How To Choose A Greenhouse

Buying a greenhouse will extend your gardening horizons, allowing you to grow a much greater variety of plants throughout the year. Here, Andy Taylor answers some of the questions he is frequently asked.

Created by Andrew Taylor on Wednesday, 19th of August, 2015.
Updated on Thursday, 9th of February, 2017.


There's such a large range of greenhouses the choice can be bewildering. Our customers already know how much they have in their budget and how much space there is available in their garden, but need guidance on many other deciding factors. We are always happy to oblige, advising on a raft of considerations including:  

What's Better, Wood or Aluminium? 

Wood pros and cons are:

  • A traditional feel, can be easier on the eye and blends into the garden
  • Insulates better and is therefore cheaper to heat than aluminium
  • Heavy, you may need help to assemble
  • Pressure Treated, Dip Treated timber and ThermoWood® are very rot resistant 
  • Cedar will last for many years with the minimum of attention

Aluminium pros and cons are:

  • Easy to assemble
  • More affordable than wood
  • Lighter and stronger than wood
  • Tends to let in more light
  • Coloured metal will allow greenhouse to better 'blend-in'
  • 'Silver' will discolour to grey
  • Corrosion can be avoided by buying painted, anodised or powder coated metal
  • Condensation on the frame can be a problem
  • Poor insulator and is therefore more expensive to heat

What's The Best Style?

Traditional freestanding

These let light in from all sides, there's plenty of room for staging and they are very practical. This style offers the most growing area. Modern styling has seen elegantly curved glazing introduced and a 'barn' style offers extra height for tall plants. 'Orangery' type constructions are as much about outside leisure as gardening.

Free standing circular or lantern shaped

These are attractive designs but space is limited. They are most suited to the smaller garden.

Conservatory or lean-to

Good if you have restricted space but unsuitable for north facing walls and can overheat if south facing. Light levels are reduced and traditionally the back wall has been painted white to return any available light to the plants. The back wall retains heat and can also be used to train and support climbing plants. If there is an internal door, lean-tos are very convenient as essentially you don't need to leave the house but, like any conservatory, they can become very hot during the summer.

Wall Garden

Fixed against a wall with a series of shelves, attractively styled these are perfect when space is at a premium.

Is A Bigger Greenhouse Better?

Whatever the style, the general rule is to go for the biggest you can afford and can accommodate. From 4ft x 6ft to the cavernous 20ft x 10ft, your greenhouse will soon be full to capacity. Think about how much use it will get, what types of plants are to be grown, how much storage is required, also consider aesthetics and whether or not you want the greenhouse to dominate your garden.

What's The Best Position For My Greenhouse?

Do not position the greenhouse:

  • Where it will fall into shadow of, for example, a building
  • Under trees (falling leaves will block light and fallen branches will damage the greenhouse)
  • In a frost pocket or exposed to cold winds

Do position it:

  • On a firm well drained site that is easily accessible
  • In the sunniest part of the garden with the longest side facing south (although with smaller greenhouses, that are practically square, this isn't important)
  • In sheltered position away from high winds, making sure the door is facing away from the prevailing wind
  • If it is a 'lean-to' style, always locate on a south facing wall
  • As near as possible to sources of water and electricity (always have a store of water in the greenhouse so you use it at the ambient temperature)

Does The Greenhouse Need A Base?

A pre-formed base is not essential, after obtaining the base dimensions you can construct one. However metal bases come as standard with many greenhouses or can be bought to save you a lot of time and trouble. Any base should be securely attached to a foundation, definitely not soil or turf, this may be slabs or concrete, overlapping the edge of the greenhouse by about 6 inches. 

To lay the strongest foundations, you can excavate the ground around the perimeter of the greenhouse to create a strong foundation. Dig out a spades width to a depth of 5-6" around the edge. Fill the bottom 3-4" with rubble, hardcore, stones etc. and crush it in. Either add 2-3" of concrete mix on top, if you want concrete, or add a few more smaller stones, firm down & top with 1" sand, on to which you can lay slabs (maybe 18" x 9"). Alternatively fill all the hole with hardcore, crush in firmly and top with a sprinkling of sand to level it off. 

What Type Of Flooring Should I Install?

Concrete slabs are ideal but at the same level as the entrance door or else they'll be a dangerous little step. Also think about wooden decking, bricks or gravel.

What Are The Different Types Of Glazing?

Greenhouses normally come with two or three glazing options:

Standard Horticultural Glass

  • Cheapest option
  • Clearest glass for maximum light
  • Splinters into shards and can therefore be dangerous
  • Breaks easily under slight pressure eg when cleaning or fitting

Toughened Safety Glass

  • Much stronger than standard
  • Disintegrates rather than breaking into shards
  • Clear glass

Polycarbonate

  • Expensive
  • Similar to double glazing, offers better insulation
  • Harder to break than standard glass
  • Transmits 85% of light with good diffusion
  • Cavity between glazing can attract condensation and algae
  • Lets in less light
  • More vulnerable to wind damage

Does The Greenhouse Need Staging?

It is really useful to have staging along least one side of the greenhouse, offering space to perform a number of tasks and also on which you can place plants and seedlings nearer the light. Pots and other equipment may be stored underneath.

Is There Sufficient Ventilation?

You must control the temperature in a greenhouse and during the summer this is achieved mainly through ventilation. Always check that there is sufficient ventilation at all levels as, during hot weather louvres near ground level are used to allow in cool air that will then heat up and rise, exiting through top ventilators, thus providing an effective throughput of air. Check out the different types of manual and automatic ventilators that open and close according to temperature.

Do I Need To Invest In Heating?

Heating will be a deciding factor on the variety of plants you are able to grow and the number of plants that can be kept over winter. Temperature during the winter shouldn't dip much below 10C and throughout the year the daily variation shouldn't be more than 10C, this can be controlled by a combination of heating, ventilation and insulation. The main types of heating used in a domestic greenhouse are:

Electricity

  • Easy to use, reliable
  • Clean, no odour or fumes
  • High temperatures can be achieved
  • Temperature can be controlled by accurately and cost effectively with a thermostat
  • Fan heaters provide uniform heat and good circulation
  • Fans can also be used to cool in warmer months
  • Professional installation is required to install waterproof cables and sockets

Gas

  • Propane and butane are easy to use
  • High temperatures can be achieved
  • Temperature can be controlled by a thermostat
  • A spare cylinder must always be available
  • May give off harmful fumes
  • Causes condensation

Paraffin

  • Cheap to buy but running costs may be high
  • Temperature control is difficult
  • May give off harmful fumes
  • Requires frequent re-fuelling and daily maintenance
  • Creates humidity and condensation

Solar energy or wind turbines may become a consideration in the future but at the moment they are far too expensive due in part to the poor heat retention qualities of a greenhouse. Spent cooking oil is used occasionally commercially but is messy, smelly and not really suited to small scale production.

What Are The Other Optional Extras?

  • Insulating bubble wrap 
  • Capillary matting for watering
  • Blinds
  • Shading (a proprietary mixture that is applied to the glass to protect plants from direct sunlight)
  • Water tank (to warm water to the ambient temperature)
  • Min / Max thermometer to ensure temperature is accurately measured and can be controlled
  • Rainwater collection kit

Can anyone erect a greenhouse?

Yes, two people are generally better than one and you may find this blog concerning erecting a greenhouse helpful. 

Do GardenSite erect greenhouses?

We can quote to erect greenhouses bought from us. However we do not have national coverage, so please ask first, Telephone 0121 355 7701.

Why should I buy from GardenSite?

We offer a 12 month guarantee on all the aluminium structure, we also have a full after sales support system that will resolve any problems. Furthermore we have been selling greenhouses for 50 years and have two show sites, each displaying a selection of greenhouses. We are not an internet only company that simply buys and sells, with little or no knowledge. We sell with confidence so you can buy with confidence.

How are greenhouses delivered?

We use a specialist company that will telephone prior to arrange delivery. You can not send glass on a standard parcel carrier. The unit will be delivered to your door. The glass is pre-packed and then shrink wrapped into manageable packs, please lift with caution and use gloves. The unit is packed separately, and the base is packed separately.

If you need advice on buying a greenhouse, don't hesitate to contact our sales team on 0121 355 7701.

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