at the ground contours of your garden. In all cases where the site is at the foot of a hill there is a danger of frost pockets forming. Cold, frosty air can run off a slope almost like water, and surround a greenhouse that is set in a hollow. Where no other site is available, a low brick wall can help to deflect icy air currents.
In hollows and on low ground, water may collect or the ground may become very damp. These conditions are particularly unhealthy in winter when the greenhouse should be as dry as possible.
Sites near the house
Many people put their greenhouse at the far end of the garden — some distance from the house. There is often no good reason why it should be tucked away out of sight. Modern structures are rarely `eyesores’ and some designs are very attractive, especially when filled with decorative plants. There are many advantages in having the greenhouse within close reach of the house. Both water andcan be run to the greenhouse easily. Electricity, even if you don’t want it for heating, may be needed for automatic aids or lighting; you may also wish to run natural from the house.
When the greenhouse is to be heated by solid fuel or paraffin, remember that the fuel will have to be carried to the greenhouse and, in the case of solid fuel, the ash carried away — yet another reason for avoiding remote sites. If you don’t want to see a greenhouse from the windows of your home, you can always screen it with low shrubs or small ornamental trees.
In some cases greenhouses can be heated economically by an extension of the sameused in your home. In this case the greenhouse should, preferably, come into contact with the house wall, and a lean-to is usually the best design. Where high temperatures are required it is always an advantage if the greenhouse can be set against a house wall, or a south-facing garden wall. Such a wall usually absorbs warmth from the sun during the day and radiates it at night, thus saving fuel and acting as a kind of free storage heater.
Laying the foundations
Most modern, prefabricated, amateur greenhouses are easy to erect single-handed, though with the larger sizes you may need assistance. The ground must always be firm and level, so laying a shallow foundation (by digging a trench and filling it with a fluid concrete mix that finds its own level) is often a wise move. However, some greenhouse manufacturers recommend their own base plinths and the small additional cost of these is well worth while. Some designs do not need elaborate foundations but are secured by ‘ground anchors’. A separate hole is dug for each anchor and the framework is then bolted onto these before the glazing is put in.
Brick or concrete base walls, if required, are best constructed by a professional builder — unless you are reasonably expert in this sort of work. Greenhouse manufacturers always provide a detailed ground plan of the structure, so follow this closely when putting in foundations or base walls.
When erecting your greenhouse, use a spirit level and plumb line to make frequent checks on levels and verticals.
Fitting the glazing
Stand glass panes in a dry, covered place until you are ready to use them. If they get wet they are very difficult to separate and you risk breaking them. Glazing is best done when the weather is not too cold or your fingers may be too numb for careful handling. Do any metal or timber painting before the glass is put in. If you are using putty, only put it below the glass as a bed for the panes — not over the top as well, as in ordinary domestic glazing.
Be especially careful, when erecting and siting plastic greenhouses, to avoid possible wind damage. The suppliers usually issue special anchoring instructions and recommendations. When plastic is to be fastened to a timber framework, don’t use creosote preservatives on the wood. Some plastics will become weakened by contact and all will be severely discoloured, making the greenhouse most unsightly. Moreover, creosote fumes are harmful to plants. For the same reason creosote should not be used on any timbers in close contact with plants in a confined area — such as in greenhouses or frames. Instead use one of the proprietary horticultural timber preservatives on the market.
Tending the site
The surroundings of your greenhouse should be kept tidy and weed-free. Weeds will harbour many troublesome pests: for example nearby stinging nettles may bring you an infestation of whitefly.