urchasing a greenhouse represents a significant investment, but there’s a huge variety on the market, with considerable differences in size and specification. Read on to discover GardenSite’s guide to the most frequent questions on greenhouses that are asked by their customers.

1. Timber or aluminium frame, which is better?
There are pros and cons to both types. Timber is considered traditional, easy on the eye and quick to blend in with the garden. In practical terms, it offers better insulation and is consequently cheaper to heat than aluminium. Anodised or powder-coated aluminium doesn’t rust, and it is also worth bearing in mind that rot-resistance can be built into modern timber by a number of different treatments. If you can afford cedar, that will last for many years without attention. This brings us to the issue of cost – aluminium greenhouses are cheaper, lighter and easier to assemble. Frames in this material will let in more light, but condensation may be a problem.

2. Should I choose a freestanding or lean-to structure?
That depends on the size of your garden and how many plants you want to grow. Freestanding greenhouses naturally allow in more light from each side, and there’s more room for shelving and staging, plus a greater growing area. Curved glazing and ‘barn’ styles offer height for tall plants, and there are also freestanding circular and lantern-shaped models. Conservatory and lean-to designs clearly take up less space and suit a compact garden. The back wall can be painted white in the traditional manner to slightly make up for less light. The wall will also retain heat and can support climbing plants. With an internal door into your house, a lean-to can be very convenient, especially if you are disabled, as it becomes a conservatory and you needn’t go outside to tend your plants.

3. Is bigger better?
A qualified answer would be to choose the biggest structure that your budget will allow and your garden can accommodate. Any greenhouse will quickly fill with plants, pots, bags of compost, tools and equipment – there’s nothing more frustrating than buying small only to find out later that you could have chosen a larger example. However, you probably don’t want your greenhouse to totally dominate the garden, and the type of plants you want to grow should also be considered.

4. What’s the best location?
A site with a firm foundation, preferably slabs or concrete, that is easily accessible. Make sure it’s in a sunny position with the longest side facing south. Greenhouses need some shelter from high winds and the cold, so the door should face away from the prevailing wind. For practical reasons it should be near a source of water and preferably electricity. Do not locate it under a tree, in a frost pocket or in the shadow of a building.

5. What type of glazing should I choose?
There are generally three choices. Standard horticultural glass is the cheapest option – this has good light transmission but breaks easily into shards, so it can be dangerous and shouldn’t be used if you have children. Toughened safety glass is stronger and will disintegrate when broken. Polycarbonate is more expensive, but offers superior insulation. It’s hard to break, but lets in less light, approximately 85 per cent, and can have problems with condensation.

6. What ‘extras’ are necessary?
You should consider investing in staging for potting and sowing seed, bubble wrap for winter insulation, blinds or shading paint for the summer, guttering, and a water butt to recycle rainwater. You may also wish to purchase capillary matting for irrigation, a min/max thermometer to accurately control temperature, and automatic ventilation for when you go on holiday.

7. Is heating required?
Probably, especially as greenhouses have poor insulation and you want to overwinter tender plants. Maximise the use of your structure by starting off plants early in the season and growing the largest varieties. Temperatures should not be allowed to drop much below 10°C, and daily variation should not exceed more than that figure either way. You can manage the heat by installing ventilation, insulation and heating – the latter can be achieved through electricity, gas, or paraffin. Electricity is reliable, clean, and accurate with good circulation if a fan heater is used. Gas can give off fumes, cause condensation, and a spare cylinder must always be available. Paraffin gives off fumes, doesn’t enable you to accurately control the temperature, needs frequent maintenance, increases humidity and causes condensation.