Deciding on whether you need a greenhouse foundation is a crucial step in choosing a greenhouse. Choice of frame material and greenhouse glazing indicates if you need a foundation or not. And if yes, what foundation would be the best in terms of durability and maintenance.
If you just want to purchase a mini walk-in greenhouse or a portable one, then the foundation is not needed. All you need to do is to secure the plastic to the ground to keep the structure from blowing away. Needless to say that if you are purchasing a semi-professional or large greenhouse structure, it requires a sturdy foundation.
However, for a hobby greenhouse a permanent foundation might not be necessary. That is why many growers are questioning the need of foundation. To help you make up your mind we are going to discuss the pros and cons of greenhouse foundation.
What are the pros and cons of greenhouse foundation?
The main advantage of greenhouse foundation is that it lets the structure to function properly. The greenhouse consists of metal or wooden frame and glazing can be plastic or glass which makes it quite heavy. For example, a small greenhouse weights about 225 lbs.
The larger models can weight from 320 to 375 lbs. To stay level and functional a greenhouse structure needs a good support system. The most common greenhouse foundation options are brick or wood perimeter base, paving slabs and concrete base.
The pros of building a greenhouse foundation:
1. Brick perimeter base is cost-effective and easy to replace
Perimeter base offers a sturdy foundation and lets you save money on materials and time when building it. You can build brick perimeter base above ground level, so you can avoid digging out. Also, if some bricks are going to crack, you can easily replace them.
2. Lumber perimeter base is inexpensive and easy to construct
It is an ideal option for a greenhouse that is not too big. You don’t need to hire contractors to build a wooden base. Also, you can save on the materials. All you need is it to get pressure treated lumber or naturally rot resistant wood like cedar.
3. Paving slabs foundation is durable and extremely practical
If you are looking for a decorative base option for greenhouse, laying pavings slabs is the one to consider. Apart from looking good, it is easy to maintain and will last for many years. Due to the gaps between the slabs water will drain away quickly and the structure will remain dry.
It is very easy to clean – just sweep it with broom and give it a wash once a year. Use warm water with mild detergent to disinfect the base. This foundation will not move over time. Also, it is great for wind resistance. If set up correctly, you won’t have problems with broken glass panels or polycarbonate popping out from frame.
4. Concrete foundation lasts a long time and is very easy to maintain
Concrete foundation is ideal for bigger greenhouse structures. You can set it above ground level and it will last a long time withstanding nature elements. In addition, with a concrete foundation it is easy to keep the whole greenhouse structure clean and tidy.
Sweep it with the broom regularly and give it an annual wash in fall or spring. Just wash the base down with warm water and mild detergent. It will keep the structure pests and diseases free. Moreover, rodents that fancy tomato fruits won’t be able to tunnel inside the greenhouse from the ground.
The cons of building a greenhouse foundation:
Most of the time the cons of building greenhouse foundation are intensive labor and high costs. Hiring a contractor and buying raw materials can cost up to a thousand dollars. However, if you are going to a job on your own, it can often be time consuming.
Also, if you mess up with site preparation the whole structure can collapse over time. Let’s discuss the disadvantages of each foundation option.
1. The initial costs of brick foundation are quite high
Buying a bunch of bricks can be more expensive than getting lumber or raw materials for concrete foundation. Also, you will need to use mortar to secure them which adds to the labor and costs. Moreover, you need to prepare site for laying bricks, so it should be properly smoothed and leveled.
2. It is hard to keep perimeter base level when constructing
Whether you are building wooden or brick perimeter base, it is crucial to get right measurements. You simply don’t have room for error. So, one of the main cons of perimeter base greenhouse foundation is that it is quite hard to keep level when assembling the base.
Also, perimeter base is normally larger that the greenhouse. For example, a perimeter base should be 10′ x 12′ to support a 8′ x 10′ greenhouse. There are some debates around using pressure treated lumber for greenhouse base as chemicals can leach into the soil.
Although you can go for a naturally rot resistant wood like cedar, it can be quite pricey. Nevertheless, you will still need to look after the wood and it is not as durable as other options. It is more prone to be affected with fungus, so you need to think about getting rid of mold in a greenhouse.
3. Paving slabs base is only suitable for growing in pots
It is a permanent type of foundation, so it is not suitable for temporary structure or if you are looking to site a greenhouse somewhere else later on. Also, you will only be restricted to growing in pots or grow bags which might not be suitable for some plants.
Moreover, I know many gardeners who start off with a small greenhouse structure and then say that with time it is not enough for a big collection of plants. Finally, the costs of laying paving slabs are higher in comparison to building brick or wooden perimeter base.
4. Standing water can be a big problem with concrete foundation
Concrete foundation is uniform, so during watering moisture will collect on the surface. Standing water can increase humidity and provoke mold development. In the greenhouse with concrete base water can only drain away around the edges of the greenhouse base.
To avoid this, you need to drill the drainage holes in the base. It can work for some time but the best option would be installing greenhouse drainage like a French drain. Similarly to paving slabs base, you can only grow in pots with concrete foundation.
Finally, concrete base is the most expensive option especially if you hire a contractor. Laying concrete foundation on your own can be tricky and time consuming. It can be quite hard to lay a slab of concrete large and deep enough to support a heavy greenhouse structure.
If you have a medium sized greenhouse and are planning to use it mainly for propagation and keeping potted plants, then concrete foundation is the best option. However, if you are going to use a hobby greenhouse on a daily basis, laying paving slabs base is a perfect solution as it drains well and is easy to maintain.
For small greenhouse owners with a limited budget it makes sense to build brick or perimeter base and fill it with gravel for flooring. It will provide the necessary support for the structure and gravel floor will ensure good drainage.
Also, take a look at The Greenhouse Catalog, they offer durable and weed blocking flooring solutions. You can find more information on the best greenhouse flooring option here.
Did you build a foundation for your greenhouse? Let me know in the comments section below!