Choosing Your Greenhouse

Choosing your greenhouse involves considering a range of factors, some of which we looked at in a previous blog, Planning Your Perfect Greenhouse. This time, I’d like to go into detail on choosing the best site for your greenhouse and which style and material might best suit your desires and budget.

You’ve probably looked online at some of the many greenhouses that are available, and, if you’re anything like me, got suitably side tracked into imagining the different types of glasshouse you’d have in the garden – one for propagation and overwintering plants (optional heating), a decorative one for the display of tender plants (definitely need to be heated) another for alpines. Plus a few cold frames to help with hardening off. If only your garden and budget were large enough…

I think we should head back to reality and consider the salient points to help you to make the best decision.

How much space is available in your garden?

I suggest you start by considering whether the popular 8’ x 6’ sized greenhouse will fit. Unless you have a really small garden, in which case perhaps take a 6’ x 4’ size. It’s easy enough to scale sizes up or down and remember that whilst an 8’ x 6’ may not fit, a 7’ x 5’ might.

In other words aim for as large a greenhouse as you can fit in – you’ll use it and still need more room!

If space is tight for a freestanding greenhouse, could you have lean-to version against the house or a garden wall? There are benefits to this. For example, an unheated greenhouse against the house is likely to be warmer overwinter than a freestanding one.

When you really want a 12’ x 10’ greenhouse but can’t fit it in anywhere, consider whether a combination of smaller greenhouse and separate cold frames would work. Also depending on the plants you’ll be growing, would two smaller greenhouses meet your needs and fit in the space available? They don’t have to be side by side.

small plastic greenhouse with staging & plants

Choosing the best site for your greenhouse

Hopefully, you have a choice of two or three places where a greenhouse will fit. Next, decide whether you’d like it to be near the kitchen door, generally ‘on show’ but not right next to the house, or hidden away (allowing you to ‘escape’).

And now down to the nitty gritty of what the greenhouse needs to be a successful partner in your gardening life.

Aspect and sunlight

Possible issues –

Constant bright or full sunlight
Overhanging trees
Exposed, windy sites

Sunlight

Traditionally, greenhouses in the northern hemisphere were positioned so that the ridge-line of the roof followed an east to west axis. The idea of this was to ensure that the longest side of the greenhouse would be fully exposed to the sun from the south.

Now this is still a good idea if you are planning to have a long greenhouse, but for smaller greenhouses which, when you look at the dimensions, are more square, it is less important. For example, the popular sized 6’ x 8’ greenhouse is more square than rectangular when compared to a 10’ x 20’ greenhouse.

For the smaller, squarer type of greenhouse, a south or southwest facing aspect for any one of the sides will give you the good exposure to sunlight.

However, if this isn’t possible because of where you have to place the greenhouse, so long as the roof catches direct sunlight, this should be sufficient to warm it up with free solar energy.

Overhanging trees

Overhanging trees and tall hedges will cast shade. This could be useful if they protect your greenhouse from the hottest part of a summer’s day by shading it.
If they’re on the ‘cold side’ they may offer some frost protection during winter.
Are they a windbreak? On exposed sites, shelter from strong winds is beneficial.
However, overhanging trees can also pose a possible damage threat as they may fall onto your greenhouse. It is generally advisable to prune branches before building your greenhouse to avoid this issue.

Exposed, windy sites

Not a perfect place for structure predominantly made from glass! All greenhouses are vulnerable to strong winds. However, sometimes, you have little choice if you live in a hill or near the coast. If you don’t have a convenient hedge, consider adding an alternative form of shelter. For example, trellis fencing, with or without climbing plants is one option, especially where space is too limited for a hedge.

Tips for Planting a Coastal Garden blog banner, marie shallcross, plews potting shed, gardening writer

Level site and base

A level site is essential or your greenhouse frame may twist out of shape and be less stable. It also makes creating the base a lot easier.

The foundations or base for your greenhouse will vary slightly depending on the size and type of greenhouse that you’re planning to have. Be sure to check the manufacturer’s instructions.

You will, at the very least, need concrete footings to support the base of larger greenhouse frames or if you are having a greenhouse with a dwarf wall. Is it too obvious to state that these footings and wall will need to be exactly the same size as the frame?

NB The base for greenhouses is usually six inches wider all round than the dimensions given for the frame.

Although some greenhouses have a solid concrete floor, this is not always ideal as it can create drainage issues. Watering plants and condensation will lead to puddles on the floor. However, if, when laying the concrete base, you add drainage channels and slope the floor towards them it shouldn’t be an issue.

Alternatives to a solid concrete floor are –

Flag stones (paving slabs) laid on compacted sand. This allows for the floor to be easily swept and water can soak away through the gaps between the paving slabs.
Gravel contained within a concrete fillet. The fillet will also support the frame of the greenhouse. The gravel can be spread between a mesh network to keep it in place. It can be a pain to sweep clean of soil.
Stripped footing – where you want to grow plants in the ground but inside. There is a flag path in the middle of the floor and a shallow bed on one or both sides. In large greenhouses there is often a raised bed or staging down the middle, with a path on each side (ie running between this and the staging or beds against the wall).

wooden greenhouse being built, original photo by rosshelen from rosshelen

polycarbonate greenhouse, raised beds, original photo by elisabeth coelfren

Will you need an electricity supply?

You’d be surprised (or maybe not) at how many gadgets there are available for greenhouses that require electricity. For example, heaters, lighting, grow lamps, propagators and automatic watering systems.

However, most, if not all of these accessories can be powered in other ways. For example, battery operated lights and propagators, capillary action watering systems. The latter two are of course available as ‘non-powered’ options.

Whilst you may not want all of these, if you think on balance that you will use an electricity supply, then organise it in the planning stages. And get a qualified electrician to do the work – water and elecrticity don’t mix and neither do secateurs, spades and unprotected wires!

Water Supply

You will definitely need access to water! Options include –

Water butt catching rainwater from the roof of your greenhouse.
Water tank if internal can help regulate the temperature.
Outside tap – consider how you will route water pipes from existing supply to greenhouse.
Automatic watering system will need a water supply, whether mains or tank, which also means pipes and electricity.

Simplest is usually best; but do plan ahead for the more expensive options as its generally more cost effective to fit at the beginning rather than later – especially if it means taking up floors!

Exterior Maintenance

Measure those possible spaces – you will need to allow about 1 metre of space all around the greenhouse in order to clean the glass, scrub down the frame, apply more preservative if a wooden greenhouse.

Visual appearance of the greenhouse

You’ve worked out options for where greenhouse will fit, allowing for sun, wind, etc. But when choosing your greenhouse how critical is the style?

Considerations –

personal choice of materials and style
your budget
where in the garden the greenhouse will be placed

Materials and styles of greenhouse.

Styles

Rectangular greenhouses, these may have –
- Apex roof, low eaves,
- Apex roof, high eaves
- Curved roof
Octagonal greenhouse
Corner greenhouse
Lean-to greenhouse

Frame

Metal – basic aluminium or coloured
Wood – soft wood or hardwood

Glazing

Safety glass
Horticultural glass
Styrene (clear)
Polycarbonate
Plastic / pvc

brick half wall & timber greenhouse, original photo Annie spratt on unsplash

octagonal greenhouse, arch, trellis, vegetable area with raised beds and wooden greenhouse, grow your own

Other things to consider when choosing your greenhouse

When you’ve seen a style that you like at a good price, do check what is included as standard. Some of the ‘optional extras’ are actually necessary!

Door height – some of the more economically priced greenhouses have low doorways, 5’ 2” is not uncommon
Staging and shelving – this can be fixed to the frame or freestanding, or a combination
Opening windows and vents – essential for temperature control. In my opinion, automatic roof vents are worth the extra cost
Do you need a low or no doorsill? The frame and base of the greenhouse generally go across the doorway, creating a step and making a potential trip hazard. A ramp can be built over this for wheelchair access or there are ‘sill-less’ models

Delivery times – vary from 3 days to 10 weeks. Allow yourself time to prepare the site.

Most smaller greenhouses can be put up over a weekend by two competent DIYers. Larger ones are best erected by those who do it regularly.

And if the greenhouse you really want means saving up some more money, you could always buy a coldframe first. You’ll find the extra covered planting space will be useful even when you have your greenhouse proper.

dwarf brick wall for greenhouse, gravel and mesh floor

and finally

Hopefully, this choosing your greenhouse blog has answered most of your questions, but if you need more help, please do get in touch. By the way, a greenhouse would make a stunning birthday, Christmas, anniversary or Mother’s Day present! And the source of other gardening gift potentials, for example, greenhouse staging, potting bench, seed trays.

And if you’d like a gardening course on using your greenhouse to the full, learning more about your garden and gardening, why not ask about our bespoke Gardening Lessons, where your classroom is actually your own garden. We can help you learn gardening basics, carry out worm and other experiments and also show you how to plan an ornamental border or kitchen garden.

For further gardening advice and inspiration, check out Plews Potting Shed blogs, including the selection below. You could come and find us on Instagram Pinterest and Facebook too.

Feeling nosey? You can have a peek at the progress of my garden renovation, Spitfires and Slow Worms, on Instagram and Facebook

You’ll get to see it in person if you come to the Plews Gardening Workshops Current ones on Eventbrite for you to book into. Follow for updates on topics and dates on Plews website, Instagram, Eventbrite, Facebook

Plus get your local garden club, allotment, WI, U3A or other group to ask me along to give a talk(and bring plants 😉)