Even though your area might not be affected by flooding, the greenhouse can be in a danger of mini indoor floods.
The water which is used to irrigate the plants inside the greenhouse can accumulate and cause damage to the floor.
If you have plants in the pots, the water can still percolate through them onto the basement whilst making it really muddy and slippery.
What do I need to do to avoid that? Well, a good option is to have some sort of the greenhouse drainage system.
What is a greenhouse drainage system?
A drainage system is a process of carrying off the excess of water through an arrangement of pipes. The rain water naturally seeps into the soil.
A drainage system prevents the rest of the rain water from running towards low-lying ground by directing it into the rivers and creeks and ending up in the bay.
Do I need a greenhouse drainage system?
A drainage system below the basement of the greenhouse will collect the water falling to the floor and will direct it to a specific location out of the greenhouse where it can be safely dispensed.
If you have a garden I strongly recommend having at least the simplest drainage. The excess water not only inside the greenhouse but outside it is a massive problem.
As I have already mentioned, the water from the plants makes the floor very muddy so it is easy to slip.
Also, water quickly becomes stagnant which puts your plants in danger by providing the favorable conditions for pathogens growth.
If you don’t have a drainage system in your backyard the rain water is not going to the designated area, therefore it can damage the foundation of your house or flood a basement and so on.
What is the best foundation for greenhouse drainage?
I recommend considering whether you want to plant your plants directly in the soil or have some sort of the foundation.
I would stay away from planting directly into the soil because you will have to change the soil quite frequently to avoid the diseases.
However, my parents have a greenhouse which is set up directly on the ground. In terms of drainage you have to assess the soil in your garden.
If the soil is permeable, the drainage is going to be sufficient. You might want to leave a half of the ground to plant the plants directly.
It is a good idea to cover another half with gravel to have a clean space where you can put a working bench.
So, what are the most common foundation options? There are two types of foundations for the greenhouse: concrete and paving slabs. How does the foundation affect drainage?
Well, if you go for the paving slabs these will provide the natural drainage to your greenhouse. The gaps between the slabs allow the water to escape through them into the ground.
Greenhouse Concrete Base Drainage
If you just lay the concrete foundation the water won’t have any natural escape and will accumulate on the floor forming paddles.
To avoid that you need to make sure that the surface is sloped away when pouring a concrete. An approximate drop of 1/8 to 1/4 per linear should do.
Greenhouse Guttering Systems
It is very important to plan the outside drainage as well as the inside one. Without any guttering system the rain water running from the roof of the greenhouse structure will drip off the ends onto the soil.
This will affect the soil, for example, by forming holes in the ground. Also, guttering system allows you to collect rainwater which is ideal for some plants.
So, you can either collect the rainwater by using a guttering system or a swale. I would consider having a swale if I had a freestanding greenhouse.
Alternatively, I would set up a system of gutters if my greenhouse was attached to my home. Some of you might ask what is a swale and why do you need one.
OK, let’s answer these questions!
A swale is a trench in a tract of land which increases rainwater infiltration, filters pollutants and manages water runoff. If you have a swale near your greenhouse the rainwater dripping from the ends will slowly penetrate the soil.
On the other hand, you can use a system of gutters, downspouts and drain pipes to collect the rainwater into the rain barrels. It is quite easy to set up and the elements are extremely affordable.
Of course, there are pros and cons of a swale and guttering system but you should have at least one of them.
What is the best drainage for greenhouse?
A French drain system is the best drainage for greenhouse if you noticed that the water logging drainage problem became very serious.
So, what is a French drain (also known as a trench drain)? Essentially, it is an underground drain pipe.
You need to dig a pipe a gradient and then fill it with aggregate. This allows the surface water to drain away from the area which is prone to flooding.
Overall, a French drain is a good option to carry away the surface water building up in waterlogged areas around the greenhouse.
The advantage of having a French drain as a drainage system is in its simple and cost effective construction. Also, the project can be easily done without any special tools and complicated equipment.
All you have to think about is where to dig the trench and where to direct the excess water to.
It is very important to make sure that rainwater and runoff are not drained into foul water drainage.
Foul drainage carries used water from the property (from toilets, sinks, showers, washing machines and etc.). Mixing this two up can lead to the risk of pollution with harmful chemicals.
Remember to check the building regulations of your area for the planned drainage system!
How to install a French drain for a greenhouse?
I am going to share with you an easy and quick step-by-step guide on how to install a French drain in your garden to drain the excess water from your greenhouse.
Step 1 – Dig two trenches 12″ deep and 6″ wide.
One under the middle of the walking path inside the greenhouse and another one down the end wall outside the greenhouse.
Keep the trench at least 1 meter away from your structure. When diffing your trenches make sure that the bottoms are sloping gradually downhill approximately at a rate of 0.25″/foot.
Use a level to check the slope to check that the slope drops 1″ over the length of the level.
The sides of the ditch should slope away from the greenhouse at minimum 45 degrees angle to make sure that the surrounding soil remains stable.
Step 2 – Carry on digging the ditches under the end wall of the greenhouse and outside.
You should reach a point where the slope drops off. Now you can terminate the trenches without loosing a slope at a ratio of 1:50.
Step 3 – Line the trenches with a stripe of drainage cloth.
Make sure to cover the bottom and both side of the trench completely.
Step 4 – Put inside the trench a perforated drain pipe.
Also, use couplings to connect the multiple pieces.
Step 5 – Cover the pipe with coarse gravel.
The pipe should be covered completely. Moreover, fill the inside of the drainage cloth up to 3″ of the top of the trench.
Fold the drainage cloth over the covered with gravel pipe and fill the rest of the space with with more gravel. You should get something similar to this picture.
I hope you find this information useful and can use the following options for your greenhouse. Please let me know what you think and I would like to hear your opinions on this topic.
Happy greenhousing everyone 🙂
