Hydroponic gardening has been growing in popularity among home gardeners and small-scale farmers due to several key benefits. By delivering nutrient-rich solution directly to plant roots rather than soil, hydroponics allows for faster growth times, higher yields in smaller spaces, and easier control of nutrients compared to traditional in-ground cultivation.
One increasingly utilized hydro technique is the recirculating deep water culture system (RDWC). This method involves suspending plants in net pots over channels of aerated, nutrient-rich water that continuously recirculates via electric water pump from a reservoir.
Constructing even a modest RDWC setup can sustainably grow various vegetables and herbs with much higher yields per square foot compared to soil, benefitting the self-sufficient gardener. This article provides detailed guidance on designing and installing a fully-functioning recirculating deep water culture hydroponic system at home for optimal plant growth and health.
What is an RDWC System?
A recirculating deep water culture (RDWC) system is a subtype of the broader hydroponic gardening methodology, which involves growing plants in nutrient-rich water rather than soil. RDWC uses a flooded, oxygenated reservoir that continuously circulates solution to multiple planting beds or tubes via electric water pump. It’s considered a “constant flow” technique.
The oxygenation provided by air stones combined with the recurring flow of aerated water enables rapid growth rates and higher yields compared to other hydro methods. The continual circulation safeguards against problems like stagnation and lack of oxygen. It also allows for easy application of nutrients across all plant sites.
Img: Recirculating Deep Water Culture System Schema
In RDWC, net pots containing seedlings sit suspended above channels of recirculating water, generally about 3–8 inches deep. An inert medium like expanded clay pellets surrounds roots emerging through pots, while the remainder stays submerged. Plants in this system get 100% of nutrients and moisture requirements directly from the perpetually circulating, aerated solution.
Home RDWC systems allow indoor gardening in limited spaces year-round. They commonly utilize materials like plastic containers, PVC piping, water pumps and air stones that are affordable and easy to configure into a productive system. Once running, RDWC requires monitoring and replenishing of the central nutrient reservoir about once a week on average. This recurring deep water culture technique is emerging as a preferred hydroponic approach for home use.
How Does Recirculating DWC Systems Work?
A recirculating deep water culture system relies on the interaction between several components to function successfully. It begins with an electric water pump submerged in a central reservoir filled with nutrient solution. Tubing connects the pump outlet to raised grow channels that house the plant roots suspended in net pots. Additional tubing then returns solution from the channels back down to the reservoir in a closed loop flow.
Air stones connected to an air pump are placed in both the central reservoir and grow channels to infuse dissolved oxygen throughout the system. This oxygenation energizes root development and plant growth. The recurring circulation of aerated water also prevents stagnation, which reduces risks of root rot.
Img: Deep Water Culture System Schema
The pump circulates solution from the reservoir up to the raised grow channels in a timed flood and drain sequence, generally 15 minutes on and 45 minutes off. So plant roots get bathing in nutrient solution then time to breathe air before the next flood cycle.
This continual recirculation equalizes pH, nutrients, and temperature for all plants regardless of location. The system maintains optimal growing conditions with little effort once dialed in and running smoothly. Monitoring nutrient levels, pH, electrical equipment, and refilling the reservoir is essentially the only routine maintenance required in a home RDWC system between harvests.
Recirculating Deep Water Culture (RDWC) Hydroponic Grow Kit System
- Reservoir Bucket Connected to 4 Grow Buckets
- 400 Gallon/hour Circulating Pump
- Large 5 gallon square buckets, pre-drilled
Comparing RDWC and DWC Hydroponic Systems
Recirculating deep water culture (RDWC) and standard deep water culture (DWC) systems share some fundamental similarities in their approach to hydroponic gardening, but also have distinct differences.
Both utilize air stones connected to growing containers in order to oxygenate the nutrient solution. They both also position plants in inert grow media above reservoirs that submerge part of the roots while allowing upper parts to emerge. This oxygen to root zones while providing full nutrition and moisture requirements for vigorous growth.
The key difference lies in the continuous flow and return of nutrient solution from a central reservoir in RDWC systems, compared to the generally static nature of individual DWC containers.
In RDWC, an electric pump perpetually circulates the central, aerated reservoir solution throughout all growing tubes in a closed loop. This recurring flow equalizes conditions, prevents stagnation issues, and enables larger scale systems. The stationary solution in basic DWC requires more overall monitoring and individual attention per site.
| Component | RDWC | DWC |
| Water Flow | Continuous closed-loop recirculation via electric pump | Static individual containers |
| Scale Potential | Expandable, supports numerous grow sites | Limited number of individual sites |
| Central Reservoir | Maintains centralized solution | No common reservoir |
| Maintenance Needs | Less overall effort once running | Greater individual container oversight |
| Stagnation Risk | Lower from perpetual flow | Higher in static solution |
RDWC provides excellent aeration, reduced stagnation tendencies, and scalability compared to standard deep water culture systems. Both can produce robust hydroponic plants, but RDWC is emerging as the preferred technique.
Advantages Of A Recirculating Deep Water Culture System
Utilizing a continuously circulating nutrient reservoir provides RDWC systems with distinct benefits over other forms of hydroponic cultivation. The major advantages of operating a recirculating deep water culture system include:
- Increased Oxygenation and Healthier Roots. The perpetual motion of water over air stones dissolves and distributes more oxygen throughout the system, stimulating stronger, healthier root zone development. Roots thrive submerged in the highly oxygenated solution.
- Reduced Risk of Root Disease. The recurring circulation from a common, aerated reservoir flows fresh nutrient solution to all plant sites while diluting any potential localized issues. This continual motion and oxygenation significantly lowers the chances of root zone problems taking hold compared to stagnant hydro systems or individual containers where water and/or oxygen can be cut off, enabling pathogenic bacteria or fungi to rapidly infect entire root structures. RDWC’s perpetual flow and air infusion keeps roots vigorous.
- Uniform Growing Conditions and Growth. Drawing complete nutrient and water requirements from one shared central reservoir maintains consistent parameters like nutrient concentrations, pH levels, water temperature and dissolved oxygen throughout the entire system. As such, plants generally grow at a uniform, even pace across the RDWC garden with more limited issues of lagging or struggling vegetation since the perpetual solution equilibrates everything automatically.
- Greater Efficiency and Density in Limited Spaces. The optimized oxygenation and disease resistance allows RDWC systems to support a higher overall plant density compared to soil plots and many other hydro techniques. By maximizing yield-per-square-foot, home gardeners can sustainably grow more vegetables and herbs even in indoor spaces with lighting systems.
- Ability to Operate Effectively with Minimal Oversight. The closed-loop flow and centralized reservoir of RDWC allows for automated circulation and periodic nutrient dosing adjustments to the singular holding tank. This means that once all equipment is confirmed functional with safety checks in place, the system can essentially run itself for days if not weeks before needing monitor checks. Grow lights and air flow would still require periodic inspection, as with any indoor garden.
Leveraging a perpetually recirculating central nutrient solution to bathe roots enables improved plant health, standardization, scalability and efficiency in home hydroponic cultivation.
Drawbacks of a Recirculating Deep Water Culture System
While having considerable advantages, utilizing a recirculating hydroponic system also comes with some potential downsides to consider:
- Higher Initial Equipment and Setup Costs. Constructing an RDWC system with all required components like tubing, water pump, timers, reservoir containers, and other accessories can run anywhere from $300 up to even $2,000+ for more extensive builds. This represents a notable upfront investment compared to basic hydroponic methods that utilize more affordable individual containers and minimal specialized equipment.
- More Intensive Maintenance When Issues Arise. Due to the interconnected nature of RDWC systems, problems like pump failures, timer malfunctions or leaks can impact other components and require more complex troubleshooting and replacement procedures compared to diagnosing a standalone DWC container system. Resolving breakdowns often necessitates at least some disassembly to access equipment.
- Increased Risk from Centralized Failures. With full dependence on a single central reservoir, issues like water pump defects, power outages affecting the pump or timers, rapid pH fluctuations, or accidental contamination of reservoir solution poses larger scale risks in RDWC systems since the deficiency or damage impacts all connected grow sites simultaneously. Other hydro techniques based around individual containers have less expansive correlations.
- Limitations for Expanding Scale. While RDWC systems provide excellent efficiency for larger home installations, they can reach limitations if trying to perpetually expand the number of grow sites supported off a given reservoir volume and fixed pump circulation capacity. Either necessitates adding a second standalone system or upgrading pump strength and reservoir scale.
- Need for Diligent Safety Practices. When handling water, electricity, and drainage aspects, RDWC builders must exercise diligence around leak points, avoiding pump/element contact with solution, positioning electrical hardware properly to avoid sparks or exposure, and routing excess drainage from potential early leaks safely. Failure to separate high voltage aspects from water circulation risks electrocution hazards. Proactive safety is essential.
How To Set Up a Recirculating DWC System?
Constructing a properly functioning recirculating deep water culture hydroponic system involves integrating various components into a closed-loop flow system. The main pieces of equipment needed to include pump(s), tubing, timers, growing containers, a reservoir, air stones, waterproof lighting (for indoor systems) and other accessories fitting for the desired scale. Configuring the layout and equipment for smooth recirculation while optimizing plant spacing takes some planning and handy skills.
Assemble The Reservoir
Obtain a plastic container or bucket large enough to hold the full volume of nutrient solution needed for your system. The reservoir should be opaque or painted black to prevent light getting in and promoting algae growth.
Set up the water pump inside the reservoir. Use tubing to run from the pump outlet up to the grow site and back into the reservoir in a closed loop. Install an air stone connected to an air pump in the reservoir to oxygenate the nutrients. Oxygen is critical for healthy roots.
Prepare Containers
Acquire polystyrene or plastic grow buckets, pots, or tubs with drainage holes for each plant. Cut small slits near the top to hold plants in place. Fill the containers with a medium like perlite, vermiculite or clay pebbles to support the plant roots.
Alternatively, get a ready-made raft system with slots for plants built into foam boards that float on the nutrient solution. Position larger plants towards one end to prevent overshadowing.
Put Plants Into System
Gently place pre-grown seedlings or stem cuttings with established roots through the openings, so the root mass hangs beneath the container into the empty space where water will flow. The roots immediately get constant moisture but also lots of oxygen.
Turn on pumps once plants are anchored in place to start circulating the water and nutrients. Monitor the system closely at first to ensure proper flow rates and fill levels before leaving to run automatically. Maintain consistent conditions and perform weekly maintenance for optimal growth.
Preparing The Nutrient Solution
First, research what nutrients your chosen plants need and find a complete hydroponic nutrient formula suitable for your crop. Many premixed solutions are available to simplify this step. Be sure to get one specifically designed for the vegetative and flowering phases.
Next, you’ll need to mix up batches of nutrient solution to flow into your reservoir according to the directions on the bottle. Carefully measure and add each individual element. It’s crucial to get the strength right, or you risk burning your plants with too much fertilizer. Use pH strips to balance the solution between 5.5 and 6.5.
Optimizing Lighting
Start by determining how much light your plants need. Leafy greens and herbs do well with moderate light, while fruiting plants like tomatoes require very high intensity discharge (HID) grow lights. LED grow lights are energy efficient, long-lasting, and available in full spectrum formulations.
Position the grow lights to maximize coverage over the plant canopy. Raise lights higher to cover more plants, or lower to increase light intensity. Use a light meter to check that plants are receiving adequate intensity at the canopy level without overheating the leaves. Adjust as the plants grow taller.
Maintain Optimal pH Balance
Test and record the pH of the nutrient solution daily using test strips or a digital pH monitor. Recirculating hydro systems tend to drift downwards as plants absorb nutrients. Use pH up solution to bring the reservoir back up to the target range if needed.
Additionally, check EC (electrical conductivity) to monitor overall nutrient levels. As plants uptake fertilizer, EC declines. Top up the reservoir with a new batch of nutrients when depletion gets too low. This will maintain nutrient availability and prevent deficiencies.
Common Issues with A Recirculating DWC
While recirculating deep water culture hydroponics provides ideal moisture and nutrient levels for thriving plants, these systems do come with certain maintenance requirements and potential pitfalls.
Managing factors like water quality, equipment functionality, and pathogen control is key to avoiding preventable issues. The following overview covers areas to monitor and troubleshoot when operating a home recirculating DWC setup for best results:
- Waterborne Illnesses. Hydroponic systems carry a risk of spreading certain waterborne illnesses between plants that share the same nutrient reservoir. Root rot diseases like pythium are common and can quickly kill seedlings. Always thoroughly sterilize equipment between crops and check roots for brown, slimy lesions. Replace reservoirs frequently and use beneficial microbes to outcompete pathogens.
- Limited Plant Selection. While most plants can grow hydroponically, some species are better DWC candidates. Stick with quick maturing greens and vegetables over long season fruiting crops. Focus on leafy lettuces, herbs, spinach, bok choy, peppers, or tomatoes as plants that perform well. Avoid large vines or heavy squash. Start more plants on a staggered schedule for continual harvests.
- Power Outage. A compromised water pump combined with depleted oxygen levels during an electrical outage can rapidly suffocate plant roots and facilitate disease. Get a battery-powered air pump and air stone to sustain oxygenation for at least 12 hours without power. Have a generator or solar panels as backup to restart systems quickly before irreversible damage occurs.
- Water Quality. Tap water containing chlorine or chloramines is toxic to plants. Always start with clean, non-chemically treated water that’s been dechlorinated. Hard water high in minerals causes nutrient lockup issues over time. Either filter water or use distilled. Optimizing water quality prevents many problems in recirculating hydroponics. Test EC and pH routinely.
- Pathogen Growth. Stagnant or unaerated water provides prime conditions for bacterial and fungal pathogen growth. Pseudomonas, pythium, and phytophthora species can rapidly infect vulnerable root systems submerged in contaminated reservoir water, spreading quickly between plants that share recirculating nutrient solution.
- Clogged Pipes. Mineral sediment from hard water or tap water chemicals can accumulate inside pump mechanisms and small irrigation lines. Slow flow or complete line blockages inhibit water circulation. This starves roots of nutrients and oxygen. Routinely flush pipes and replace pump impellers if flow seems restricted.
- Algae Growth. Photosynthetic algae thrive on plant-produced compounds in nutrient rich water. Algae compete with crops for nutrients and block light. Prevent with opaque reservoirs and no light penetration inside pipework. Remove algal growths manually and treat reservoirs with hydrogen peroxide to regenerate clean water.
Keeping DWC systems clean to limit pathogen issues is key, as is proper preventative maintenance on water pumps and lines for uninterrupted circulation. Also be vigilant against green algal growth getting established through good system hygiene and water treatment practices.
Which Plants Can I Grow Using RDWC?
Recirculating deep water culture hydroponic systems provide ideal growing conditions for a wide variety of quick-maturing, high-yield plants. By continually bathing roots in oxygenated nutrient solution, RDWC allows nearly unlimited growth potential not restricted by soil.
The following list covers superb plant candidates that flourish using recirculating hydroponics:
- Leafy Greens. Lettuce, spinach, kale, arugula, and all types of Asian greens thrive under these optimal hydroponic conditions. Their growth rate and yields accelerate greatly compared to soil methods. RDWC leafy greens also maintain tenderness and flavor longer before bolting.
- Basil, mint, oregano, thyme, sage, parsley and cilantro all utilize flowing DWC solution to maximize production of flavorful leaves and cuttings. The extensive root systems stretch freely in protected channels. RDWC herbs yield higher than soil, too.
- Tomatoes, peppers, beans, peas, cucumbers, zucchini and vining crops are highly productive with their roots constantly submerged. Trellising helps stabilize fruiting plants. The clean, protected reservoir prevents soil-borne disease. RDWC is perfect for getting the most from vegetable plants.
- Produce sweet, abundant fruit all season using DWC methods. Column towers with vertical stacking make great use of space. Ever-bearing varieties fruit perpetually with ideal growing parameters. The constantly moist root zone prevents dry periods. RDWC is ideal for getting the highest strawberry yields.
- Microgreens and shoots. Grow rapidly with constant moisture for frequent cut-and-come-again harvesting potential. Shoots and baby seedlings always have optimal hydration and nutrients in RDWC systems. Grow nutrient-dense salad mixes this way.
- Some root crops. Radishes, turnips and watercress actually perform well in DWC instead of aeroponics. Bucket systems allow swelling edible roots to fully submerge while growing suspended hydroponically overall.
FAQ
What temperature should I maintain for nutrient solutions?
Ideal nutrient water temperatures for hydroponic systems range between 68°F - 77°F to balance plant growth rates and disease prevention. Cooler temperatures below 65°F will slow transpiration, nutrition uptake, and overall plant development. However, hot reservoirs over 80°F put root systems at high risk for pathogenic fungal or bacterial illnesses taking hold. Use aquatic heaters and chillers as needed to help maintain consistent temperatures.
What is the recommended frequency for changing nutrient solution?
For a home deep water culture hydroponics system, plan to fully drain, clean and refresh nutrient reservoirs every 2–3 weeks through peak growing seasons, extending to every 4 weeks maximum through winter months. Seedlings, young plants, and times of rapid flowering or fruiting have the highest nutritional demands, so the most frequent solution replacements.
What are the oxygen level requirements for RDWC?
Maintain dissolved oxygen concentrations of at least 6–8 parts per million tested at the root zone level for healthy hydroponic plants. Air pumps connected to water bubbling stones are critical for sufficient oxygenation in standing water systems. Generate the smallest micro bubbles possible to increase surface contact and maximize O2 saturation recirculating around root structures.
How deep should roots extend into the water?
Aim to have individual plant roots suspended 4–8 inches below net pots into free space open to nutrient solution circulation. Too shallow risks drying out thin bottom layers, or density prevents free flow. Overly deep root tendrils increase chances of hypoxia and pathogens taking hold. Find the right balance for each species and system.
Is an air pump necessary for a recirculating deep water culture system?
Yes, an air pump with an air stone is absolutely essential for proper oxygenation of the nutrient reservoir. The bubbles provide oxygen to prevent hypoxia and allow healthy roots to form.
What pump flow rate (gallons per hour) is optimal for RDWC?
Aim for a flow rate of at least 120 gallons per hour (GPH) for a home RDWC system, though commercial systems use up to 300 GPH pumps. Higher flow equals more circulation and oxygen for larger or more plants.
How large should the central reservoir be scaled in a RDWC setup?
Generally, allow at least 5 gallons of reservoir capacity for each mature plant in your system. So, 5 tomato plants would need a minimum 25-gallon reservoir to provide sufficient water volume and nutrients in between solution changes. Scale up accordingly for commercial production.
