Summary: Advice discussing what to consider when buying a greenhouse, discussing greenhouse styles & sizes, where to position your greenhouse, aluminium vs wood, assembling & installing a greenhouse, planning permission and basic maintenance.
Would you like to make better use of your garden and extend the growing season? Would you like to grow those tender plants that can’t withstand our winters in the open? Would you like to grow your own bedding plants from seeds or enjoy a constant supply of fresh flowers and vegetables? Does the thought of early strawberries or just-picked late tomatoes sound tempting? Then a greenhouse is definitely a good idea. Affordable and easy to install, they come in a variety of shapes and sizes.
Greenhouse styles and sizes
There are many different greenhouse styles and sizes. We will discuss the advantages and disadvantages of 6 common types of greenhouses.
- Traditional greenhouse
- Barn style roof greenhouse
- Lean-to greenhouse
- Heptagonal greenhouse
- Cold frame greenhouse
- Clear polythene groracks greenhouse
Advantages of a traditional greenhouse
- Generous growing space.
- Easy to work and move around.
- Blends well into the surroundings.
Disadvantages of a traditional greenhouse
- Can be costly to heat in winter.
Advantages of a barn style roof greenhouse
- Generous headroom.
- Generous growing area.
- Ideal for growing taller plants.
- No base required.
- Attractive shape.
Disadvantages of a barn style roof greenhouse
- Can be costly to heat in winter.
Advantages of a lean-to greenhouse
- Great when space is limited.
- Ideal if the only supporting building is single storey.
- Heat efficient.
- Convenient if erected against a house wall.
- Could double as a conservatory but not recommended.
Disadvantages of a lean-to greenhouse
- Requires a supporting wall.
- Robbed of light if north facing.
- Could overheat in summer if south facing.
- Will need additional ventilation and shade blinds, especially if south facing.
Advantages of a heptagonal greenhouse
- Ideal for a small space.
- Decorative shape.
- Suitable for positioning on a patio.
Disadvantages of a heptagonal greenhouse
- Limited growing space.
- Confined working area.
Advantages of a cold frame greenhouse
- Easy to move.
- Easily assembled.
- Very affordable.
- Protects plants from frost.
- No base required.
Disadvantages of a cold frame greenhouse
- Limited scope.
Advantages of a clear polythene grorack greenhouse
- Easy to move.
- Easily assembled.
- Can be taken down and stored flat when not in use.
- Very affordable.
- Protects plants from frost.
- No base required.
- Blends well into the surroundings.
Disadvantages of a clear polythene grorack greenhouse
- Lightweight so could blow away in high winds.
- Cannot be heated.
- Limited scope.
How to choose which size greenhouse you need
If possible choose a greenhouse that’s at least a size bigger than you think you’ll need because a small one will soon feel restricting.
Ensure that you can stand up and move around inside the greenhouse comfortably and choose a model that provides good access. Single sliding doors are popular but for wider access double doors might be better. The height of the door is important to – make sure you can go in and out of your greenhouse without banging your head every time.
Here are a few tips to help you choose the right size:
- Choose the site.
- Decide the best direction avoiding shade.
- Mark out the site using bamboo canes and string.
- Stand back and make sure you’ve given yourself enough surrounding space to work in and access the greenhouse easily.
Where to position your greenhouse
Position your greenhouse where it gets maximum sunlight, avoiding the shadow of adjacent buildings or trees and hedges. Overhanging trees are a hazard in themselves, especially in autumn and winter when falling leaves will block light and high winds could bring down heavy branches. Leave plenty of surrounding space for loading and unloading wheelbarrows and for lifting heavy bags of compost or pots.
Choose a sheltered spot avoiding exposed, cold windy parts of the garden or frost pockets. If possible position the door to the leeward side of the prevailing wind. Wind and frost lower the temperature so a sheltered spot will help keep heating bills down.
For convenience, build your greenhouse as close to the house as possible because it will give you easier access to mains power for heating and lighting plus a handy supply of water. If you are going to be using your greenhouse mostly during the summer, it’s an advantage to run the long axis north to south where it will benefit from maximum light. Alternatively, if you are more likely to use it during spring, then, if possible, run the long axis east to west. But with today’s modern greenhouses, particularly the aluminium framed models, the proportion of glass to frame is so high that light loss is minimal.
Aluminium greenhouse vs wood greenhouse
Greenhouse frame
Greenhouse frames are manufactured from either aluminium or wood.
Aluminium is available in a choice of colours, silver or powder coated green, green being a popular choice because it blends in so well into its surroundings.
Wood greenhouses are made from a hard wood such as red cedar. If looks are your priority and you can stretch your budget, then choose wood. To offset the initial greenhouse cost, you’ll benefit over time from lower fuel bills because wood retains heat better than aluminium.
Advantages of an aluminium framed greenhouse
- Affordable.
- Rust proof.
- Lightweight.
- Easy to assemble and erect.
- Low maintenance.
- Choice of colours, natural silver colour or powder coated green.
- Green powder coating finish is easy to keep looking good as new.
- Green blends well into its surroundings.
Disadvantages of an aluminium framed greenhouse
- The silver colour discolours with age to a dull grey.
- Winter heat loss is high unless insulated and/or heated.
Advantages of a wooden framed greenhouse
- Traditional appeal.
- Superior looks.
- Delivered in large, pre-glazed sections.
- Wood is heat retentive which helps reduce fuel costs.
Disadvantages of a wooden framed greenhouse
- High maintenance.
- Expensive.
- Heavy, so professional installation is recommended.
Greenhouse glazing and replacement glass
Three common kinds of greenhouse glazing are: standard horticultural glass, polycarbonate safety glazing and toughened safety glass.
The difference between standard horticultural glass and toughened safety glass becomes apparent if it breaks. Standard horticultural glass splinters into sharp, potentially damaging pieces whereas toughened safety glass shatters, like a car windscreen. Both are clear.
Polycarbonate safety glazing on the other hand consists of two sheets joined together so that it functions like double glazing. The polycarbonate material is shatterproof, and although lightweight it is strong. However it is opaque.
Advantages of using standard horticultural glass
- Affordable.
- Clear for superior looks.
Disadvantages of using standard horticultural glass
- Splinters when broken.
- Can be dangerous if broken.
- Occasionally breaks for no apparent reason, particularly as building ages and comes under more stress.
Advantages of using polycarbonate safety glazing
- Made up from two sheets of polycarbonate which acts like double glazing.
- Superior insulation.
- Stronger than standard horticultural glass.
- Lightweight and flexible.
- Shatter proof.
- Good light diffusion for even illumination.
Disadvantages of using polycarbonate safety glazing
- Two joined sheets encourage algae growth which is difficult to remove.
- Unstable in a high wind which could blow out the flexible glazing sheets.
- Opaque.
Advantages of toughened safety glass
- Very strong.
- Safer if broken – crumbles like a car windscreen.
- Clear for superior looks.
Disadvantages of toughened safety glass
- More expensive.
Greenhouse base and flooring options
Base
To provide strength and stability from the ground up your greenhouse must be installed onto a base perimeter plinth. A base constructed from bricks and mortar will do the job adequately. The appropriate base can also be purchased in strong galvanised stainless steel.
Flooring
Once your greenhouse is erected, you’ll need a floor. A concrete slab makes a good floor, but equally wooden decking, patio slabs, gravel, bricks or even rubber matting are all functional. Remember to provide drainage for water run-off. Make sure when you lay the floor that it won’t create a tricky doorstep and that it still leaves enough height in the roof space for you to stand up comfortably. You’ll need a hard-wearing path out of the greenhouse too and you could extend the floor outside to provide a solid, dry surface.
Assembling and installing a greenhouse
Your greenhouse must be assembled in accordance with the accompanying Instruction Manual, these are usually clear and easy to understand. No specialist tools are required, and anyone with a competent level of DIY expertise should have no difficulty, but if you have never erected a greenhouse before you may wish to enlist the help of a professional installer. See our building a greenhouse project.
Accuracy is key to building a stable, solid greenhouse. Therefore it must be installed on to a perimeter base plinth. You could construct this using bricks and mortar.
Planning permission
It is highly unlikely you’ll need planning permission but if you are in any doubt, contact your local planning office. As a matter of courtesy it is always a good idea to notify your neighbours about your plans.
Greenhouse heating
Heating
Choose a heating system to match your plants’ needs during winter. Aim for a minimum temperature (45f). If your plants are going to need higher temperatures then a mains fuelled system may be the only answer.
Advantages of using electricity to heat a greenhouse
- Convenient.
- Clean and efficient.
- High temperatures can be achieved.
- Thermostatic control.
- No fumes.
- Little condensation.
- Fan heaters deliver even heat.
- Fans can be reversed in summer to cool.
Disadvantages of using electricity to heat a greenhouse
- Professional installation by qualified electrician.
- Installation cost (especially if far from mains supply).
- High running costs especially to achieve high temperatures.
Advantages of using gas to heat a greenhouse
- Easy to install.
- High temperatures can be achieved.
Disadvantages of using gas to heat a greenhouse
- Gas bottles heavy and awkward to carry.
- Must store a full spare bottle to ensure continuous supply.
- Fumes.
- Condensation.
- High running costs especially to achieve high temperatures.
Advantages of using paraffin to heat a greenhouse
- Easy to install.
- Heaters relatively inexpensive to buy.
- Ideal for smaller greenhouses.
- High temperatures can be achieved.
Disadvantages of using paraffin to heat a greenhouse
- Needs daily maintenance – lamps filled, wicks trimmed.
- Fumes.
- Condensation.
- High running costs especially to achieve high temperatures.
Advantages to using insulating bubble-wrap
- Very affordable.
Disadvantages of using insulating bubble-wrap
- Inconvenient to install.
- Low temperatures.
- Loss of light.
- Encourages algae.
- Requires good ventilation.
- Unattractive appearance.
Greenhouse ventilation
Greenhouses are usually supplied with ventilation as standard but depending on where your greenhouse is positioned and the growing conditions you’re going to need for your plants, you may find you need additional ventilation.
Roof and side vents
There are two kinds of vents – roof vents and side (louvre) vents and in both cases you have a choice of either manual or fully automatic control.
The way these vents work is that roof vents allow hot, rising air to escape whilst the side vents draw in fresh, cooler air from lower down. It’s best to install a combination with the emphasis on roof vents.
Automatic vents are the ultimate in convenience – solar powered, once they’ve been set they just open and shut automatically and maintain an even temperature.
Greenhouse staging, shelving and accessories
To get the most from your greenhouse and extend your growing capacity you will need to install shelving. For maximum growing space you could install shelves along both sides and across the end, but you may prefer to leave one side free of shelving to grow plants from pots or gro-bags on the floor. Staging is the support structure for the shelves.
Basic maintenance
Because you are raising plants in an artificial environment, it is essential to keep your greenhouse clean so as to avoid a situation where pests and diseases will thrive and damage them.
Here are some basic steps to ensuring a healthy, disease free greenhouse.
Exterior
Aluminium – Once a year, generally in the spring, wash your aluminium framed greenhouse with warm soapy water and rinse with clean water. You may find it necessary to clean the glazing more regularly, especially if there are trees nearby. Don’t forget to clean out the gutters too.
Wood – At least once every three years the frame of your wood greenhouse will need to be thoroughly treated to prevent wood rot. Clean the glazing as and when required in the usual way, as well as cleaning out the gutters.
Interior
At least once a year, generally in the spring, remove everything from your greenhouse and scrub the walls, floor and ceiling with a garden disinfectant to remove all the debris. Rinse with clean water. Then do exactly the same to all the shelving and staging and any unused pots or trays before you replace them.