subject: Selecting A Greenhouse. [print this page] Choosing the right greenhouse isn't always easy, so here are a few pointers for you to help you choose correctly.
Traditional Greenhouse:
Vertical sides and an even span roof. Use of space and warmth is effective, and an enclosed lower part cuts down winter heat loss. Choose an all-glass model for growing-bag and border crops.
Lean-To:
Useful for the south or west facing wall. Bricks store heat during the day so the fuel bill is reduced. Most suitable option for a conservatory, an inter-connecting door makes it a part of the house.
Three-Quarter Span:
Lighter and much more airy than a lean-to, useful for growing wall plants such as Vines and Figs. Expensive, however, so the choice ought to be between a traditional house or lean-to.
Dutch Light:
Sloping sides and an even span roof, angled glass makes it warmer and brighter than a conventional house. Also more stable, but supporting upright plants from floor to roof can be more difficult.
Polygonal:
Many (6 - 9) sides, attractive when they are filled with pot plants and placed close to the house. Costly, however, and not a fantastic buy if you want maximum space for your money.
Dome:
Three advantages, good-looking appearance when filled up with flowers, maximum stability and maximum light absorption. One major drawback is the unsuitability for growing tall crops effectively.
Size:
A wide range of sizes are available. Standard sizes are from 6 to 20 feet long in widths of 6, 8 or 10 feet. The one you choose will depend largely on the money and space available to you, remember annual running costs as well as the original outlay. The most popular size is 8 ft. long and 6 ft. wide, if you plan to grow Tomatoes, the height to the eaves should be at least 5 ft. and the ridge height about 7 ft. Somewhat surprisingly, it is tougher to control the environment in a small house than in a large one. Increased size reduces the problem of draughts and sudden fluctuations in temperature.
Structure:
Aluminium has taken over from wood as the most popular building material. It is cheaper, easier to keep looking good and the thin glazing bars mean more light within the house. The drawbacks are quite minor - aluminium houses lose slightly more heat over night than wooden ones and the metal frame arrives in bits and so construction is rather more difficult.
Wood is considered by many people to be more eye-catching. If you go for a wooden construction buy Western Red Cedar, Teak or Oak. Cheap wood must be painted regularly with a long lasting preservative.
Galvanised iron houses are no longer popular. Paint them with a rust-destroying paint like Bio Rusty right away as the protective coating of zinc becomes scratched after a few years and rust will quickly set in and destroy the metal.
Glazing:
Buy glass not plastic. Glass is denser, heavier and not as safe as plastic but the benefits far outweigh the drawbacks. More light enters the house, less heat escapes and it is simpler to shade and clean. Polythene and PVC have a limited life, but if you do choose to go with plastic, make sure that it is UV stabilised. Glass has one major problem, it will break if hit by a heavy object. If you are near the road or a play area, consider polycarbonate sheets. They have many of the advantages of glass but are lighter and unbreakable. Regrettably, it scratches easily and is more expensive.
Doors:
Hinged or sliding - both types have their disciples. Sliding doors can be used as an extra ventilator and they don't slam shut. But hinged doors generally fit better and so are less liable to be a source of draughts.
Ventilators:
The ventilators on the standard model are usually inadequate. You need both a roof and side ventilator, their total area needs to be 10 - 20% of the total floor area. Louvred side ventilators are better than the standard hinged types, but ensure that they close properly.
