What Size Greenhouse Should You Choose?

It’s said that size is everything but is that true with a greenhouse? Well, yes it is, although that doesn’t necessarily mean that bigger is better. It means that getting the right size for you, your garden and your gardening interests is very important, whether you end up with something small, medium or large.

What are the options?

Let’s take a look at what’s on offer to begin with.

  • Small, cheap greenhouses, often little more than a large shelving unit covered in glass or clear plastic.
  • Small but ‘proper’ greenhouses, ones you can walk into, sometimes round but usually classically shaped.
  • Medium sized greenhouses, usually up to around eight feet long
  • Large, almost commercial-sized growing greenhouses

Of course there’s a huge amount of overlap between these somewhat arbitrary categories and manufacturers are filling the gaps all the time. The upshot is that there’s a bewildering choice of shapes, sizes and materials.

Which material and glazing?

There’s a number of articles on this site that help you to decide on the type of greenhouse and the materials used, touching on the benefits of a wooden or aluminium frame, and discussing whether to go for glass or plastic glazing. Then there are also specific articles on the very small greenhouse options and larger erections like polytunnels.

So for the purposes of this article we are going to assume that you are looking at a traditionally shaped A-framed greenhouse and need to decide between small, medium or large. We’re going to avoid discussing the frame type, whether it’s wood or aluminium, or whether it’s glazed with plastic or glass, we’ll just look purely at the pros and cons of choosing a certain size and the factors that affect that choice.

So having said that bigger is not always better, assuming you have the space, what’s to stop you putting the most humungous greenhouse you can fit in your garden?

The factors you have to consider are:

  • The way you will use the greenhouse (we’ll leave this one till last)
  • Price of the greenhouse.
  • Running costs.
  • Available space in your garden.
  • Position of the greenhouse.

Greenhouse prices

You probably already know this, but size is the major factor that determines the price of a greenhouse. Although the materials and quality make a difference too, it’s size that matters most.

If you go to the end of your budget you won’t be able to put decent shelves in, maybe skimp on the heater, that sort of thing. So don’t stretch yourself too far.

Running costs

Even in a UK summer you’re more likely to be worrying about keeping the greenhouse cool than hot. But come the winter it’s a different story. Although there’s the heating effect of the sun’s rays through the glass (even on cloudy days that still has an effect, albeit smaller) glass or clear plastic simply are not good insulators.

That means that as soon as the sun goes down all the heat built up during the day evaporates. The only way to keep frost away and not kill off all those seedlings is to run a heater, either electric or LPG, and of course the bigger the greenhouse, the more that will cost.

Available space

Of course if you have a postage-sized garden you won’t be able to fit a monster-sized greenhouse. But it’s not just the available space for the base, you also need to think about getting the materials in and out, the concrete mixer and other tools needed to build the thing in the first place.

Then think about leaving space to get yourself and your tools in and out of the greenhouse door. And then you probably don’t want the greenhouse to dominate the whole garden, so make sure it’s in proportion with the garden itself.

This leads to the positioning. If you have a sheltered spot you might be able to keep the greenhouse warmer for less, but if you make it slightly too big and one end pokes out into the bitter freezing winds, then the whole greenhouse will get colder faster, costing you more in fuel bills. Alternatively on a south facing spot, sheltered from the wind, you could go bigger.

How you use your greenhouse

At the back of your mind you will have thought about this all the time, otherwise you wouldn’t be interested in getting a greenhouse. Having the space to do everything you want is great, but heating loads of empty space because you haven’t used all of it is a waste of money.

Or the greenhouse becomes a dumping ground for all the things you haven’t got anywhere else to store, in which case you might just as well bought a shed!

So take a step back and look at what’s really going to fit. Plan it out on the ground and maybe put something like cardboard boxes down at the corners and move them around. This will show you where each size of greenhouse will actually reach and will give you a better idea.

Then check your budget, go on a tour of the garden centres and DIY stores to see what’s within your budget, then make your decision.