The plants’ diet is one of the essential aspects of any cannabis crop. Giving your marijuana plants all the essential nutrients it needs is vital for it to not only producing top quality bud but also to withstand diseases and pests, and ensure a happy ending come harvest time.
Protecting plants from harvest-ruining pests and disease is essential and should be at the top of every growers list, because dank flower will never materialize if young crops fail before they are able to reach maturity and be harvested.
Cannabis plants draw hydrogen, carbon, and oxygen from their water source (whether it be natural or hydroponic) and the atmosphere (or indoor simulated atmosphere), but nutrients must be still obtained through the substrate and, to a lesser extent, from leaves.
Like many plants, cannabis planted in a substrate cannot develop properly without certain chemical elements furnished by the soil. Even many natural outdoor grows require additional nutrient supplementation from time to time, especially if not allowing for soil rejuvenation between grows.
Understanding Key Cannabis Macro & Micronutrients
Cannabis plants require three nutrients in large quantities. These macronutrients are nitrogen, phosphorus (P), and potassium (K), and they form the cornerstone of cannabis plant health. As such, these three nutrients usually feature front and center on fertilizer products in the form of an NPK ratio.
However, cannabis needs more than just three nutrients to survive and thrive. It also counts on secondary nutrients like calcium, magnesium, and sulfur to play vital roles in plant growth:
- Calcium is important for cell wall development can help reduce soil salinity, and improves water penetration when used as a soil amendment.
- Magnesium plays a key role in photosynthesis and carbohydrate metabolism, and also helps with the stabilization of plant cell walls.
- Sulfur is necessary for the formation of chlorophyll and the production of proteins, amino acids, enzymes, and vitamins, and protects plants against disease.
Plants also make use of several other nutrients in small quantities (micronutrients) that are nevertheless extremely important. These include boron, chlorine, copper, iron, manganese, molybdenum, and zinc. While these aren’t the main nutrients plants use for food, they still play very important roles in various aspects of plant health.
Essential Macronutrients (NPK) for Healthy Cannabis Plants
Growers have all kinds of secret macronutrient blends, preferences and specific quantities that they swear by. The below list is intended to highlight the most important macronutrients as well as why they are considered essential for a healthy grow.
Macronutrient #1: Nitrogen (N)
Nitrogen is mostly responsible for a cannabis plant’s growth during the vegetative stage of its life. It’s a crucial part of chlorophyll and without it, a plant can’t turn sunlight into energy and it won’t be able to grow.
Nitrogen is also part of amino acids that act as building blocks for proteins in a plant. Without the required proteins, your cannabis plants will be weak and frail. Nitrogen is also a part of ATP, which allows plant cells to control the use of energy.
Nitrogen is also necessary to create nucleic acid and a vital ingredient in DNA or RNA, and without it, cells won’t be able to grow and multiply.
Macronutrient #2: Phosphorus (P)
Phosphorus is an essential macro element, required for the success of all known life forms, including cannabis plants. Phosphorus is especially important for early-stage root development, stem strength, resistance to disease, nutrient uptake, flower formation, and yield. All aspects of cannabis growth and development are explicitly dependent on Phosphorus availability.
Phosphorus is important for producing large, healthy buds. The key role of this element is to help make nutrients available for the plant to uptake. These nutrients are used to build the structure of a plant as it grows from its roots to its flowers.
Without sufficient phosphorus, marijuana plants will show signs of undeveloped roots and might not even flower. Early signs of phosphorus deficiency show up as a purple hue in the veins of leaves.
Macronutrient #3: Potassium (K)
Potassium has several jobs that largely help control the systems that keep a plant healthy and growing. It plays a large role in osmoregulation, the passive regulation of water and salt concentrations in the plant. Potassium accomplishes this by controlling the opening and closing of the stomata—the pores in the leaves—which is how a plant exchanges CO2, H2O, and oxygen.
Potassium also triggers the production of ATP, which works to store energy produced in photosynthesis by creating glucose. This glucose is then used as energy for the plant as it grows. Without sufficient potassium, you will see weak plants starved for energy that appear burnt because they are unable to successfully regulate the exchange of CO2, H2O, and oxygen.
Essential Micronutrients for Healthy Cannabis Plants
The above mentioned macronutrients can be thought of as your meat, carb and veggies. The below listed micronutrients can be considered everything else that goes into making a tasty meal.
Micronutrient #1: Calcium
Calcium is responsible for keeping the structure of cell walls in a plant together. Without calcium, new growth won’t develop properly and the plant won’t function as it should. New growth will be stunted, leaves will curl, and rusty spots will show up on the plant.
Calcium can help reduce soil salinity and improves water penetration.
Micronutrient #2: Magnesium
Magnesium acts as the central molecule in chlorophyll and without it, plants aren’t able to generate the glucose from photosynthesis. No magnesium means no energy can be converted from sunlight.
Once magnesium has helped create glucose, it helps metabolize glucose to make it available for the plant to grow. Without sufficient magnesium, you will find yellowing leaves, with discoloration reaching the veins as well.
Micronutrient #3: Sulfur
Sulfur is necessary for the formation of chlorophyll and the production of proteins, amino acids, enzymes, and vitamins, and protects plants against disease.
When To Change Your Nutrient Mix Ratios
Marijuana plants require different nutrients at different stages of the life cycle. The life of a marijuana plant can be split into three main stages: Germination and rooting vegetative growth, and flowering.
Stage 1: Germination & Rooting
Germination usually takes place for around the first week of the plant’s lifetime. Depending on whether you are growing from seed or a cutting, this time may be more or less and nutrient needs will be lesser or greater. Growing from seed usually does not require any additional nutrients. Marijuana plants store nutrients in the seed husks, and so this tough outer layer serves as food for your seedling, giving it all the nutrients it needs to begin to grow
Stage 2: Vegetative Growth
Early in the cannabis life cycle, nutrient requirements are minimal. During the vegetative growth stage, your plant will require a good amount of nitrogen, as well as some phosphorus and potassium.
Throughout the growth cycle, this requirement can fluctuate significantly, so it is a good idea to vary your feeding regime depending on the age and size of your plant.
- Seedling Stage: It is commonly suggested, at least as a starting point, that a ratio of 2-1-2 for NPK is ideal.
- Early Vegetative Stage: When the plant is starting to look larger, around week 3 – 4, switch to a higher amount of nitrogen. The ratio 4-2-3 is suggested as a good balance.
- Mid Vegetative Stage: Around weeks 5 – 6, you can boost the nitrogen even more to give your plant the necessary energy to bush out. Go for something in the region of 10-5-7.
It’s important to remember: the ratios of these nutrients are far more important than the actual numbers. A mix of 8-4-6 or even 16-8-12 is both the same as 4-2-3 in terms of the relationship of one nutrient to the other, so the results will be largely the same.
As a general rule of thumb, during the vegetative stage, it’s good to keep phosphorus at around half that of nitrogen, and potassium at around half to two-thirds of the nitrogen. Nutrient requirements vary from one plant to another, so keep in tune with your plant’s needs and vary your feeding regime accordingly.
Stage 3: Flowering
As cannabis plants transition into flowering, macronutrient requirements swing in the opposite direction. That means switching to bloom base nutrients and adjusting the NPK ratio.
The flowering stage requires a significant increase in phosphorus, to give your plants the energy and resources to make nice, big, sticky buds. It can be a good idea to prepare your plants for the changeover from vegetative to flowering by feeding an equal mix of all nutrients for around a week.
Some farmers recommend a mix of 7-7-7 for this phase, but again the ratio is much more important than the numbers.
Once the plants start to flower, you need to switch to phosphorus as your main macronutrient. As a rough guide, you should aim to take nitrogen down to about half the amount of phosphorus, and potassium at around a half to two-thirds.
Recommended NPK mixes through the flowering period are:
- Early flowering: 5-10-7
- Mid flowering: 6-15-10
- Late flowering: 4-10-7
You will notice that in both the vegetative and flowering phases, potassium is maintained at around half to two-thirds of the level of the lead nutrient. Keeping close to this ratio will help you to avoid nutrient lockout and other problems associated with over or under-feeding your plants.
Which Nutrient Type Is Best? (Organic vs Synthetic)
Every living organism and this includes plants, requires nutrients. Nutrients (fertilizers) for growing cannabis can be inorganic (synthetically manufactured) or they can be organic. Simply spoken, growing organically means growing in soil with everything that is used for your grow is derived from living things. No synthetically made compounds, such as chemical salts or inorganic pesticides are used in the growing process.
Organic Nutrients Pros & Cons
Organic nutrients for marijuana are those types of nutrients that are made of or come from living “organic” sources like plants or animal waste. Some other substances, for example, mineral rock dust or gypsum can also be referred to as organic fertilizers.
Pros of Organic Grows
- There are several benefits of using organic nutrients for growing. As compared to chemical fertilizers, organic nutrients are normally slower releasing which means there is less of a chance for overfeeding and nutrient burn.
- Organic nutrients have a beneficial effect on microorganisms that are living in your soil, which in turn benefit your plants’ growth.
- Since organic nutrients are made from natural substances, they also tend to be renewable and ecologically sustainable.
- Beneficial organics, including growth-boosting microorganisms, stay in the soil, so there is less a chance of nutrient runoff and waste.
- When compared to feeding your plants with synthetic nutrients, when you grow organically it is for the most part about improving your soil and as a result, it improving the growth and health of your plants.
- Likewise, when you grow organically, your soil improves over time. Because of this, organic growing is highly attractive to outdoor growers, as it means you can reuse the same soil for many growing seasons.
Cons of Organic Grows
- Growing cannabis organically doesn’t just have benefits. As with almost everything, there are also some drawbacks.
- Organic nutrients usually take longer to be absorbed by the plant. The reason for this is that organic grows relies on microorganisms that break down nutrients and this is a process that takes some time.
- Your organic grow will in large parts rely on beneficial microorganisms that live in your soil. In colder climates, these microorganisms work slower breaking down nutrients. This means that organic nutrients can act slower and not as effective in colder temperatures.
- When compared to growing using synthetic fertilizers, where your growing medium can be pretty much sterile, organic substances in your soil can easier attract insects and pests.
- Last but not least, organic nutrients are usually more expensive than synthetic (chemical) cannabis nutrients.
Synthetic Nutrients Pros & Cons
Synthetic nutrients contain the minerals that are important for plant growth in a form instantly available to your plants. The three most essential minerals for growth are nitrogen, phosphate (P), and potassium (K). The nitrogen comes from an artificial nitrogen fixation process that’s called the Haber-Bosch process, which was invented in the first half of the 20th century. The phosphate and the potassium are extracted from minerals, with harmful impurities removed.
Pros of Synthetic Nutrients
- Synthetic nutrients are normally made with an exact ratio of specific nutrients. This means that the grower has more control over giving the precise amounts of nutrients that the plants require during their current growth stage. Nitrogen, for example, is most needed in the growing phase while later on, in flowering the cannabis plant would need less of it but needs more phosphorus.
- Being able to precisely add the right amount of nutrients can result in bigger yields and a higher THC content. It is worth noting that nutrient requirements can vary from strain to strain and phenotype to phenotype.
- Chemical nutrients are instantly available to your plants when you feed them. A rapid intake of minerals and other compounds makes it possible to impact your plants’ health immediately, say if you want to address a nutrient deficiency as fast as possible.
- Last but not least, synthetic plant fertilizers are available almost anywhere, and are normally much cheaper than their organic counterparts.
Cons of Synthetic Nutrients
- The fact that synthetic nutrients for growing cannabis are instantly available to your plants and can, at times, also be very concentrated increases the risk for overfeeding and nutrient burn. This can make synthetic fertilizers a tad more risky for less experienced growers who, at times, have a tendency to overfeed.
- Synthetic nutrients also cause salt build up over time in soil, degrading quality. With poor soil quality comes a higher chance for nutrient run-off, which results in nutrients being wasted, together with the harm this can cause to the environment. Poor soil also increases the likelihood of problems developing for your plant.
- Synthetic fertilizers are also not made from renewable resources. A lot of energy must be spent on producing nitrogen and other compounds in synthetic fertilizers, and these processes take their toll on the environment.
Determining whether or not to go organic or synthetic will vary by situation and what the growers ultimate goals are. Are you trying to grow high volume in the desert of Nevada? Maybe a synthetic nutrient-fueled indoor grow is the only plausible model for a viable business model.
Likewise, are you a boutique cultivar serving a market in which consumers are willing to pay a premium for verifiably organic product? Current data seems to indicate there is indeed a rapidly growing preference for organic product, with many consumers and patients stating they value the safety as a motivating factor when purchasing organic over synthetically grown cannabis.
Personally, we’re a huge fan of organic grows because we’re wary of unintended downstream impacts of synthetic nutrients, especially given different states have different levels of stringency when it comes to waste and waste water disposal and processing. We’ve written before about the disturbing amount of plastic waste generated by packaging and we think being more eco-conscious is equally valuable, both for the earth, and ultimately for consumers and patients as well.
Herb CEO Summary
We levered experts with over a decade of growing experience to bring this breakdown of the biggest nutrient types all growers need to dial in to be successful with their cannabis crop. This doesn’t mean this is the end-all-be-all and every plant type, environment, and ultimate goal will mean each grower will need to adjust their nutrient ratios based on their particular circumstance.
In trying to build a community we welcome any additional insight other experienced growers have in terms of nutrient types, ratios, timing, and delivery systems. Feel free to sound off in the comments below!