How to secure your greenhouse

Wind resistance

Unsurprisingly, the main danger facing your greenhouse or polytunnel is the wind, which can weaken the cover of your structure. More seriously, however, strong gusts may enter the greenhouse via the air vents and can even uproot the structure from the ground. Even light winds can undermine or cause damage to your structure.

Generally speaking, there is only one reliable solution to prevent this: choosing a solid fixing system suitable for the size of your greenhouse. It goes without saying that a greenhouse designed to hold four tomato plants won't require the same precautions as one used on a semi-professional basis. Nonetheless, it is always advisable to ensure your structure is well secured in order to avoid any breakage.

Trenching your greenhouse cover 

Some greenhouse and polytunnel manufacturers provide greenhouse covers with extra material designed to be buried in trenches measuring around 20 cm in depth. Of course, this will largely reduce the effects of the wind but should only be used as an additional solution alongside properly securing your structure. You should also bear in mind that this method will only really work for small greenhouses or those installed in spots that already provide some wind protection.

Securing a greenhouse with pegs or ground anchor stakes

Many low-end greenhouses come with fixing pegs or stakes. Pegs can be used to hold down very small greenhouses or low polytunnel-style structures. If you feel it necessary, do not hesitate to use a sturdier ground anchor stake.

So far, we have seen a couple of options for securing greenhouses: using pegs or burying part of the greenhouse cover. However, these methods are not ideal and will not be effective if you are planning on building a large greenhouse in an area with little wind cover. In these cases, the best option is to anchor the structure to the ground using plates. These fixing plates are spread out around the edges of your greenhouse to provide strength and resistance – especially against the wind.

Ground anchor plates

Ideal for very large greenhouses, ground anchor plates mean you won't require the use of concrete slabs or another type of foundation. These rectangular plates are buried underground and are held down by the weight of the soil. Designed to prevent your greenhouse from becoming uprooted, they are generally used on soft ground.

Base plates 

Base plates can be secured into both soft and hard ground. They consist of a anchor plate equipped with two fixing pins for greater strength. The ground tubes are driven into the ground and the base plate is fixed at the surface. This fixing type is only suitable for medium-sized greenhouses.

Base plates on concrete

Base plates can also be used to secure greenhouses to concrete footings or foundations at the surface. The base is held down by fixing plugs or stud bolts.

Soft ground

Using a frame base

Using a frame base for your greenhouse is an effective way to ensure a secure hold. Of course, models equipped with bases are slightly more expensive – but they are also much easier to install!

These bases are assembled and embedded into the ground. Usually made of aluminium, they are designed to hold the frame of your greenhouse. In order to secure the structure, you will have to try your hand at mixing concrete. Start by placing the feet where you want them to go on the ground and dig a hole for each one. Your holes should be at least 60 cm deep in order to avoid frost. Insert PVC pipes with a diameter of 10 to 15 cm into these holes.

After checking that your holes correspond perfectly to the placement of the feet of the base – making sure to measure the diagonals to make sure they are straight – you can prepare your mortar. Pour it into the pipes, leave it to try and secure the base into position. This should be a quick, efficient and easy process. According to the fixing requirements of your greenhouse, you may also incorporate your plates or anchors into the mortar.

Once your foundation is fully dry, all that remains to do is to assemble your greenhouse.

Anchoring a greenhouse without a base

If your greenhouse model did not come equipped with a base, you will have to anchor the feet of your greenhouse directly into the ground. Different manufacturers will offer different methods of accomplishing this, but it's best to trust your judgment and to try to select a model that will offer strength and durability:

• Ground anchor plates are ideal for large greenhouses. It is also possible to seal these using concrete;

• Base plates are used for small to medium-sized greenhouses. Pins are used with these anchors to ensure a better hold in the ground.

Securing a greenhouse on hard ground

Securing your greenhouse into hard ground is the best way to guarantee that it will remain sturdy over time. You can take advantage of the hard ground to properly secure your greenhouse either with or without a base. All you have to do is fix the base of the greenhouse to the ground using anchor bolts or fixing plugs with a diameter of at least 8 mm.

Quick tip: if your greenhouse does not have any anchor points for hard ground, get yourself some galvanised bolt-down post supports which should ideally feature a fixing plate.

Spread these along the length and width of your greenhouse (approximately three on each side) and then insert the frame of your greenhouse. To secure the frame, use a threaded rod and bolt on each side of the post supports.

1. Surround the perimeter of your greenhouse with buried blocks and fix the structure over several points.

2. Screw anchors can be used to anchor the greenhouse to certain ground surfaces. The diameter and length of the anchor will vary depending on the size of the greenhouse and the type of ground.

3. Arrowhead ground anchors can be used if the ground is hard. These harpoon-shaped anchors can be embedded into the ground using a hammer drill.

4. Stainless steel cables can be used to link different anchors for better resistance to uprooting.

5. Set up concrete slabs or a foundation and secure the greenhouse with stud bolts, base plates or using an H-type post anchor. 

6. Take sharpened round stakes coated with tar and drive them into the ground to form different anchoring points. For a more environmentally friendly solution, use stakes made from acacia wood (the most rotproof wood available) without any type of coating. You can then use coach screws to secure the plates.

To get the best out of your garden, follow the links below for related advice from our editors and more helpful guides:

• Greenhouse buying guide

• How to design and furnish your garden

• Building tools buying guide

• Garden furniture buying guide

• Garden dining set buying guide