A Gravity-Fed Home Hydroponic Garden System
Seeking simplicity and efficiency of operation in growing food hydroponically, I designed and built the Gravity-Fed Hydroponic Garden (GFHG). The garden uses no electrical input (e.g., pump; timer; air bubbler; lighting) typically found in highly automated hydroponic systems. Instead, the GFHG eliminates these inputs by means of a small, low-cost float valve. What follows is a description of the system components, its construction and operation, results from an initial trial of the system’s performance, management of the system, and a brief discussion of its pros and cons.
Components of the GFHG
Figure 1. The Gravity Feed Hydroponic Garden System The GFHG has three main components: (1) a series of 16 opaque, five-gallon inter-connected Grow Buckets (GBs) filled with a mixture of perlite and peat moss; (2) two five-gallon Control Buckets (CBs) each containing a float valve for regulating the level of nutrient solution in the GBs; and (3) a 27-gallon reservoir of nutrient solution connected to each of the CBs. The garden is divided into two separate but equal parts. Figure 1 shows the initial setup of one side of the system with cabbage, tomato, eggplant, pepper, and squash plants.
Construction of the GFHG
The first step in building the GFHG is to prepare the GBs. This involves: (1) Drilling holes at the base of the GBs to insert half inch poly tube for connecting the buckets with PVC fittings; (2) putting a five-gallon cloth paint strainer inside each GB to hold the substrate in place; (3) filling the GBs with about 9 liters of nutrient solution; and (4) filling the GBs with a mixture of perlite/peat (or any other suitable grow media) to about three-to-four inches from the top. The nutrient solution slowly percolates upward to moisten the substrate and may cause it to compact and sink a little more. The GB is ready for planting when the substrate feels slightly moist on or just below the surface.
Left – Figure 2a. Float Valve Assembly | Right – Figure 2b. Reservoir Connection Preparation of the CBs is shown in Figure 2a, the float valve assembly and its placement inside the CB about 4-5 inches from the bottom, and Figure 2b, its connection to the nutrient reservoir. The final step is to connect all the buckets with poly tube and ball valves.
The layout of the system in a square configuration minimizes the space between the GBs and distance that the flow of nutrient has to travel from the reservoir. Seeds can be sowed directly into the substrate with light watering to facilitate germination. A second option is to grow seedlings in net pots and/or seed starters (e.g., rockwool cubes; clay pellets; etc.) and then transplant them into the GB.
System Operation
As plants grow and take up nutrient in the GBs, the level of the nutrient solution in the two CBs begins to drop. This causes the float valve to open, releasing nutrient from the reservoir into the CB by the force of gravity and distributing it to the GBs as needed. When the CBs reach the point where the plants no longer need to draw more nutrient, the float valve closes. The action of the float valve maintains a roughly constant and equal amount of nutrient solution in the GBs. The system continues to self-water until the nutrient solution in the reservoir is depleted and needs to be refilled.
System Performance
Left – Figure 3a. Tomatoes | Middle – Figure 3b. Cabbage | Right – Figure 3c. Squash The first set of crops that were planted and harvested in the system included tomatoes, cabbage, and squash grown under typical climate conditions during the spring and early summer in southern California as shown in Figures 3a, 3b, and 3c. The system worked nearly flawlessly. One of the two float valves became clogged by algae that accumulated in the reservoir. The yellow top of the reservoir allowed sun light to penetrate the nutrient solution and create a thin layer of algae growth on the surface.
This problem was remedied by placing a black piece of plastic under the yellow top. Otherwise, there were no mechanical malfunctions.
Management and Maintenance
GFHG operated autonomously until it was time to harvest and prepare the GBs for re-planting. This was done by (1) closing the ball valves on both sides of a GB, (2) disconnecting the poly tube to allow the spent nutrient to drain out, (3) extracting the plant from the substrate, and (4) emptying the remaining substrate from inside the strainer net into a container. Then allow the strainer to dry, pick out the root mass, and reuse it as well as the substrate. After preparing a new GB, reconnect it to the rest of the system.
Pros and Cons
In terms of quantity and quality of yield, the GFHG exceeded expectations on the initial trial. The GFHG is best suited for “heavy feeder” plants (e.g., tomatoes, cabbage, broccoli, brussels sprouts, etc.). It can utilize different substrates such as a perlite, peat, clay pebbles, pumice, coco coir, or various mixtures of these elements in order to customize and create the optimal growing environment for your crops. A self-watering system that does not depend on electrical input devices is cost-saving, reliable, and durable as long as the size of the nutrient reservoir is large enough to accommodate the number and types of crops throughout their growth cycle. On this latter point it became clear as more plants advanced to later stages of their growth that the nutrient in the 27-gallon reservoir depleted quite rapidly and required replenishment almost on a weekly basis. A larger nutrient tank was clearly needed (i.e., 42-gallon barrel) in order to extend the operation of the system without intervention.
There are two additional issues with the GFHG that are worth mentioning: (1) pH control; and (2) nutrient management. Measuring and adjusting the pH level of the nutrient solution on a regular basis are basic tasks for successful hydroponics gardening. pH corrections done in recycling systems are very efficient and produce immediate results. Nutrient balancing in the GFHG is very slow to take effect because only small amounts of nutrient are replaced in each of the GBs at any given time.
Some nutrient formulations are designed to promote optimal plant growth at different stages of a plant’s growth cycle: healthy roots (Stage 1); leaf mass (Stage 2), and fruit production (Stage 3). Different plants grow at different rates and mature at different times.
The GFHG described here grew nine different varieties of crops all with varying planting and harvest times. In this setup, using a multi-part nutrient would be unworkable and ineffective.
Conclusion
A GFHG runs counter to the growing market for high cost home hydroponic units with automated lighting, aeration, irrigation, and water monitoring functions designed to improve efficiency and simplicity of operation for growing small crops. There is a big difference between the two types of systems. Manufactured systems gain their efficiency and simplicity through automation whereas a GFHG achieves its efficiency and simplicity through the elimination of automation. A gravity-feed, self-watering hydroponic garden may an attractive option for outdoor home hydroponics by reducing operational costs, expanding crop diversity, and eliminating potential mechanical and/or electrical issues associated with highly automated gardens.
