A greenhouse is an asset to any garden and essential to many for the propagation of seeds and plants and for providing suitable growing conditions for a wide range of plants that would be unable to survive in the external environment. In order to obtain maximum benefit from a greenhouse it is necessary to understand certain factors when embarking on the construction, equipping of and working within a greenhouse.

POSITION

It is important that as much light as possible enters the greenhouse, therefore consideration as to the position of the structure is required. Tall trees, boundary fences and walls can create shadows, obstructing light, so thought is required as to how much sunlight is available all year round, not just the summer months. A greenhouse facing south is ideal if it is a lean-to structure against a wall. However, free-standing, independent structures should be placed east – west in order to avoid the lattice blind effect on conventional apex structures and gain maximum sunlight during the winter and spring.

CHOICE OF MATERIALS FOR THE GREENHOUSE STRUCTURE

The choice of materials is normally limited to either wood or aluminium, although less expensive structures based on alloys and plastic are available for the amateur market. Wood is a traditional material and can appear more attractive in some gardens. However it requires periodic upkeep and more general maintenance. The advantages of aluminium are that they need no upkeep, and the structural frames are thing, casting very little shade. Aluminium, either bare or painted (usually powder coated) may also fit into the garden better, especially if the structure can be seen from the home.

GREENHOUSE TEMPERATURE

To make the most of a greenhouse it is advantageous to use additional heat. For smaller greenhouses it is best to invest in an electrical fan heater with a thermometer switch to achieve the desired temperature. Many commercial structures often use blown heat, but for large domestic structures a hot water pipe system with a boiler powered by either gas or oil is the norm. Thermostats for the system should be located at plant height near the centre of the greenhouse where they are not influenced by drafts or sidewall cooling and protected from direct contact with sunlight and water. These devices are energy saving and even simple models can provide different daily temperature settings that automatically lower the night temperature and raise it in the morning.

VENTILATION

Often the suns rays can cause the greenhouse to become overheated between spring and autumn, which can lead to the plants becoming stressed. It is well known that hot air rises, so this is the easiest route for any hot air to exit, via the roof ventilation. The process is improved with the use of vents that open in the sides of greenhouse. Automatic ventilation will assist in providing stable temperatures. A simple calculation of 25% of the floor area will ascertain the minimum amount of opening vent space that is required. Remember, if you feel uncomfortable in your greenhouse, and then so do your plants.

LAYOUT OF THE GREENHOUSE

WALLS

Many plants can be grown against the back wall of a greenhouse. Fruit is a popular choice producing a large crop in a small space, using traditional fruit training techniques. Ornamental plants can also be grown in this space e.g. Pelargonium, and any number of climbing plants from warmer climes such as Bougainvillea.

BENCHING

Some form of benching or staging is essential for providing an area to support growing plants and potting on. The staging needs to be strong and capable of supporting the heavy weight of pots laden with plants and moisture. Freestanding benching is the most popular and can be constructed of slatted wood (cedar) or aluminium. Aluminium has the advantage of longevity and requires no maintenance. They should not be too wide and stand about the same height as a kitchen worktop (90cm). Ensure that they are level and that there is enough room for access and to undertake work on them. Many garden greenhouse manufacturers produce staging and shelf equipment specially made for particular greenhouses, but there are independent manufacturers that supply ranges to fit all greenhouses.

CAPILLARY MATTING

Capillary benches are widely available and allow crops of similar plants and pot sizes to be kept evenly watered right the way through the day. This is constructed using a normal flat bench with 5cm-raised edges. The surface is lined with capillary matting, which goes over the side of the bench into a vat of water. The capillary matting will draw up water and remain damp so that pots placed on the surface of the capillary matting will maintain a steady moisture level throughout the day. Additionally liquid fertiliser can be added to the water vat thereby automatically feeding and watering the plants. Lower benches are handy for those plants that are resting, such as corms e.g. Cyclamen and tubers e.g. Achimenes (Hot water plants). Remember to check on them from time to time. Also they are convenient for storing items such as the watering can, sticks for plant supports and spare pots.