Hydroponic Cultivation System Options
Hydroponic cultivation has many advantages. It reduces the high variability in quality and potency that can be found in outdoor-grown plants by providing a stable environment and abundant nutrients. Indoor hydroponic growing also reduced the potential for cross-fertilization and is discrete. There are several hydroponic methods that can be used for cultivation. For any system to support plant growth it needs to efficiently provide plants with nutrients and oxygen.
Hydroponic Cultivation Techniques
- Standing Arated Technique (SAT)
- Deep Water Culture
- Nutrient Film Technique (NFT)
- Drip and Pass-Through Systems
- Ebb and Flow
- Wicking Systems
The main elements of a hydroponic system are the nutrient solution, the oxygen source, the containment system, and the optional use of a soilless growth medium. Systems may be open, meaning the nutrient solution is used once then drained and discarded, or closed systems where nutrient solution is filtered and reused. The other main variable of hydroponic systems is whether oxygen is supplied by a pump or whether it is supplied from the air. Most systems can be operated both ways.
A true hydroponic system supports plant life with the roots suspended in an aerated nutrient solution or in a nutrient solution that flows through a root channel and does not utilize any rooting medium. Some soilless growing systems have come to be called hydroponics in a broader sense of the word.
Aerated Water Culture Systems
Standing Arated Technique
The standing aerated technique (SAT) is a true hydroponic system consists of a rooting vessel, usually a bucket, filled with nutrient solution, and an air tube connected to a pump that continuously bubbles oxygen into the solution. The bubbling oxygen from the pump provides oxygen to the roots and also stirs the nutrient solution. The plant is suspended over the solution using a soilless medium filled basket that hangs through the lid of the bucket or using a floating foam platform with a hole for the roots to dangle through.
Nutrient solution needs to be fully changed according to the type of solution used. Most nutrient solutions need to be changed weekly. Generally, 2-4 gallons of solution is needed for each plant in an SAT system. Water lost to the plant needs to be replaced daily, either with plain water or with water containing nutrient solution at ~10% of its normal concentration. Since the solution needs to be adjusted and water added frequently, the standard aerated technique is not the best suited for commercial growing.
Deep Water Culture
Deep water culture is a more specific version of this basic hydroponic system. Specifically, deep water culture systems use 8-10 inch deep nutrient solution. It is generally best when the water level does not contact the basket that holds the plant, but some contact may be desired if roots have not grown through the basket yet. Bubbles from the air pump should splash the bottom of the basket as they float to the surface of the solution and burst. When the basket makes full contact with the solution, waterlogging can easily occur.
Bucket systems can be easily modified to connect several buckets to a control bucket of solution that recirculates. In recirculating systems, the air pump is only needed in the control bucket where adjustments and monitoring of pH and electrical conductivity (EC) are made.
Flowing Water Culture Systems
Nutrient Film Technique
The nutrient film technique (NFT) grows plants in a stream of nutrient solution that flows through the roots. Nutrient film troughs slope slightly to keep water flowing down, and recirculate solution through a filter, then back to the top of the trough using a pump. A diluted nutrient solution can be used to add back water and nutrients consumed by the plants. Like with SAT systems, pH and EC need to be monitored and adjusted periodically.
Solution flow can be placed on a timer that alternates on and off or can be circulated in a half on/half off cycle. The recommended nutrient solution flow rate for an NFT system is 1 liter of solution per minute. The flow rate of the pump will have to be adjusted as root mass increases and slows the flow of solution. NFT systems face some additional challenges because oxygen and nutrient concentration can be depleted by plants at the top of the trough that make the first contact and deprive plants towards the bottom of the channel.
Drip systems are similar to NFT systems in that they provide a stream of nutrient solution that is pumped up from a reservoir and applied to the soilless medium around the plant using drip irrigation piping. The plant container filled with a soilless medium can be set on top of the reservoir so excess water drains back into the system, or the drained solution may be discarded and the used volume can be replaced with a fresh solution.
Another version of the drip system is a pot or bucket (such as BATO bucket) which is filled with a soilless growth medium. Holes in the bottom of the bucket allow for drainage, and drip tubing is likewise placed at the base of the plant. Plants can be directly planted in these systems using the rockwool or coir block they were germinated in.
Ebb and Flow Trays
Ebb and flow (flood trays) are a third hydroponic technique that does not utilize an aerator. Plastic or waterproof plywood trays can be flooded with nutrient solution to cultivate plants that are sown in 1-2 inch growth blocks or another soilless medium. Flood trays are usually closed systems that recirculate the nutrient solution until it is spent. A reservoir collects solution as it drains from flooding the tray and a pump recirculates it to a tank to be reused. The roots receive oxygen as the solution drains out of the tray.
Timing for flooding can be adjusted based on plant needs and water holding capacity of the rooting medium. Before the solution is reused, water is added to make up the volume absorbed by the roots of the plants. At this time pH and EC can be tested and adjusted as needed. The solution should be filtered before the next flooding.
Passive Aeration Systems
Wick systems are very simple systems where a bucket containing nutrient solution is placed under a bucket containing soilless growth medium. Holes in the center of the bottom of the planting bucket and in the lid of the nutrient solution bucket allow a felt or rope wick to pass through. The nutrient solution travels up the wick to supply the plant with moisture. Several wicks may be needed to supply large plants with enough moisture and nutrients. Air pockets in the growth medium supply the roots of the plant with oxygen so aeration is not needed but may be used to keep the solution from settling.
In aeroponics, plant roots are continuously misted with nutrient solution. The plant is supported on a tray which allows roots to dangle into the tank below. Some nutrient solution accumulates in the bottom of the tank and is recirculated through the misters which spray the dangling plant roots. The roots of the plant grow in the air and receive ample oxygen. Droplet size and misting frequency are variable. Generally, better results are achieved when roots are exposed to a continuous fine mist which leaves a small accumulation of solution in the bottom of the misting tank. Nutrient solution concentration has to be adjusted for frequency and exposure time of solution to the roots.
Selecting a System
There is a large variety of hydroponic systems available, and many systems can be built quite simply. Aerated bucket systems, drip systems, and wicking bucket systems are both very simple systems to start with. Systems like the GH Water Farm or Flo-n-Gro Bubbler Bucket are inexpensive and ready to use. More advanced recirculating deep water systems like the Current Culture Under Current are more expensive and require more upkeep than a new grower may be ready for. Most systems can be easily modulated to scale up, but new growers will likely want to start small since it will take time to learn to use the systems to their full potential.
Is hydroponic cultivation better than soil?
There is little evidence that growing plants hydroponically increases overall yields or potency. High-quality plants can be attained in systems with or without a soil-based growth medium. With the large variety of hydroponic systems available, it is difficult to make broad claims. Some systems can be highly efficient in conserving water use, while others may consume more water than would be used for irrigating plants in soil. Hydroponic systems do have the advantage of having generally lower pest and pathogen exposure. Systems are most commonly used indoors or in greenhouses but can be used outdoors as well. In areas where soil quality is low, it can be less labor-intensive to use the space for hydroponic cultivation instead of trying to improve soil quality. Hydroponic systems do require technical knowledge, daily upkeep, and monitoring, but involve less manual labor, especially compared to outdoor cultivation.