What to consider before buying a greenhouse
Work out the best position for your greenhouse in your garden – ideally it needs to be in an open spot so that it gets as much light for as much of the day as possible. Trees will cast shade and stormy weather will bring the risk of falling branches breaking glass, so position away from trees if possible. A sheltered spot is perfect as this will reduce the problems caused by high winds.
When you’ve chosen your preferred location measure how much space you have, allowing for extra room around the sides for access for cleaning and maintenance. Consider the height too – you want to be able to stand upright, but you may also want to grow tall plants.
You’ll need to consider planning regulations – anything over 2.5m that’s within 2 metres of a boundary will need planning permission. It’s also worth checking with your local planning department to make sure there aren’t any local restrictions such as being in a conservation area or owning a listed building.
How do you plan to use the greenhouse?
Is it purely for growing or would you like some space to relax under cover from the British weather? Perhaps you’d like room for a chair or two, or maybe even a table so that you can dine in the garden but be sheltered on chilly summer’s evenings.
Think about what you’d like to grow. Is it just summer crops such as tomatoes and chillies? Or would you like to grow fruit trees such as peaches and apricots which will need more space. It’s easy to underestimate the amount of space you’ll need and buy a greenhouse which you quickly outgrow.
Will you want electricity in the greenhouse? If so, think about where you site the structure – close to the house will make installing a power supply easier and cheaper.
Location and style
There are a whole range of greenhouse shapes and styles from which to choose. Your choice may depend on your available space – lean-tos for instance are perfect if you want to utilise a south-facing house or boundary wall. Or it might simply be a question of personal taste – perhaps you’re happy with a classic rectangular structure or if the greenhouse is visible from the house you may be looking for something more decorative.
Glass versus polycarbonate is the next decision. Here are the advantages and disadvantages of both:
Advantages of glass:
- It looks more attractive because it’s clear.
- The plants are exposed to high levels of light.
- It can last a lifetime and isn’t degraded by the sun’s UV rays.
- It’s easy to clean.
Disadvantages of glass:
- In the height of summer, shading may be needed to protect plants from intense sunshine.
- Glass can break easily and can be dangerous, particularly if you have children or pets, although toughened safety glass is an option.
- Temperatures can fluctuate under glass, with very hot days and cool nights, which can be a problem for some plants.
Advantages of polycarbonate:
- The way it is constructed means it has insulating properties so temperature fluctuations aren’t such as problem.
- The opaque nature of polycarbonate means there’s no need for extra shading during the summer months.
- Because the temperature is more stable the growing season inside can be extended by 1–2 months.
- It doesn’t break like glass, so it’s a safer choice if you have children or pets.
Disadvantages of polycarbonate:
- It doesn’t look as attractive as glass because it’s opaque.
- You can’t see out into the garden when you’re inside.
- It’s degraded by UV rays, which means it has a lifespan of 10–15 years.
- The opaqueness means light levels are reduced, which will impact on plants in early spring and autumn, when light levels are naturally lower.
- It can be harder to keep clean as dirt and algae can build up, and these are harder to remove on polycarbonate than glass.
- Greenhouses made of polycarbonate tend to need more ventilation.
Wood and aluminium are the materials most often used to construct greenhouses. Think about the look you want and how the greenhouse will blend in with the style of your home and garden.
Aluminium is generally seen as more maintenance-free than wood, but if you choose cedar wood the greenhouse can last up to 30 years. The reason why cedar is so durable is that it contains natural rot-resistant oils and while it absorbs moisture in the air just like other wood, it dries out faster.
There is a difference when it comes to price – an aluminium frame will be less expensive than a wooden one.
Aluminium can come in the bare silvery-coloured metal or can be painted green, black or anthracite grey.
A solid, level base is important as it will provide stability for the structure. You can choose to lay paving stones which will provide a degree of insulation and make it easy to keep the floor clean but you won’t be able to plant directly into the soil. A cast concrete base will have 10–15cm of concrete edge inside the greenhouse, whereas a steel base will be the same width as the greenhouse frame.
For more inspiration go to greenhouses.com or juliana.com
Om Nanna Stærmose
Nanna is the Danish writer of many of the articles in the Greenhouse Forum.
Nanna visits happy greenhouse owners and tells their stories about basic cultivation, but also those stories that are more oblique.
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