In case you havn't read this article yet from Urban Garden issue 10
ADVANCED WATER CULTURE TECHNIQUES
One aspect of hydroponics that receives much attention from growers of all abilities is deep water culture aka DWC. Everest quizzes water culture expert, Daniel Wilson from Current Culture H2O, and discovers some great tips on running these productive hydroponic systems.
Of all the hydroponic growing media you can use water is cheap and the easiest to obtain. Water can be filtered, typically with an RO machine, and sterilized with UV or Ozone to create a clean and consistent substrate tailored to your growing requirements. Many hydroponic growers already understand the virtues of using, and more importantly reusing, water in hydroponic systems. So, why not go the whole hog, throw away your rock wool/soil/coco/clay pebbles and use water culture?!
What is Water Culture?
Deep water culture (DWC) – At its essence, a DWC system is made up of a container, lid and net pot. The container holds the nutrient solution (typically 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. Shallow water culture (SWC) is based on the same principle but, yes you’ve guessed it, uses a lower volume of water.
Single vs. Recirculating
Single stand-alone systems are fairly cheap to buy and even more popular for DIY enthusiasts. Modular DWC systems, in which many 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. Each has inherent issues. Stand-alone systems can be inconvenient to work with, while recirculating systems can spread problematic root diseases very quickly. The key is to operate the chosen water culture system properly, and you’ll be sure to get explosive results. Once you play around with DWC, you’ll most likely wish your system was modular and recirculating.
Q: Ok, lets start with the basics; what types of nutrients and additives work in DWC?
A: In my experience, pure synthetics of the highest solubility tend to work best. Especially formulations with well-balanced mineral ratios as well as being balanced on a molecular level. This tends to translate to a more pH stable nutrient solution that stays viable for longer periods of time.
Q: Where do you stand when it comes to Beneficial Biology in DWC systems?
A: There’s a bit of a fork in the road philosophically when it comes to“bennies” or no “bennies”. In my experiences both tend to work but I lean towards more of a sterile aqueous root zone. It is possible to use a more carbon-based substrate for a plant’s root crown cultivation. It’s this beneficial habitat that could harbor and allow colonization of a plant’s mutualistic organisms. The solution itself has little potential for colonization of anything other than bacteria, which while useful, don’t offer the benefits of fungi’s, which share a more direct relationship with the roots themselves.
Q: Are there any specific pH and EC requirements you recommend?
A: Depending on the nutrient, working with a pH between 5.5–6.5 works fine. If you want to be more specific 6.0–6.3 for veg, and 5.7–5.9 for flower. It’s in these pH ranges that the minerals most needed for the respective plant cycles are most available. With regards to EC, I generally recommend 50–75% of a nutrient manufacturers directed dosage for best results. Remember that 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 growers change-out the nutrient solution? Are there signs they should look out for?
A: Depending on the type of nutrients, a 14–21 day change out schedule is typical. When plants are growing vigorously they can turn the nutrients over several times in that time frame. This is essentially “changing the nutes” by displacement from the top-off reservoir. If the nutes begin to fluctuate in pH or become murky, or if plants begin reducing nutrient usage this is usually a good time to purge the reservoir and mix a fresh batch.
Q: What is the ideal water temperature for DWC systems?
A: We’ve observed that no matter the ambient air temperature, plant roots tend to do best at 62–68°F (17–20°C). Above 72°F (21°C) the solutions dissolved oxygen (DO) holding potential quickly diminishes and below 60°F (16°C) plants tend to slow their metabolism in response to what is perceived as changing seasons. This said, growers could aid in fruit/flower ripening by reducing water temps toward the end of the reproductive cycle. Being able to dial in each zone of the plant (Leaf/Root) specifically often leads to an amplification of plant productivity.
Q: Speaking about DO, what is the best practice for monitoring and maintaining DO levels?
A: Keep nutrients cool and ppm’s at a modest level to ensure good DO saturation. Surface aeration and the implementation of air pumps and diffusers is an easy way to keep the solution agitated and moving. Manual as well as digital meters can be useful for those more meticulous souls. If you go digital buy high end as the budget meters (which still run several hundred dollars) are typically unreliable instruments in a pretty plastic housing.
Q: Can you run through your recommendations for propagating plants destined for DWC?
A: Establishing cuttings with an aeroponic cloner using 1/8th strength nutrients is ideal, preferably under mixed spectrum T-5 lighting. Propagating bare root plants suits DWC best. This offers an easier transition to water culture given there is no wicking substrate (rock wool, Sure To Grow) to hold excess moisture too close to the root crown.
Q: Is there an ideal water level to be maintained in the reservoir?
A: Start with the bare root submersed to the base of the rooted stalk, being sure to not submerse the stem or stalk tissue so as to avoid water logging. If using a wicking substrate, 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: What are the potentialities for plant steering using water level / amount of root zone exposed to the air?
A: With water as their growing media, growers can tailor nutrient solution parameters more specifically. Provoking plant responses such as essential oil production, fruiting and flowering are better manipulated when the substrate can be dialed in. For example, higher exposure of the root zone to atmospheric oxygen can help trigger a plant to increase oil production as a means to conserve water, and can also apply mild root stresses that are often interpreted by the plant as reproductive cues. While higher water levels can cause plants to focus more energy on vegetative production, particularly fan leaves, which in turn speeds transpiration and photosynthetic potential.
Q: Are there any specific pests or pitfalls DWC growers should watch out for?
A: Root diseases no doubt, Pythium, Fusarium, etc. These types of problems are most evident in water culture given the roots high profile, but are also typically found in most hydro methods currently practiced. In our experiences we’ve observed that once the variable causing the problem is removed (warm water, too high an EC, sludging inputs, etc.), it’s completely likely the plants will recover. In other words, root disease is not a death sentence, but a symptom of a problem needing to be addressed.
Q: I have heard from a few DWC growers that veg times can be significantly reduced, is this true?
A: Growers will need to make that call, but when dialed-in there is no faster way to grow plants—hydroponically or otherwise. A well-hydrated plant typically grows more quickly which will inevitably create shorter veg times and still achieve a premeditated harvestable plant size.
Q: Is DWC suitable for longer-term plants, such as donor plants? Commercially DWC is only used for lettuce and short-cycle plants, not for annuals.
A: Water culture is still a relatively new hydroponics method. Though first introduced in the 1930s by professor Gericke at UC Berkley, using water as a primary growth medium is still seen as somewhat impractical by commercial farmers. Due to the need to keep water conditions cool, it’s caused the bottom line to operate large-scale water culture facilities to be cost prohibitive.
Though with the recent improvements in cooling technology and increased efficiencies, I think we are likely to see a move toward water culture as a viable alternative to the current carbon substrate-based approaches presently being used for the growth of annual vegetables.
Especially as farmers discover the reduced volume of fertilizer inputs and the conservation of precious water that are key to water culture’s allure. This is an exciting time for water culture as what has been considered a black art is now emerging as a legitimate means of cultivating a variety of crops.
