Installing a Greenhouse

To get the best out of your greenhouse, decide first on the right position and then establish firm foundations of the correct size well in advance of construction. If you are erecting the structure yourself, choose a fine day when you and your helper are not pressed for time.

The Best Position

A greenhouse needs to be sited in an open position, away From overhanging trees, and where it gets the greatest amount of sunlight, particularly in the darkest winter months. Have the ridge of the roof running east to west. This will allow the maximum amount of light to enter, while casting the smallest amount of shadow, especially when the sun is low in the sky. If you want mains electricity installed, it will probably be more convenient to site the greenhouse fairly close to the house or mains supply.

Good Foundations

Greenhouse foundations and bases vary, depending on the type of greenhouse and the manufacturer's specifications. It is important that the foundations are strong enough to support the weight of the structure and that they are level. Often the base comes as part of the kit and is fixed to anchor pins buried in the ground; it should be capable of anchoring the structure in windy conditions and preventing it from lifting. Other greenhouse models will need a concrete or brick plinth.

If the lower part of the greenhouse sides are to be built of brick, you need to construct permanent foundations as for a patio. If you want to accommodate soil borders within the structure, the foundations must correspond exactly to the greenhouse measurements given by the manufacturer. If in any doubt, discuss the requirements with the supplier. At this stage you could also lay down concrete or paving slabs to make the permanent central path, which should be no less than 60 cm (2 ft) wide.

An alternative to having soil beds is to construct an entire solid floor of slabs or concrete over a hardcore foundation, in which case the base should extend beyond the greenhouse on all sides to spread the weight and help to reduce settlement later. Or the floor to either side of the path can be covered with a layer of gravel over a weed-proof membrane.

Although many suppliers offer a construction service, it is not difficult for two people to erect a small greenhouse. Read the instructions before you start. Begin by unpacking the sections and check that all items are present and correct. Each section will come as a numbered bundle: lay these out in order of construction.

Equipping a Greenhouse

The basic equipment needed to get your greenhouse up and running is some shelves and staging, and you wil have to decide whether to heat your greenhouse as well as make sure that the ventilation is adequate.
soil borders and containers.

You can grow your plants either at ground level, directly in soil borders, or in containers, or raised on staging, where it is often easier to work and to check on your plants. Soil borders are suitable for growing some plants such as winter salads, tomatoes and melons, but you have much less control over the growing environment than when using containers or growing bags. The main problem with growing in border soil is the build up of soil-borne pests and diseases. To keep the soil healthy it should be revitalized annually with organic matter and every few years replaced to a depth of around 60 cm (2 ft).

Staging

Greenhouse staging, or raised shelving, can be made of aluminum, concrete, brick, steel or wood. Strong supports are essential, as they must bear the considerable weight of plants, compost, and possibly wet sand or gravel. The surfaces or shelves can be solid or open.

• Solid tops: These come in wood or sheet metal. Sheet metal trays with a 2-3cm (1 in) rim can be filled with sand or gravel to help watering in summer, as pots can take up moisture from the trays by capillary action.
• Open tops: These may be wooden slats or a form of wire mesh. Their advantage over solid tops is that they allow better air circulation around the plants.

Ventilation

Greenhouses usually have at least one vent, but you will probably want to supplement this. The best combination is to have ventilators in the sides and the roof to create a chimney effect, as cool air enters through the side vents and is expelled through the roof vents as it warms. A change of air equivalent to two or three times the volume of the greenhouse each hour is ideal, and the total area of vents should equal one-sixth of the greenhouse floor.

If you are out for much of the day it is worth installing automatic vents, which open and close as temperatures rise and fall. You can also buy louvred panels for fitting in side walls. Leaving the door open on warm days provides extra ventilation. In very hot weather you could also install an electric extractor fan to move air through the greenhouse. These can also cool air in summer by passing it over wet pads.

Heated or Unheated?

A wide range of plants can be grown in an unheated greenhouse, but most of the growing will take place between the beginning of March and the end of October. You may need to provide some protection over winter, but this will not necessarily be enough in extreme conditions, when plants inside can be frost-damaged. A compromise can be achieved by growing plants mainly in an unheated greenhouse, but providing some heat as frost protection through the winter or very early spring.

It is easy to heat a greenhouse, but it can be costly. Check that the greenhouse is:

• Well maintained in order to exclude drafts and heat leak.
• Well insulated during winter months by lining the walls with bubble plastic. At night lowering shading blinds helps to retain heat, but raise them every morning.
• Divided into sections, so plants that require high winter temperatures are grouped together in one well-insulated area that is heated, leaving the other area unheated for hardier plants.

If you plan to install heating, decide on the kinds of plants you wish to grow and the temperature regime they prefer. Buy a maximum-minimum thermometer to monitor temperatures.

• Frost-free conditions mean a minimum temperature of 5°C (40°F).
• A temperate house heated to 10°C (50°F) allows many plants to grow through winter, but costs twice as much to heat as a frost-free house.
• A tropical regime of 15°C (60°F) is preferred by most houseplants, but can be five times as expensive to heat as maintaining a frost-free house.

Heating Methods

• Electric heaters are very efficient and many have thermostatic control, which reduces their running costs. Fan heaters are fast-acting and also circulate the air. Tubular heaters are cheaper and equally portable. A mains supply is essential and should be installed by a qualified electrician. Never run an electric heater off an extension lead from the house.
• Gas heaters require good ventilation. Propane gas heaters are portable but need checking regularly. Have at least one full cylinder in store. There are models that run off natural gas, but a qualified gas fitter must install them.
• Paraffin heaters are cheap but discharge fumes, which can harm some plants, and also water vapour, so good ventilation is important. They also need regular refilling and maintenance. They are most useful in small greenhouses, heated propagators

These are electrically heated closed cases with bottom heat used to germinate seedlings or root cuttings. They should have a thermostat to monitor the temperature within this enclosed environment. You can create your own by installing a heating mat or cables on solid staging and covering with a small portable frame or cloche.