Choosing a Greenhouse

Summary: How to choose a greenhouse, different types of greenhouse, materials used, building a base for your greenhouse.

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A greenhouse is a very useful addition to your garden or allotment, but choosing which one to buy is a difficult decision. Size, style, construction, price, even colour – all these are things you’ll need to consider.

Reasons for Buying a Greenhouse

Firstly, think about what you are going to use your greenhouse for, as this will have a bearing on the size and other aspects of your choice.

If you like to grow your own fruit and veg, a greenhouse will extend your growing season – allowing you to plant seeds earlier while the ground outside is still cold. Some crops need the heat and protection of a greenhouse to grow, so you will have a wider range of varieties to choose from if you decide to add one to your garden. Tomatoes, sweet peppers and cucumbers are all greenhouse favourites.

Traditional style greenhouse

Traditional style greenhouse

If flowers are your passion, a greenhouse will enable you to care for tender varieties and will prove invaluable for propagation.

Location

Where is the best place to situate your greenhouse? Obviously, it will need a good deal of sun so you need to pick a spot that’s not too shady. If your garden is quite exposed, try to avoid locating your greenhouse in the way of a cold northerly or easterly wind. Not only is a strong wind liable to cause damage, but a cold breeze will affect your plants.

Size

If you are planning on having a few grow-bags, you’re going to need a fair amount of space. Don’t choose a greenhouse that’s going to take up your whole garden though! There’s a delicate balance between the amount of space you need and the amount you can afford. When thinking about the size of greenhouse to purchase, keep in mind that it’s useful to have space for a worktable – an area where you can pot-on seedlings etc.

The higher the greenhouse roof, the more effective it will be – a good, sloping roof space enables excess heat to be dispelled. If you are going to be working in the greenhouse a lot, make sure you have enough space to stand up and move around comfortably.

If you have a very small garden, greenhouses are available as small as 4ft x 6ft, and if even that’s too big, you might consider a mini growhouse. See below for more information on types of greenhouse and growhouse.

Types of Greenhouse

Mini Growhouses

Usually constructed from a tubular frame with a plastic covering, these are ideal for anyone with a garden too small for a full greenhouse. There are a variety of sizes available, from about 70cm wide and 50cm deep. They have a number of removable shelves, allowing for trays of seedlings or taller plants. Be aware that these growhouses are generally quite flimsy and will need fixing to a wall or fence.

Lean-to Greenhouses

A lean-to is the next step up from a mini-growhouse. If you have a small space next to the house or garage, adding on a lean-to greenhouse can be a good, space-saving compromise. Having one wall made of brick means that a lean-to isn’t quite as efficient as a free-standing greenhouse, but brick will hold in heat well, meaning that it will stay warm late into the evening.

There are a massive range of sizes and styles, from simple little 2ft x 4ft aluminium versions up to luxurious 8ft x 20ft wooden frames, with everything in between.

Free-standing Greenhouses

Free-standing greenhouses are available in almost any size imaginable, from a little 4ft square model up to giant 10ft x 20ft and even larger. Whatever space you have available, you can be sure to find a greenhouse to suit it. Smaller greenhouses generally have a single sliding door on a gable end, while larger models will usually have a double sliding door. Exceptions are wooden-framed versions, which sometimes have a standard hinged door.

Most metal-framed greenhouses are of a similar basic style, although there are now versions available with curved rather than angled eaves. Wooden-framed greenhouses have a bit more variety in shape.

Materials

Aluminium or wood are your main choices for the greenhouse frame. Galvanised steel was used before aluminium became popular, and is still available in a few places. An aluminium frame requires much less maintenance. Timber frames require painting or staining every few years. Metal frames are often available powdercoated in green or white now, which enables you to choose a finish that will blend in with the surroundings.

When it comes to glazing, there are now a few options available. Tempered safety glass is harder to break and a safer but more expensive than standard horticultural glass. Polycarbonate is a popular but more expensive glazing option - the fact that it is shatterproof and has good insulation qualities makes it worth the extra money, however beware of inferior quality versions – some cheaper polycarbonate panels may only be 4mm rather than the usual 6-8mm thick, and may not have exterior treatment, meaning that it can discolour and become brittle. A few cheap greenhouse manufacturers use acrylic glazing, but this is to be avoided as it is flimsy and does not last well in the elements.

Base

If you are buying a new greenhouse, complete sets with frame, glazing and base are available. The term ‘base’ can be a bit misleading – this is a four-sided galvanised steel upframe, which the greenhouse fits on top of, and allows you to fix the greenhouse directly onto a concrete foundation (see our building a shed base project to find out how to make one) or slabs. If you are planning to use slabs, make sure they are securely bedded in as any movement will put stress on the greenhouse frame. Our laying a patio project will help you with this. If you have bought or inherited a second-hand greenhouse it may not be possible to find a base of the correct size, in which case you can make your own base using bricks.

Accessories

Auto-vents are a worthwhile investment, allowing the windows of your greenhouse to open automatically when a certain temperature is reached. Ventilation is vital to plant growth, and opening and closing windows and vents every day can get tedious.

Lightweight staging tables are good for sitting pots and growbags on. Shading material is required to protect plants from being scorched by direct sunlight when the sun is at its strongest. If you plan to use your greenhouse throughout the winter, a heater and insulating material will be needed. Rainwater kits can be fitted onto guttering, draining into a water butt to give you a ready water supply. See our installing a water butt project. Whatever water supply you have can be used in conjunction with a drip watering system to ensure your plants never go thirsty.

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