The foundation of a greenhouse is a key to a successful structure. If you don’t have a good foundation your greenhouse won’t function properly.
The problems like doors which can’t close and windows which don’t open are quite popular if the foundation is not stable.
In the worst case scenario, the whole structure can be damaged due to strong winds or bad weather conditions.
Also, I am pretty much sure that manufacturer’s warranty doesn’t cover the damage to a greenhouse caused by a poor foundation.
So, I wanted to talk about the variety of greenhouse foundation options and, hopefully, you can decide which one is suitable for you.
Prior to choosing a foundation you have to consider some very important factors.
Factors affecting the choice of a greenhouse foundation:
- Orientation and composition of the site for your greenhouse;
- Available building materials;
- The permanence of your greenhouse structure;
- And the last but not least – your budget!
Where is the best place to site a greenhouse?
I want you to assess the site you are planning to have your greenhouse. Check if the area is level or sloped.
If it is slightly sloped, you can easily resolve it. Simply build it up with more soil. The best place to site a greenhouse is on a west-facing wall of the house.
It is the most sunny location, so a greenhouse will absorb the most of the sunlight throughout the year.
Severe weather conditions can affect the ground type as well. For example, if you live in an area with harsh winters, the soil can freeze and move the whole structure.
Think about the foundation which can withstand the moving of the frozen ground.
Knowing whether you are having a permanent or a temporary greenhouse structure impacts on your decision which foundation to choose.
If you are planning to move your greenhouse in future, consider a foundation which can support the weight of the greenhouse and at the same time can be easily removed.
Okay, let’s finally move onto the greenhouse foundation options!
Option #1 – Compacted Soil or Earth based greenhouse
Depending on the ground in your area is it possible to site your greenhouse directly onto the soil.
The soil should be compact and firm. You can additionally compact soil with a roller to avoid subsidence.
Make sure that the ground is flat and level it off with a spirit level. Compacted soil foundation option is the cheapest and easiest in comparison to others.
It is suitable for greenhouse up to 8ft x 10 ft in size. Most greenhouses come with metal plinths on each corner which have anchor ‘spikes’.
These are specially designed to be splayed out and cemented into the holes in the soil to ensure that the base is not going to move.
The compacted soil foundation is a perfect option for temporarily greenhouses.
For example, portable greenhouse without a solid base can be anchored to the ground with ground stakes.
These are simply driven in the ground through the base of the greenhouse. It is easy, quick and efficient, but you can’t expect it to withstand strong winds.
The major advantage of the soil foundation is that you can use existing ground for growing. Also, it also ensures a good natural drainage.
Some of the drawbacks include:
- water logging, mud and weed growth;
- an easy access for rodents and pests;
- not suitable for larger size greenhouses.
Option #2 – Perimeter Base for greenhouse
If you are looking for more secure but cost effective option, a perimeter base might be a good option for you.
All you need to do it to build a solid perimeter to sit the greenhouse base on. You can make it out of breeze blocks, kerb-style slabs, bricks, paving slabs or concrete.
That way you leave the central floor section free and can plant directly onto ground. Also, you can gravel the central part to keep it neat and tidy or make a pathway.
This option doesn’t require as much materials as if you would fully concrete the base.
It is very important to check the sizing of your greenhouse before making a perimeter base, so it fits perfectly.
I would recommend to mark the boundaries on the ground with a spray paint. With this method you can build a foundation on the ground without digging under the ground.
Remember to fix the base of your greenhouse to the paving slabs or concrete with heavy-duty anchors and screws.
What I like about the perimeter base is that it is quite cheap to build and you can use the available building materials.
Also, it is much more stable rather than sitting your greenhouse directly on the ground. However, the main disadvantage is that is it very tricky to take the correct measurements and build the construction right.
Option #3 -Wood greenhouse base
I can say that it is the most common type of foundation for a greenhouse. The best option would be to make a pressure treated wood perimeter base.
Similarly to the perimeter base option discussed above but instead of blocks or bricks you are going to use a safely treated lumber. Naturally resistant wood like cedar is a good option as well.
How to build a base for a greenhouse?
Simply make a perimeter foundation in the dimensions of your greenhouse and most of them will come with the holes on the bottom.
Then you just need to screw right through the frame into the wood. Make sure that the wood frame is staked to the ground.
The easiest way is to drill the holes through the lumber and use two steel reinforcing bars in two foot sections and hammer it straight down into the ground.
That way you will provide a sturdy base to hold most of the smaller framed greenhouses.
This option is definitely more durable rather than sitting your greenhouse on the ground and has the same advantages are a perimeter base made of bricks or other material.
Option #4 – Paving slabs greenhouse foundation options
This is probably the most expensive and fancy way of making a foundation for a greenhouse.
However, if you are happy to keep in plants in the pods or to grow from grow bags, then the good news are that this base will function for decades.
So the principle is to assemble a base of paving slabs which are usually bigger in size or paving block which tend to be much smaller.
Which one to choose is up to you. It is also a good idea use the available building materials rather than buy new ones.
This is a good way to decorate your greenhouse which is also very practical. The base is going to look good and requires minimal maintenance.
The main advantage of this method is that it provides a greenhouse with natural drainage.
The excess water drains away easily and quickly through the gaps between the slabs or blocks. That way you can make sure that your greenhouse stays nice and tidy.
Similarly to the perimeter base you can fasten your greenhouse to a slabs/paving base with the screws and anchor for better durability during windy weather.
This base can also hold bigger greenhouses. However, you have to make sure that the slabs are bedded well and will not move and warp over the period of time.
Option #5 – Concrete Greenhouse Base
If your budget allows, a concrete foundation is the most durable and hard-standing way of securing your greenhouse to the ground.
Can I put a greenhouse on concrete?
If you already have a patio on a concrete slab, you can sit your greenhouse on it as well. However, pouring a concrete pad can be a little pricey and hard to do.
This is an ideal option for larger greenhouses, especially for the commercial ones.
Similarly to the previous option, it is quite easy to take care of. Just clean the concrete pad with broom.
Then wash it down during the regular maintenance checks to prevent the diseases. There is a low chance of rodents to tunnel inside the greenhouse as well.
Unlike the paving slabs, concrete pad doesn’t have any gaps which will let the excess water to drain through.
Standing water can lead to a mess and bad odor inside your greenhouse. So if you chosen to go for this option, think about the drainage system.
Sometimes it is enough to drill the drainage holes but I would advise to consider a more reliable drainage system like a French drain.
What is the best base for a greenhouse?
A concrete base is the best base for a greenhouse in terms of the sturdiness and durability. However, it is quite pricey and requires a drainage system.
Also, you will store the plants in pots instead of growing them from the ground.
The best foundation option is to build a perimeter base foundation using pressure-treated wood or paving slabs.
You will lift the greenhouse above the ground level and still can grow plants directly from the soil. There is no need to have a drainage system.
I hope this guide helps you to get an idea about different greenhouse foundation options.
Let me know what foundation you want to build for your greenhouse in the comments section down below!
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Happy growing 🙂