By creating cannabis fertilizers from scratch, commercial growers can decrease their operating costs and enjoy the flexibility of customizing their own nutrient recipes.
But growers that make the jump from buying bottled hydroponic nutrients to mixing their own fertilizer should be mindful of factors that could heavily influence the success of their feeding program.
Mistakes in the fertilizer mixing room could quickly translate into expensive plant problems once these oversights manifest themselves in the crop.
Growers looking to ditch their ready-to-use cannabis fertilizers for in-house nutrient programs should keep the following five tips in mind to maximize their chances for success:
Start Clean
Growers using raw water with high levels of undesirable minerals will need to treat their water before mixing it with fertilizer and sending it out to the crop. High levels of bicarbonates, chlorides, and sodium are some of the most common reasons that growers turn to reverse osmosis (RO) to purify their raw water.
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In recirculating systems, these can build up to problematic levels, so the RO process strips all minerals from the water, providing the grower with a blank canvas from which to create their nutrient recipe.
But if the raw water does not contain alarming levels of certain minerals and the grower uses a run-to-waste system, RO treatment may not be necessary. Many of the same minerals stripped away during the RO process are later reintroduced through fertilizer.
If your raw water is within these acceptable ranges, you may be able to skip the expense of an RO system:
- pH: 5-8
- Alkalinity: <200ppm CaCO3
- EC: <1.0
- Calcium: <150ppm
- Magnesium: <75ppm
- Sulfates/Sulphur: <50ppm
- Iron: <1ppm
- Manganese: <.50
- Boron: <.50
- Sodium: <30
- Chlorides: <30
- Fluoride: <1ppm
- Heavy metals: Non-detectable
Use Greenhouse-Grade Minerals
Minerals that haven’t been adequately refined may contain elevated levels of heavy metals, which are undesirable in cannabis. As accumulator crops, cannabis and hemp will take up and store heavy metals that are present in the soil or fertilizer.
Most regulatory programs requiring product testing have stringent cutoffs for acceptable levels of heavy metals in the final analysis of dry flower and extracted products. A failed test can mean an unsaleable crop.
Cheap fertilizer ingredients may be insoluble or contain unwanted impurities that can put your crop at risk. Only use greenhouse-grade or technical-grade fertilizer minerals to avoid problems when it comes time to sell your crop.
Avoid Excess Phosphorus
A popular myth among cannabis growers is that the crop requires high phosphorus levels to jump-start the flowering process and guarantee huge buds. This is simply not true.
While mineral ratios vary between vegetative and flowering growth, the required phosphorus levels don’t fluctuate much. Researchers that have delved into this topic agree that cannabis and hemp won’t benefit from more than 50 ppm of phosphorus during flowering, with about 30 ppm being optimum.
Higher phosphorus levels in your cannabis fertilizers likely won’t result in larger flowers, but it could result in compatibility issues with micronutrients. Furthermore, the phosphorus that the plant doesn’t store or consume heads directly down the drain, along with the grower’s money.
Algal blooms in lakes and waterways are caused by excess phosphorus in water runoff, which is another reason to tighten up the cannabis industry’s love affair with phosphorus.
Be Careful With Additives
Although there are only 17 nutrients that are essential for plant growth, there are just as many (or probably more) fertilizer additives on the market that claim to boost the health and productivity of cannabis crops.
Fulvic acid, humic acid, silica, organic supplements, biostimulants, resin boosters, and carbo-loading fertilizers are just a few of the more popular products that can be added to an in-house fertilizer regime. There is increasing research to back up the efficacies of these products, but a lot is still anecdotal.
Be mindful of compatibility issues; at concentrated levels, some supplements could bind up other elements and make them unavailable to the plant. Organic-based supplements could lead to biofilm growth inside irrigation lines and drip stakes. Both scenarios will cause headaches for growers on a commercial scale, so it’s best to trial these products, and their compatibility, in an R&D setting before scaling up to the whole greenhouse.
Monitor Nutrient Uptake Using Plant Sap, Not Leaf Tissue Analysis
One of the most significant benefits of mixing your own fertilizer is the ability to adjust individual elements as the grower determines it’s necessary. Whether a mineral is to be increased or decreased should be based on the results of a plant sap analysis.
Plant sap is the mineral-rich fluid that flows throughout the xylem and phloem of the plant. By extracting and analyzing this sap in real-time, growers can make fertilizer adjustments before a nutritional imbalance results in economic damage to their crops.
Analyzing plant sap is more precise than leaf tissue analysis; the former allows the grower to see what’s happening today, whereas the latter shows what happened inside the plant weeks ago. Pairing plan sap analysis with an in-house fertilizer program is the best way to ensure a targeted and efficient crop nutrition program.
Growers looking to lower production costs and improve their feeding program’s precision are increasingly turning to in-house fertilizer recipes to grow their business. As long as the raw water is good, the fertilizer inputs are clean, and a nutrient monitoring program is in place, custom cannabis fertilizers can truly become a cultivation business’s recipe for success.
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5 Tips for Mixing Your Own Cannabis Fertilizer
Ryan Douglas is the founder of Ryan Douglas Cultivation, LLC, which helps new cannabis cultivation businesses come to market quickly and spend less money getting there. He is the author of From Seed to Success: How to Launch a Great Cannabis Cultivation Business in Record Time. See all author stories here.
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