Tips for Designing a DIY Greenhouse

Plotting out a greenhouse? Here's what to consider when building it yourself.

plastic bottle greenhouse an eco friendly project
This school project used recycled bottles to build a greenhouse. Martin Leigh / Getty Images

A greenhouse can be a very useful addition to a garden–one that is well-placed and well-designed can make all the difference for your growing efforts. But greenhouses can come in many different shapes and sizes, and it can be difficult to work out which choices are right for you and your particular garden.

While you could simply choose to purchase a greenhouse off the shelf, it can often be greener to go your own route and take a DIY approach. But where should you begin? These tips for designing a DIY greenhouse may help.

Choosing Materials for a DIY Greenhouse

View of the greenhouse made of old window frames and improvised materials
A greenhouse made of old window frames and improvised materials. Berkut_34 / Getty Images

One of the first things to consider if you want to make your own greenhouse is what you will make it from. The materials you choose for your greenhouse are often one of the most important things. They can determine whether the greenhouse functions as it should, and will also play a role, ultimately, on how long your greenhouse will last and how sustainable it will be.

Glass greenhouses will typically be warmer than those covered with a plastic sheet type cover. However, they are also vulnerable to breakages, and cannot be repaired as easily. If plastic is chosen, then it is important to choose plastic which is reclaimed, not new, which will last as long as possible, and which will be recyclable at the end of its useful life.

In terms of materials, the most sustainable ones will be any from a wide range of natural and/or reclaimed supplies. From old doors and windows to plastic or glass bottles, it is great to try and exhaust all options for using natural or reclaimed materials available in your area before you resort to buying new.

Determining the Best Location

Choosing materials should go hand and hand with thinking about location. Greenhouses should always be designed with reference to a specific site. The best strategies will often be those that take advantage of the topography, natural and built environment of the site, and/or make use of site-available resources.

One example of this is building a partially earth-sheltered greenhouse into a sunny, south-facing slope (in the northern hemisphere). Another example is placing a greenhouse against a south-facing wall, (again, in the northern hemisphere) to take advantage of the thermal mass of the existing structure.

When thinking about the best location for a greenhouse, you need to think about light and shade. You also need to consider prevailing wind direction. And it is usually best to choose a relatively sheltered spot for your new DIY build.

If no sheltered spot can currently be found, don't overlook the potential for improvement to the site before you begin. You might, for example, plant a shelterbelt or windbreak hedge before you begin building.

Size and Shape Decisions

Philippe Gerber / Getty Images

Another important consideration when creating a new greenhouse is how large it should be. A greenhouse can be useful no matter how small. But generally speaking, you should make your greenhouse as large as you are able. No matter how large your greenhouse, it always seems that you'll quickly run out of space! This is especially true where winter growing is only possible undercover. The larger your greenhouse, the more food, and the more varied food, you would be able to grow year-round.

However, while trying to get as much space as possible, you should also be sure to consider practical matters. Think about whether you will really be able to heat a space of that size (when heating is required over winter). And about whether you will really have the time to tend the plants in the space.

Thinking about the shape of the greenhouse carefully can also help you avoid making costly mistakes. Consider the stability of the structure. Think about whether you will need a steeply sloping roof, to shed snow in winter, for example. Think about how the shape will determine how easily you can work inside, and which plants you will be able to grow there. For example, if creating a tunnel shape, it can be better to have vertical sides before the arch over the top, as this makes it easier to tend and grow right to the very edges of the space.

Consider the Practical Necessities

It is surprising how often simple practical necessities are forgotten when people build their own greenhouse structures. But when you are caught up in a project, it can be easy to overlook the basics. Here are some ideas to help you avoid some common pitfalls:

  • Plan irrigation from the outset. Think about how you will water plants grown undercover.
  • Think about ventilation, and how you can increase airflow. A greenhouse can get very hot, even in cooler climates, through the summer months. Doors should open at both ends, ideally, to create a through breeze. And roof vents and side vents may also be useful.
  • Plan for winter from the outset too. Think about winter heating (if required), and build to incorporate thermal mass into the structure to keep temperatures more even throughout the year and the interior frost-free during the coldest months.
  • Think about how the structure itself can also double as support for vertical growing. Internal posts, cross-brace bars, etc. can be useful for maximizing production if they are in the right places.
  • Consider access. Make sure pathways are wide enough for easy access while growing space is maximized. Make sure it is easy to get around and easy to move items to and fro in and around your DIY greenhouse.

There is of course more to think about, but considering all of the above should set you out on the right track as you begin to plan your undercover growing area.