Nutrients in Cannabis: DIY vs. Pre-Bottled Formulas
Cannabis and hemp have unique nutrient needs just like any other conventional crop. Much like their traditional counterparts, these needs also vary by stage of growth, from seed to nug or hemp shiv. Of course, these, too, depend on the grower and their methods and goals. Obviously, hydro growers will use fertilizers that are different from soil growers. Someone growing for extracts will likely use a different formulation than someone growing only for smokable flowers, etc. This wide range has driven farmers to search for the perfect formula for their growth. In turn, this demand has fueled nutrient companies to better service growers by providing them with formulas believed to work well in their operations. The caveat is that these companies are servicing an entire sector, so it’s hard to provide a custom blend for everyone. What works well for one facility may not work for another. Obviously, some tweaks can be made to make it work, but often, this is to the detriment of both the nutrient company and its customers. All this is to say that we are now seeing a surge in interest on behalf of cannabis cultivators in making their own recipes, both as a way to fine-tune their plant needs and a way to save money.
Nutrient Needs by Stage
Seed/Seedling
Depending on the method utilized, typically seeds are only given water—and usually non-mineralized at that. Seeds have very little nutrient needs, and excess can burn them or even stunt growth.
Vegetative Cycle
The vegetative part of the cycle requires heavy nitrogen feeding the most. Obviously, there are other macro and micronutrients, but nitrogen is the most important to really give them that green growth and help them stretch. Calcium is another important element at this stage, as it ensures that branches are dense and not hollow. This also helps the plant stay upright and increase yields.
Flowering
Flowering can get complex, but generally speaking, you want to start giving the plant more phosphorus and potassium at this stage. Silica and zinc are some others as well that really help the buds stay strong and fight off pest pressures that increase closer to harvest.
Varying Nutrient Needs by Cultivar
It’s been noted by many cannabis cultivators that different strains require differing nutrient levels as well. This may seem obvious when you see the size differences in a mature crop, but even cultivars similar in stature or even terpene profile can be widely different. Adjustments are complicated both by irrigation and facility logistics as well as timing. Irrigation is usually connected by zones, but typically, zones are large enough that they incorporate multiple strains (or tables). Not always, as it depends on the cultivator’s layout, but larger operations especially almost always optimize for space rather than plant needs. What this means is that if there are multiple strains in a zone, they will all receive the same formula despite each having different needs. To take this a step further, many cultivators even use the same formula and vats for an entire room and simply adjust the volume of fertigation for each cultivar rather than the compound makeup. How much of a difference this makes in terms of crop yield and quality is still up for debate when you’re at this scale. But one thing’s for certain: those who do mix their own nutrients are more able to dial in their grow and save money. Why would you not want that?
Varying Recipes by Medium Type
Most hydroponic growers utilize liquid fertilizer, usually in the form of “salts,” to feed their crop. Soil growers, on the other hand, vary widely between compost teas, liquids, powders, and top-dresses. One thing to note about soil is that fertilizer and nutrients are often pre-loaded or even mixed and incorporated into soil prior to planting. Soil growing is all about soil health and trusting that the soil will take care of the plants. Hydro growing is essentially skipping a step and just going straight to taking care of the plants directly. Each approach has pros and cons. Here’s an example recipe from each type:
Soil Recipe:
Ingredients:
- Blood meal (12-0-0): 2 cups (nitrogen source for vegetative growth)
- Bone meal (3-15-0): 3 cups (phosphorus and calcium for root and flower development)
- Kelp meal (1-0-2): 1 cup (potassium, micronutrients, and growth hormones)
- Alfalfa meal (2-0-2): 1 cup (nitrogen, potassium, and triacontanol for growth stimulation)
- Rock phosphate: 1 cup (long-term phosphorus and calcium)
- Dolomite lime: 1/2 cup (calcium, magnesium, and pH buffer)
- Worm castings: 2 cups (micronutrients, microbial activity, and soil conditioner)
- Crab shell meal: 1/2 cup (calcium, chitin, and fungal resistance)
Equipment:
- Large mixing bucket or tarp
- Measuring cups
- Gloves
- Airtight storage container
Instructions:
- In a well-ventilated area, combine all ingredients in a bucket or on a tarp
- Mix thoroughly with a shovel or gloved hands to ensure even distribution
- Store in an airtight container in a cool, dry place to preserve nutrient potency
- Label with the date mixed (use within 6–12 months)
Application:
Soil Preparation (Before Planting)
- Mix 1/2 cup of amendment per gallon of soil (e.g., 3–4 cups for a 7-gallon pot)
- Combine with high-quality organic potting soil or compost (30% compost, 70% soil recommended)
- Let soil “cook” for 2–4 weeks in a covered bin to activate microbial activity, keeping it moist but not soggy
Top-Dressing (During Growth):
- Vegetative Stage: Apply 1–2 tablespoons per gallon of soil every 2–3 weeks. Scratch lightly into the top 1–2 inches and water thoroughly. Supports nitrogen needs (approximately NPK 5-4-2)
- Flowering Stage: Apply 1 tablespoon per gallon every 3–4 weeks, supplemented with 1 teaspoon of kelp meal per plant for extra potassium. Reduce to every 4–6 weeks in late flowering
Watering: Use dechlorinated water, maintaining soil pH at 6.0–6.8 (test with a soil pH meter)
Caution: Avoid over-application to prevent nutrient lockout. Flush with water if plants show stress.
Hydro Recipe:
Ingredients:
- Epsom salt (magnesium sulfate): 1 tablespoon (source of magnesium and sulfur)
- Potassium sulfate: 1.5 teaspoons (source of potassium and sulfur)
- Monopotassium phosphate: 1 teaspoon (source of phosphorus and potassium)
- Fish emulsion (5-1-1): 2 tablespoons (nitrogen source and micronutrients)
- Liquid kelp extract: 1 tablespoon (micronutrients, trace elements, and growth hormones)
- Molasses (unsulfured): 1 teaspoon (carbohydrates for microbial activity and micronutrients)
- Water: 1 gallon (use dechlorinated or rainwater for best results)
Equipment:
- 1-gallon jug or bucket
- Measuring spoons
- Stirring utensils
Instructions:
- Fill a 1-gallon jug with dechlorinated water (let tap water sit for 24 hours or use a de-chlorinator)
- Add Epsom salt, potassium sulfate, and monopotassium phosphate. Stir until fully dissolved
- Add fish emulsion, liquid kelp extract, and molasses. Mix thoroughly
- Let the mixture sit for 1–2 hours to stabilize, stirring occasionally
- Store in a cool, dark place and use within 1–2 weeks to prevent fermentation
Application:
- Vegetative Stage: Dilute 1 cup of fertilizer mix per gallon of water. Apply every 7–10 days, ensuring soil or medium is moist before feeding. Provides a nitrogen-heavy boost (approximately NPK 5-2-3)
- Flowering Stage: Dilute 3/4 cup per gallon of water and supplement with an additional 1/2 teaspoon of potassium sulfate per gallon to boost potassium (approximately NPK 3-2-5). Apply every 10–14 days, reducing frequency as buds mature
- pH Check: Adjust the final solution to pH 6.0–6.5 for soil or 5.5–6.0 for hydroponics using pH up/down solutions
Caution: Test on one plant first. Flush with plain water if signs of nutrient burn (yellowing tips) appear.
Pros and Cons of DIY vs. Pre-Bottled
As previously mentioned, there’s no right or wrong way to grow. While going DIY ultimately allows for the highest optimization and can save money on ingredients, some larger farms may find it easier to purchase premixed nutrients from companies such as Athena. Generally speaking, these companies use high-quality inputs and have years of experience to back the chemistry behind their products. This comes in handy for those new to cannabis or perhaps those with less of a chemistry knack who may have specialties in other areas of growing. Labor is another consideration, as mixing these formulas is no small feat. Depending on the size of the grow rooms and the facility, more generally, this mixing could take up an entire day that could have been diverted to plant work or other tasks. Again, there’s no right or wrong way, so long as the company or brand is aware of its mission and tailors their operations to it.
Further reading
Hemp in Animal Feed: A Sustainable Solution for Livestock Nutrition
Genetics in Cannabis: Similarities and differences to conventional crops
Cannabis Physiology: Growth, Cultivation Techniques, and Evolution Explained
Cannabis: A Global Overview of Regions, Restrictions, and Popular Varieties
