From our February 2018 issue, the ultimate hydro report.
Growing crops using hydroponic growing methods is not a new concept by any stretch of the imagination. The origins of “urban farming” that we hear of today have long and deep-reaching roots emerging from as far back as the ancient Hanging Gardens of Babylon and the pre-Columbian Aztec empire.
Cannabis plants can thrive in hydroponics (Greek for “growing with water”). Most cannabis strains take to water-based growing systems like a duck does to water. Marijuana plants are heavier-feeding plants from both a water and nutrient perspective, so the more water and nutrients they take up in a healthy growing environment, the bigger, heavier and stickier they can get.
Most of the root growth and nutrient-solution absorption by cannabis plants occur directly in the aerated nutrient solution rather than in the medium or substrate. A nutrient solution, in hydroponic terms, is composed of clean or filtered water that has exacting ratios of the elements required by plants for a given growth phase that is maintained at the correct temperature and pH level (the balance of acidity to alkalinity).
On the flipside, think about the aerial environment of plants at the canopy level. When temperature, humidity, carbon dioxide and air exchange are met at optimal levels, buds grow big and healthy faster. Plants live in two very different worlds at the same time: the aerial environment and the root environment. Growers have a tendency to think mostly about what they can see, but it’s important to think about and understand what’s going on down below in the root zone.
A well-aerated hydroponic nutrient solution (from air pumps or recirculation pumps) contains higher levels of oxygen than can be found in soil conditions. Roots love oxygen, and the difference when enough is supplied can be profound; an oxygenating nutrient solution supercharges the root zone, making nutrient and water absorption incredibly efficient for plants.
The exacting and optimal conditions created in the root zone via well-designed and constructed hydro systems provide uninterrupted nutrient and water absorption. One of the biggest advantages that hydroponics has in accelerating growth and development is the stability, consistency and replicable nature of the water, mineral and oxygen levels in the root zone.
Healthy cannabis crops can absorb lots of water when grown large or in high densities during the peak bloom cycle. If you aren’t growing in a closed hydroponic system, it’s a good bet that you’re losing a tremendous amount of the water through evaporation from the growing media in your beds, containers or planting holes.
Most experienced growers who have grown in both hydro and soil/soilless growing methods will observe a near–50 percent reduction in the amount of water they apply for topping up reservoirs compared with irrigation of beds or containers filled with growing media.
Another common observation by experienced growers using supercharged water-culture systems is that significantly lower fertilizer levels are required to support healthy and heavy-yielding crops of buds. Since the conditions for nutrient absorption and transport in the plant are optimal in these types of systems, there is no need to “force feed” plants as there is with soil and soilless conditions; hydroponic crops can take up as much as they desire at any time, uninterrupted.
You don’t have to be a master horticulturalist to reap the benefits and rewards of growing cannabis with water culture. As a matter of fact, there are plenty of first-time indoor growers who choose hydroponics and enjoy continued success with ease.
There are almost as many system types as there are growers using them. Proven and well-built hydroponic systems are widely available at reasonable prices. Consider that a hydroponic system is a small investment relative to the value of the crop you stand to harvest over several years. Typically, there’s little to replace or throw away between crops with water-culture systems. Simply clean out tubs, scrub with a little bleach and water, rinse and plant again—this can all be done on the same day of your harvest, making your growing space more productive with potentially more crops per year, requiring less work and replacement costs.
Hydroponic growing media like grow stones, lava rock or clay pebbles can be reused nearly indefinitely. Remove any old root debris and rinse well in a mild nutrient solution at the correct pH, and they are ready to fill into net pots or containers again. Rockwool is a popular hydroponic growing media, although it is best used as a propagation media where a relatively small amount is required, rather than a final growing media, because it is costly to replace and difficult to dispose of in a conscientious manner.
Basics: A small amount of growing media supports plants placed on a lid above a depth of a sturdy container holding well-aerated nutrient solution. Roots grow into the depth of solution and feed freely. If recirculated, a water pump draws the nutrient solution through the root zone and recirculates through connected pods or modules (containers with lids).
Advantages: There are lots of them for this quintessential hydro system—basically all of the advantages we discuss in this article. It can be built cheaply and easily as a DIY system from available parts, and, for serious growers, there are complete and proven professional systems available.
Limitations and challenges: Keeping the modules from overheating past 75°F under artificial grow lighting before the crop develops enough leaves to shade the lids is something to watch out for, although there are plenty of solutions to this common problem.
Basics: Containers or grow cubes sit in a specially made “flood table” with grooved bottoms and raised sides. The majority of the plant roots will grow between the media and the flood-table surface. Nutrient solution is pumped into the table to a depth that will partially submerge the containers or cubes on a timed cycle. When the pump shuts off, the solution is drained back into the reservoir, ready for the next recirculation cycle.
Advantages: This system is reliable and offers a good level of moisture-level control in the root zone; yields can be very good with high planting densities as with SOG (sea of green) high-density cropping methods.
Limitations and challenges: It’s best for smaller-stature plants as the table height above the reservoir and average ceiling heights may limit growth space when used with high-output lighting. Flood tables can be bulky and cumbersome to ship or move around, and they take up a lot of space in the growing area.
Basics: A shallow depth of nutrient solution moves from a slightly elevated end on the inside of a supportive channel or tube across the entire length of the bottom then out through a drain on the opposite end of the channel or tube. The nutrient solution is recirculated continuously in NFT systems.
Advantages: The system is highly scalable, and it allows for easy perpetual harvesting cycles. It’s possible to harvest 26 times per year using multiple stages of NFT cropping with high plant densities in a relatively small area. The system is very automation- and labor-friendly.
Limitations and challenges: It’s best suited to smaller-stature plants in high densities. Power failures or clogged lines can be disastrous, although they are entirely preventable with the proper setup.
Basics: Plastic “spaghetti” lines deliver water and nutrients via a water pump from a reservoir, either recirculating or as a drain to waste applications to pots, cubes or buckets. There are many variations on these types of setups, and they use common irrigation emitters and parts, which make them popular with the DIY set.
Advantages: They’re highly flexible, and a variety of growing media can be used or may be adapted for water culture, i.e., bucket systems. They’re great for reliable and effective low-cost hydroponics with a professional system. Highly precise moisture management is attainable.
Limitations and challenges: They tend to be maintenance-intensive, as emitters and spaghetti lines are prone to clogging over time with “salt” buildup, even with proper filtration equipment.
Basics: In a sense, these use fuel-injected and supercharged hydroponics. Plants can grow incredibly fast in a fine-tuned and well-maintained aeroponics system, which uses pressurized sprayers to deliver a fine mist or wide spray of fine nutrient-solution droplets to bare-rooted plants supported by a lid covering the internal root chamber. The large surface area of the nutrient mist creates dramatic oxygen levels with high levels of nutrient penetration directly into plant roots.
Advantages: Incredible growth rates and crop development are achievable with aeroponics. Aeroponics are often a first choice for hydroponic growers interested in rooting cuttings for transplant into other systems.
Limitations and challenges: Aeroponics can be unforgiving with errors (clogged sprayers, etc.). This system is best reserved for high plant densities with fast crop turnaround times; it’s built for speed.
Having good-quality water out of the tap or well is a huge bonus for growing with hydroponics because your water condition counts. Impurities in water can react with the ingredients in your nutrient solution, which will hurt the performance of your plants. Water filtration for hydroponics is widely available with lots of selection for different-size applications—with reasonable prices. Reverse-osmosis filtration is optimal, although two-stage particulate filters that capture sediment and chlorine can do much to improve water quality too.
For smaller systems, water can be managed with buckets from the source, while for larger setups you’ll want to be able to access your water supply for the garden within the growing area.
Hydroponic growing performs great indoors or out. Sturdier and heavier systems are preferred for the outdoors when there is no greenhouse or shade structure. A strong wind can pick up a flood table and send it sailing if it’s not properly anchored into position. Shade structures are a good idea outdoors—anything that allows you to use different degrees of shading throughout the season can help prevent your nutrient solution from overheating while also providing some stealth for cannabis crops. In some situations, a water chiller may be required.
While the methods described here are not exclusive to hydroponic growing, they are most easily utilized for maximum benefit when cultivating buds with hydroponics.
The fundamental principle at work in capturing water for reuse in growing systems is that plants transpire almost all of the water they take up through their roots as water vapor from tiny openings in the leaves. It’s the water that keeps plants upright—they don’t have any bones!
All of this water has to go somewhere. Indoors or in greenhouses, it is either vented away by fans or captured and drained away as condensate by air conditioners and dehumidification equipment. Wait, stop right there!
The water that plants transpire is pure and “alive,” as it has been filtered by the plants themselves. Collecting condensate from growroom air conditioners and dehumidifiers can drastically reduce the amount of tap water you will need to filter each time you top up your reservoir.
As long as the condensate is discharged through clean appliances and is not exposed to strong light or organic debris, it’s an excellent source of water for your growroom. As a precaution, there are also compact water-treatment systems designed specifically for the purpose of filtering condensate in the growroom or greenhouse—for example, particulate-filtration and UV-sterilization systems.
You may have heard that cleanliness is next to godliness. This certainly holds true in hydroponics. The solution inside your hydro system can be managed for an entire crop—with proper management, there is no need to dump and refill large volumes of solution. Experienced hydro growers do not add unrefined organic ingredients, and they typically stick with mineral solutions—although there are a few certified organic formulas that work very well in water-culture systems. Adding organic ingredients into a highly aerated solution with no growing media can be like throwing diesel fuel into a camp fire. It’s best avoided. Otherwise, you are looking at an unconfined explosion of microbial growth and organic residues that attract and harbor unwanted pathogens.
The rule of thumb that most hydro growers who crop buds follow is not to let the nutrient solution get warmer than 72°F. However, this doesn’t mean that you can’t.
While lower reservoir temperatures help to prevent unwanted microbial growth and keep higher DO (dissolved oxygen) levels, lower root-zone temperatures slow a plant’s metabolism and may not always be practical to achieve—for example, when growing in a greenhouse during the hot months or under lights with cooling fans blowing in outside air.
The solution: Keep organic-based fertilizers or nutrient additives out of your solution when you are operating a hydroponic system that will average over 72°F. Add hypochlorous acid (a special plant-friendly “bleach”), following the manufacturer’s directions. It’s usually best to apply lower dosage rates more often—for example, every three days. Hypochlorous acid is effective in keeping microbial populations in your hydroponic system low when temperatures are warm. Warm temperatures, microbes and organic materials, when combined together, are a recipe for trouble in most hydroponic setups.
Having a true water-culture hydroponic system that can consistently deliver good yields while operating with organic nutrients can be a reality, even for novice hydro bud gardeners.
Historically, this was like skating on thin ice: It’s doable, but risky. That’s because growers made their own teas or used other less-refined or rawer organic ingredients that were prone to unpredictable biological reactions in a highly aerated root environment.
The trick for successful and productive organic hydroponics is to use only highly refined organic nutrient solutions that are intended (and tested) for use in recirculating water culture. For example, five-stage fermented colloidal molasses nutrient bases have proven to be highly effective, and there are other organic complete-nutrient kits perfect for hydro cannabis now available.
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