Hydroponics, in its purest form, is also referred to as Deep Water Culture or DWC for short. No substrate growing media is required. The plants' roots literally dangle straight into water. Now, for those of you who have been continually warned about over-watering plants, this may seem a little odd. Surely permanently submerging roots in water is a bad thing for all but aquatic plants, right? Well, it turns out that if you bubble enough air into the water and keep it at the right temperature, roots will thrive. Add some mineral-based nutrients and you have a powerhouse hydroponic growing method!
What is DWC / Water Culture?
DWC is the practice of growing plants in aerated water. It's considered by many to be the purest form of hydroponics. DWC systems are very simple. All you need is a container, lid, pump and a net pot. The container holds the nutrient solution (usually around 2.5-4 gallons (10-15 liters)) and the lid supports a single plant growing in a net pot. Roots grow out the net pot and into the nutrient solution held in the container below. In the container, an air stone bubbles away to agitate the solution and keep dissolved oxygen levels high-essential in any DWC system.
Single vs. Modular
Single stand-alone systems are fairly cheap to buy and even more popular for DIY enthusiasts. Modular DWC systems, in which several containers are connected to a central reservoir, create an active system where the nutrient solution is able to cycle from the reservoir around all the pots, arriving back at the reservoir. Both approaches come with their own inherent challenges. Stand-alone systems can be inconvenient to work with, while modular systems can spread problematic root diseases from plant to plant very quickly.
However, get it right and the growth rates and yields possible are astounding.
Q: What types of nutrients and additives work in DWC?
A: Mineral based nutrients. Look for a well-established brand with well-balanced mineral ratios designed for hydroponic applications. Look for a well-buffered nutrient that promotes pH stability in your nutrient solution.
Q: Can I use beneficial biology in DWC systems?
A: This question divides DWC growers. Some growers recommend beneficial biology, some prefer a sterile aqueous root zone. If in doubt, leave them out. If you have propagated your plants in a net pot full of growing medium (such as coco coir chips or something else carbon-based) it is possible that this could provide a habitat for mutualistic organisms at the plant's root crown. But the nutrient solution itself offers little potential for colonization of anything other than bacteria, which while useful, don't offer the benefits of fungi.
Q: Are there any specific pH and EC / TDS requirements for DWC?
A: The usual range (5.5 - 6.5) for pH is fine. 6.0-6.3 is optimal for vegetative growth, and 5.7-5.9 for flowering and fruiting. These specific veg and flower pH ranges will help to ensure that the minerals most needed for each development stage are most available.
Keep EC / TDS on the low side. Try half strength (based on the manufacturer's guidelines) first or even lower when plants are young. Lower EC can result in a higher intake of water into a plant's tissue which, in turn speeds plant metabolism and increases nutrient transport.
Q: How often should the nutrient solution be replaced? How do I know when to replace it?
A: Nutrient solution can typically last 14-21 days but it all depends on the size of your plants and the volume of your nutrient reservoir. You can top off the reservoir with half-strength nutrient solution rather than making up an entire fresh batch. But look out for fluctuations in pH or the nutrient solution becoming murky-if this happens, you might be best to go for a complete change out.
Q: What about nutrient solution temperature?
A: 62-68°F (17-20°C). Above 72°F (21°C) and dissolved oxygen (DO) dips too low. Below 60°F (16°C) and plants tend to slow their metabolism as they "think" the season is changing. Some growers use this to their advantage and reduce nutrient temperature towards the end of the flowering stage to aid in ripening.
Q: How can I monitor dissolved oxygen levels in my hydroponic nutrient solution for DWC systems?
A: You can buy a specialist dissolved oxygen digital meter but they are expensive. Budget meters tend to be unreliable. You will have to spend several hundred dollars at the very least to obtain something fit for purpose. A better bet is to simply ensure that you you're your nutrient solution cool, your nutrient strength modest, and your air pumps running 24/7.
Q: How do I propagate plants for a media-less DWC system?
A: Use an aeroponic cloner to create "bare root" cuttings-perfect for DWC. A major bonus of this method is that we don't want to spend money on bags of growing media after all! Go really easy on the nutrients (1/8 of full strength as per manufacturer's recommendations) and go easy on the lighting - T5 fluorescents (daylight rated lamps). No propagation substrate means no wicking which has a propensity to draw excess moisture around the root crown.
Q: How much of the plant should be submerged in DWC systems?
A: Only bare roots should be submersed, up to the base of the rooted stalk. Do not allow the stem to become submerged. If using a wicking substrate, such as rockwool cubes, ensure the cube is approx. 1" above water line; this may necessitate hand watering for a few days before the roots hit the water.
Q: Are there any other tricks available to the DWC grower?
A: Yes! DWC growers can easily manipulate the amount of moisture in the root zone. This, in turn, can trigger plant responses such as essential oil production, fruiting and flowering. A dryer root zone can increase essential oil production in aromatic crops such as basil and mint. (They do this as a means to conserve water.) A wetter root zone can cause plants to focus on vegetative production, particularly large fan leaves, which in turn speeds transpiration and photosynthetic potential.
Q: Any specific problems or issues that DWC growers should be aware of?
A: Root diseases no doubt, Pythium, Fusarium, etc. Warm water, high nutrient strengths and dirty growing conditions are the culprits.
Q: Do plants in DWC systems grow faster?
A: Yes. A well-hydrated plant typically grows incredibly fast and growers should adapt by shortening vegetative times by around 15-25%.
Q: Are there any specific plants that DWC suits best?
A: Lettuce is what everybody thinks of first-but we are seeing a trend towards using water culture for annual vegetables too-even tomatoes and peppers with the proper support.