Soil has several functions with respect to plants: it anchors and protects the roots; it provides water and nutrition; and it establishes links with other organisms (parasites, other vegetation, etc.). However, soil itself is not essential, as these functions can be performed by other substrates: this is the case with so-called "soilless" or "out-of-soil" crops.
Hydroponic cultivation (or hydroculture) is a soilless cultivation system in which plants are fed a nutrient solution composed of water and essential elements. The roots can be immersed directly in the solution or placed in an inert and aseptic substrate, which is chemically and biologically inactive and therefore also devoid of nutrients. In the latter case, the nutrient solution reaches the plants through irrigation of the substrate, which can be expanded clay or coconut fibre, for example.
With a hydroponic system and due care and attention, you can potentially grow all types of plants (vegetables, aromatic, medicinal or ornamental). In this article we will find out how to build a hydroponic system for installation in a DIY hydroponic greenhouse.
Why build a hydroponic greenhouse
There are various systems for hydroponic cultivation, which differ depending on the presence or absence of substrate, the nutrient solution administered to the plants, the space needed, running costs, etc. Examples of hydroponic systems are NFT (nutrient film technique), drip system, DWC (deep water culture), and ebb and flow (also called "flood and drain").
In any case, in a hydroponic system the plants receive everything they need to develop (water, nutrients and oxygen); they grow in a controlled environment (in terms of the type and quantity of nutrients, pH and concentration of the nutrient solution, temperature, light etc.), protected from parasites and pathogens normally present in the soil.
Compared with soil cultivation, hydroponic cultivation can be done anywhere, even in unfavourable environments with adverse conditions in terms of climate and soil. With this technique you can grow plants in a hydroponic greenhouse (i.e. one that you build yourself in the garden), or even in the home (there are even stylish mini hydroponic kits that double as designer furnishing items).
A hydroponic system needs less water to grow plants and does not require herbicides. Fertilisers are supplied in precise doses through the nutrient solution, according to the crop’s needs at each stage of its life cycle (growth, flowering, production). Similarly, pesticides are applied in small amounts (as humidity can promote fungal diseases). Therefore, since there is no wastage of water or dispersion of fertilisers and pesticides, the environmental impact of hydroponics is more limited compared with cultivation using soil.
DIY hydroponic system: how to build one
Let's now see what you need to build your own simple and inexpensive hydroponic drip system for a DIY hydroponic greenhouse, which we will describe in the next section:
Plastic tank with capacity for around 50 l of nutrient solution: choose the most suitable size based on the space available in your hydroponic greenhouse (we are basing our example on a "cultivation module" for four seedlings).
Plastic pot for holding the substrate and the plant: must have the same dimensions as the solution tank, except for a lower height.
Air pump with oxygenator to mix and oxygenate the nutrient solution.
Immersion pump to operate the drip irrigation system, by drawing solution from the tank so that it can be conveyed to the plant pot.
For the irrigation system you need: 1 m length of Ø 16 mm watering tube, 1 T-piece and two 16 mm end plugs; 1 m length of 5 mm micro-irrigation capillary hose, four 5 mm plugs, four drippers.
Other: for example tools to monitor the parameters of the nutrient solution (pH, electroconductivity, temperature).
A hydroponic drip system is a closed cycle system, which means that excess nutrient solution that isn't absorbed by the plants is recovered and recirculated into the irrigation system. Here are the steps for making one:
Drill a hole in the centre of the plant pot base: this is where the watering tube of the hydroponic system will be routed.
Make several smaller holes at the bottom of the same pot so that excess water can drain into the nutrient solution tank (a 3 mm drill bit should do). One of these holes, positioned in a corner, will be used to route the air pump tube.
Cut a length of watering tube and insert it into the central hole; insert the air pump tube into its corresponding hole.
At the bottom of the nutrient solution tank, place the submersible pump and the air pump oxygenator.
Attach the watering tube to the submersible pump and route its power cable over the top edge of the tank; connect the air pump tube to the oxygenator.
Insert the plant pot into the nutrient solution tank.
Shorten the watering tube (the supply tubes, which will water the plants, should reach the edge of the plant pot) and connect it to the central connector on the T-fitting, tightening it securely to avoid water and pressure leaks.
Cut another two lengths of 16 mm pipe, join them to the T-fitting and plug them with the end plugs: they will be the tubes supplying the drip solution of your hydroponic irrigation system.
Make two holes in each of the supply tubes using an awl, then insert the 5 mm couplings for the capillary tubes into the holes (carefully, to avoid leaks as before).
Cut 4 lengths of capillary tube, then connect them to the couplings and, at the other end, to the drippers.
Your DIY hydroponic system is almost ready. Once everything is cleaned, fill the nutrient solution tank with water and nutrients in the recommended ratio; spread expanded clay (or other substrate) in the perforated pot; and finally plant the plants and orient the drippers close to them.
To fill the tank of your DIY hydroponics system you can use tap water (let it rest for about 48 hours in order to evaporate chlorine). Rain is also an excellent water source: you can fill the nutrient tank using a water pump to draw rainwater collected in a water butt. Using rainwater will make your hydroponic system cheaper and even more eco-friendly.
How to build a DIY hydroponic greenhouse
Once completed, the hydroponic system should be placed in a DIY hydroponic greenhouse. How to build one? You can buy an off-the-shelf greenhouse formed by a metal structure and protected with sturdy plastic sheeting, the kind used to shelter the tenderest plants in winter.
Alternatively, you can build a cabinet-type hydroponic greenhouse made of wood or metal, using wooden strips or U-shaped sheet metal profiles for the uprights and crosspieces, assembling them with screws and (for the doors) hinges. To close the greenhouse on all sides, simply use strong plastic sheeting (fixed with drawing pins to the wood of the load-bearing structure) or honeycomb polycarbonate panels (screwed to the wooden or metal structure).
Install shelves in your DIY hydroponic greenhouse to place your hydroponic tanks onto. You can make the shelves from recycled materials, such as pallets cut to size using a handy battery-powered chainsaw. Even for simple craft projects like this, remember to wear the right protective clothing and follow the guidelines for using a chainsaw safely.
Whether you use polycarbonate sheeting or plastic sheeting, the greenhouse covering must be transparent. This is because it is essential that the hydroponic greenhouse lets in plenty of sunlight, otherwise the photosynthetic efficiency of your plants will be compromised.