How to build a DIY greenhouse

Protect your plants in the garden, in the vegetable patch and on the balcony

Inspirations / How to


Estimated reading time 6 minutes

It’s a fact of life: most plants suffer from the cold. If you have a garden, a vegetable patch or just a few plant pots on your balcony, you’ll know that protecting your plants in winter requires you to adopt a series of countermeasures.

Trees and shrubs planted in the ground should be protected with a mulch at the base and wrapped with plastic or non-woven fabric sheeting. Sheeting is also a must for repairing the foliage of potted plants that, for various reasons, you cannot move indoors. Mulch and non-woven fabric are also an excellent solution in the vegetable patch to protect your winter vegetables.

However, there is also another solution that works for both potted plants and vegetable patches: build a greenhouse. In this article we explain how to build a DIY balcony greenhouse and a polytunnel greenhouse for the vegetable patch.

Designing a DIY greenhouse

A greenhouse is a protected environment where plants can live, even in autumn and winter, without suffering damage due to frost. Low temperatures are especially problematic for tender plants—meaning those that cannot tolerate temperatures below 15°C—and, in general, species grown outside their optimal climate range.

When people talk about the "greenhouse effect" affecting our planet, they are referring to the natural phenomenon that leads to global warming by exactly replicating what happens to a greenhouse containing plants. In the latter case, the sun’s rays pass through the greenhouse’s transparent covering, but the infrared rays emitted by what they heat are unable to escape. In addition, there are no convection currents in the greenhouse that mix warm and cold air. The result is that the greenhouse stores heat and its internal temperature rises.

Before building your greenhouse, decide whether you want it to have a house or tunnel structure and then choose what to build it with. You can make it with different materials, including recycled materials: the most important thing is that it has a robust load-bearing structure capable of withstanding temporary overloads—for example in the event of snow—and wind, which can be a major problem for greenhouses. The greenhouse also needs to have a transparent covering that lets sunlight through while retaining heat. One solution is commonly available polyethylene sheeting of sufficient thickness to trap heat and withstand wind and snow (at least 0.15-0.20 mm).

The dimensions of the greenhouse depend on the space available—especially when it’s limited, such as on a balcony—and/or the size of the area that you want to protect, for example in the case of a polytunnel covering the part of your vegetable patch set aside for winter vegetables.

Whether you place it in the garden or on the balcony, you can build the greenhouse against the south-facing wall of your home: in this location it will get maximum exposure to sunlight, protection from cold winds and greater thermal insulation. If, on the other hand, you build the greenhouse away from existing buildings, choose a spot in your garden that is sunny and free from trees, hedges or anything else that creates shade. Orient the greenhouse so as to minimise resistance (i.e. surface area) to prevailing winds in your area: this means lining up the long sides parallel to the wind direction.

A greenhouse should be convenient to assemble and disassemble, according to the season and your requirements: to easily transport everything you need you can use a wheelbarrow or—even better—a transporter, like the compact transporters and professional transporters supplied by Efco.

How to build a DIY greenhouse

For your balcony plants, you can buy a ready-to-assemble balcony greenhouse or instead opt for a DIY balcony greenhouse that you build from scratch, buying what you need from a builders’ yard or home improvement store, or using recycled materials. For example, you can repurpose a pallet into wooden planks and battens to build your greenhouse with. To cut up the pallet you can use an electric chainsaw—ideal for DIY projects—such as the Efco MT 2000 E with 2 kW power rating.

Now let's find out how you can make a DIY wooden unheated greenhouse (i.e. that doesn’t have its own heating system), where you can protect the plants on your balcony. In this case, the greenhouse has a house structure: in practice, it’s rather like a wardrobe wrapped in transparent film. Here is what you need to build a very simple DIY balcony greenhouse out of wood:

  • Wooden battens for the uprights and cross-beams of the supporting structure.

  • Wooden planks for the shelves.

  • Screws to assemble the structural elements and shelves.

  • Polyethylene sheeting for covering the greenhouse.

  • Pins to fix the polyethylene to the wooden supporting structure.

  • Hinges for attaching the front doors to the structure and, optionally, for the roof pitches if you want them to be openable.

We mentioned making use of recycled materials. Instead of building the DIY balcony greenhouse from scratch, for the supporting structure you can use an old wooden or metal shelf frame and cover it with polyethylene sheets or twin wall polycarbonate panels, which are also transparent.

Instead of taking up space on your balcony, you can make a DIY wooden greenhouse for your garden. Just build a larger house-style greenhouse with wooden planks instead of battens, for example using whole planks cut from a pallet.

At the beginning of the article we mentioned systems for frostproofing ground-planted and potted plants in your garden or on your balcony. You can find all the details in our article on how to protect plants from the cold.

How to build a polytunnel greenhouse for your vegetable patch

A greenhouse for the vegetable patch is not only needed to protect vegetables from the winter cold, as well as early and late frosts in autumn and spring respectively. With a greenhouse you can also extend the harvesting period of summer/autumn crops, produce certain spring/summer vegetables in advance and create a seedbed.

In the case of polytunnel greenhouses for the vegetable patch, the supporting structure consists of hoops—you can use metal rods 1 cm in diameter—while for the cover you will need polyethylene sheeting of adequate thickness:

  • Plant the hoops of the supporting structure in the ground so that they are all the same height.

  • You can first prepare the ground by making holes: space the hoops 60 cm apart if the polytunnel is quite high (1.2-1.3 m), or even further apart (80-100 cm or more) for a smaller tunnel.

  • Give stability to the structure by stretching a length of rope lengthwise over the hoops, from one end of the greenhouse to the other, and securing it to the ground with tent pegs.

  • Close the front and back of the greenhouse and cover the entire structure with polyethylene sheeting.

  • Secure the sheets to the hoops with suitable clips.

  • Secure the polyethylene covering by burying it or trapping it under weights (such as bricks) placed along the perimeter of the greenhouse.

Building a polytunnel greenhouse for the vegetable patch is not the only thing you can do to help your winter vegetables overcome the cold: read all our tips for keeping your vegetable patch healthy in winter. You will also find suggestions on species and varieties of cold-tolerant vegetables and how to manage the crops growing inside your polytunnel. Once the greenhouse is built, your work doesn’t stop there: next you need to scarify the soil, calibrate your irrigation and fertilisation system, weed the soil and so on.

When doing gardening and DIY jobs it is essential to work safely and comfortably. That is why we recommend always wearing utility gloves and suitable clothing, for example the new Efco universal light work jacket: made with breathable, rainproof and windproof technical fabric, it is ideal for working outdoors in any season.

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