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A guide to choosing a greenhouse


A greenhouse extends the gardening year. The protected environment enables the gardener to grow a far wider range of plants than can be grown outdoors.

A greenhouse extends the gardening year. The protected environment enables the gardener to grow a far wider range of plants than can be grown outdoors. Frost-tender plants can be overwintered, seeds can be sown earlier in the year for earlier produce, exotic tender plants can be raised and sun-dependent vegetables such as tomatoes and aubergines grown to perfection.

Choosing a greenhouse is a big decision and beforehand the following factors should be considered:

  • Before choosing the type of greenhouse you want the correct site should be selected.  It should be sheltered from strong winds, but it should be in a position to receive plenty of light.  Greenhouse shading can be easily be provided if sunlight gets too bright and strong.  Avoid a site in shade or near trees as they could not only cast shade but may drop leaves and other plant debris onto the glass and become a nuisance.  Choose an area with space enough around the house for maintenance and cleaning.  If you are going to use electricity, bear in mind it may be easier to install it if the greenhouse is close to the house.

The next thing to consider is what the intended use of the greenhouse will be - Will you need heat in the greenhouse? What you grow will affect whether you need heat or not. If you want to grow plants from seed earlier in the year and extend the growing season through the autumn, then you will need to heat the greenhouse. A thermostat working with an electric fan heater will keep the temperature frost-free and the fan heater is useful to circulate air on damp days to prevent mould. A little extra heat will allow you to grow frost-tender plants such as citrus fruit and abutilon. If you need to install electricity, do it at the start when the base is being laid. Alternatively, a propagator with a thermostat and bottom heat can nurture seedlings, while bubble insulation will also provide some insulation.

If the greenhouse is to be in full view of the house, consider an attractive wooden model or a well-constructed aluminium design. If it is out of sight, then a functional house with an aluminium frame maybe adequate.  Your choice of greenhouse construction may  depend on budget - wood is more expensive than aluminium, but if you choose wood, make sure it has been treated properly against rot. Wood will need maintenance, aluminium will not. A hardwood such as teak or cedar will last better than softwood, but is expensive.

Ideally toughened safety glass is the best choice for a greenhouse because it allows in the most light, and is more durable than synthetics products. If it does get broken, glass is also easier to replace than plastics.

.......... And what size greenhouse should you choose

If you are a keen gardener, try to choose a large greenhouse to meet all your needs. 

Compact greenhouses, where you can barely stand up are not a good investment. A greenhouse should be at least 1.8m by 2.4m if you want to have staging on either side. It sounds obvious, but allow for at least 30cm above your head at full height, there needs to be plenty of head room not just for your comfort but also, for training tomatoes and cucumbers too.

Domes, octagons and unusual shapes of greenhouses can be both difficult to maintain, ventiliate unevenly and have hot and cold spots.  They also tend to be more costly than the traditional greenhouse shapes. A lean-to with a slanted roof is a practical option where space is limited.

Other practicalities to think about - The door must be wide and tall enough to carry a tray of plants or a tall plant comfortably. Hinged doors must be held open or secured; a sliding door is simpler to use and uses less space.  A soil border is useful to grow plants direct, and can be covered with staging when not in use.  Staging around the greenhouse should be at waist height.  Ventilation must be adequate: side and roof vents are necessary to ensure the greenhouse is properly aired in summer.  Guttering and a water butt should be installed so that rainwater is not wasted and can be used directly on plants.

Tip:

Try using our Coolglass greenhouse shading to protect plants from summer sun. To apply, just mix a sachet with water and brush or spray on. At the end of the summer, it is easy to wipe off to allow maximum sunlight into the greenhouse. Another useful product to use in the greenhouse are Greenhouse Flycatchers which are sticky cards which can be easily tied to the structure of the greenhouse close to those plants which are susceptible to aphids and whitefly, such as tomato and cucumber plants.  The yellow and blue colours of the cards attract both thrips and whitefly, aswell as other flying insects such as aphids.