Growing marijuana hydroponically gives indoor growers an unprecedented amount of environmental control. It allows for careful manipulation light and temperature, as would be the case with a soil-based indoor grow, with the addition of nutrients, pH, EC, and more. Those who are new to hydroponic growing can read on to find out everything they need to know about creating a perfect environment for their hydro setups.
Hydroponic growers need to pay careful attention to nutrient levels throughout their plant’s life cycles. Unlike the liquid plant foods used in soil-based grows, hydroponic nutrient solutions contain no organic materials. They’re specifically formulated for hydroponic setups.
A good nutrient solution should have chelated mineral nutrients that are easy to absorb. Since the plants won’t be absorbing any nutrients from the soil, an ideal hydroponic nutrient solution will also contain significant amounts of micro-nutrients.
Growers who are new to using hydroponic setups are often tempted to supplement their nutrient solutions with organic materials like guano, worm castings, fish emulsion, and blood meal. That’s a mistake for two reasons.
First, adding organic matter to a hydroponic system, even in liquid form, can introduce harmful bacteria. Since hydroponically grown marijuana plants don’t have natural defenses built up against these bacteria, the results can be disastrous.
The second reason it’s never a good idea to apply organic fertilizers or supplements to a hydroponic system is that these manufactured ecosystems don’t contain the same microorganisms found in soil. In an outdoor grow or an indoor soil-based grow, the soil contains beneficial bacteria, fungi, and nematodes capable of breaking down organic materials and releasing them into the surrounding environment. When these microorganisms are absent from the environment, the nutrients found in organic materials can’t be broken down, so they won’t do the plants any good.
Like soil-based fertilizers, hydroponic nutrient solutions need to have a correct Nitrogen-Phosphorous-Potassium (NPK) ratio. These three macronutrients are essential almost all plants, but ideal concentrations vary throughout the plant’s life cycles.
In the vegetative stage, the ideal NPK ratio for hydroponic nutrient solutions is 7-5-5. During the flowering stage, it’s 3-10-10. Other nutrients hydroponic growers should look for include Sulfur, Magnesium, Iron, and Calcium.
Hydroponic setups that use soft water may also require additional micronutrients or minerals. Check the water supply to the grow room before buying hydroponic nutrient solutions to see if it already contains trace amounts of minerals frequently found in hard water.
The term pH refers to the rate of positive and negative charges in water ions. Water with a pH under seven is considered acidic, while water with a pH over seven is alkaline. A nutrient mix with a pH of exactly seven would be neutral.
The pH scale works on a consideration of 10, meaning that a solution with a pH of 6 is ten times more acidic than a neutral solution. To make matters even more complicated, different materials can raise or lower the pH in water and nutrient solutions, which can impact the ability of marijuana plants to grow and thrive. Hydroponic growers need to monitor pH on a regular basis to ensure that it remains at an optimal level.
The ideal pH for hydroponically grown marijuana plants is between 5.5 and 5.8, but growers have some wiggle room. A nutrient solution with a pH reading as low as 5.3 or as high as 6.5 can still produce a high-quality crop, especially if growers take note of the discrepancy and alter the solution accordingly.
Plants in a hydroponic setup start to suffer when the pH drops below 4.5 or rises above 8.0. At this point, the plants won’t be able to absorb nutrients efficiently. If the pH gets any further outside of these outer limits, it can cause permanent damage to the roots, decreasing yields, or even killing the plants.
Growers should measure and note the pH of their liquid nutrients before introducing them to the system. Aim for a liquid nutrient pH of 5.5 or higher to keep the nutrient solution within an optimal range.
It’s best to take action as soon as the pH reaches 5 or below. At this point, the plants may already be starting to show symptoms of toxicity. The easiest way to raise the pH is to mix caustic potash into the water. Growers should exercise caution and apply only a little of it at a time, though. A little bit goes a long way.
When the nutrient solution reaches a pH of 6.5 or higher, it can cause plants to become deficient in calcium, iron, and phosphorous even if these elements are present in the solution. The best way to tackle high pH in vegetative plants is to add diluted nitric acid to the nutrient mix. For plants that are already in the flowering stage, look for diluted phosphoric acid instead. These products are sometimes sold under the labels pH-growth and pH-flowering.
Growers who use rockwool in their hydroponic setups should note that it is a naturally alkaline substance. It needs to be soaked for a full day before it can be used safely as a growing medium. Rockwool slabs can also release alkaline substances into water over time, so growers should be conscientious about measuring the pH levels in their hydroponic setups and make adjustments as needed.
Growers who use tap water in their hydroponic setups also need to exercise some extra caution. Tap water is usually slightly alkaline, and marijuana plants prefer a slightly acidic environment. Again, just test the nutrient solution frequently and add amendments specifically designed for hydroponic systems as needed.
EC, short for Electric Conductivity, is a measurement of dissolved salts or nutrients. Dissolved nutrients can also be measured on a scale of total dissolved solids (TDS). EC and TDS values can be tricky to determine, as they vary substantially depending on everything from the plant size to the amount of water the setup uses and even how much light the plants receive.
EC can be measured using a specialized tool referred to as a TDS meter. TDS meters measure concentrations of nutrients or minerals in parts per million (PPM), but they don’t just measure nutrient levels. Ordinary tap water typically has a TDS between 200 and 400ppm, while distilled water has a TDS of 0ppm. Not all TDS meters offer both EC and TDS measurements, so make sure to find one that does.
It may be frustrating, but optimizing EC takes some trial and error. Some growers prefer more concentrated nutrient solutions, while others like them diluted. Most liquid nutrients purchased from garden and grow stores have a TDS value of between 600 and 750ppm or an EC of between 1.2 and 1.5 mS.
Once growers determine the current and optimal EC levels for their setups, they can maintain it by changing the frequency of their drip feedings. More frequent feeding increases TDS. In other words, the more often growers drip, the higher the EC will be.
Rinsing is essential for maintaining not just healthy EC levels, but also optimal pH. To perform this task, growers will need a TDS meter, a pH meter, a measuring cup, and a syringe.
To get started, just remove some water from the growing medium and measure its pH and TDS. Growers working with especially large setups may want to choose one or two test plots to observe throughout the season.
Whether they’re testing each plot or just a few test plots, growers should take measurements for several syringes taken from different points in the system first, noting down pH and TDS levels. Next, mix them all together and note down the total. This should give growers a better idea of how the nutrients are flowing through and interacting with their plants’ root systems and give them the chance to adjust them as needed.
If the TDS is high, or the pH is low, just add tap water until the measurements return to optimal levels. Most growers aim for around pH 5.5 and 250 TDS, although every setup is a little different. Expert growers who already know their way around hydroponic setups can usually give themselves more leeway, since they know their plants better. Those who are new to hydroponic growing should try to keep their pH and EC levels as close as possible to optimal levels.
Monitoring and controlling a hydroponic system comes with some extra challenges, but growers who are careful about maintaining optimal pH, EC, and nutrient levels will find that the extra work pays off. Although these factors all play an essential role in determining plant health, it’s equally important for growers to continue paying attention to lighting schedules, carbon monoxide levels, temperature, and humidity in their grow rooms. It takes some time to get all of these elements exactly right, but in the end, growers will find that they wind up with healthier plants and heftier yields. It’s well worth the effort.