Feeding your plants isn’t too hard, but there’s a lot that goes into doing it well. Think about a human diet; we need major things like carbs, proteins, and fats, but that’s not all. A balanced diet also requires things like iron, potassium, and electrolytes to stay healthy. In many ways, cannabis plants (or any plants, for that matter) are no different.
- Micronutrients vs macronutrients in cannabis cultivation
- Mobile vs immobile cannabis nutrients
- Cannabis macronutrients: What are they and how do they work?
- Cannabis micronutrients: Big things come in small packages
- Nutrient levels: How much is too much?
- The importance of pH in nutrient uptake
- Thoughts to chew on
Micronutrients vs macronutrients in cannabis cultivation
When it comes to cannabis plants, the three most important macronutrients are nitrogen (N), phosphorus (P), and potassium (K) and these three form the basis of any nutrient blend. This so-called NPK ratio varies throughout the lifetime of the plant with vegetating plants needing higher levels of nitrogen while plants that are flowering require more potassium and phosphorus.
Of course, these aren’t all that it takes for a healthy plant. Other macronutrients include calcium (Ca) and magnesium (Mg) but we’ll get to those a bit further down. Additionally, carbon (C), oxygen (O), and hydrogen (H) are all key ingredients in a healthy plant, but plants can typically draw these as needed from the air and don’t need to be added by growers.
But these aren’t the only things needed for a healthy plant. Micronutrients may be needed in smaller quantities, but they’re no less important. Chemicals like boron (B), copper (Cu), zinc (Zn), and more all play key roles in a healthy plant.
Mobile vs immobile cannabis nutrients
Before breaking down what each nutrient does, there’s one other important distinction to draw; that between mobile and immobile nutrients. Macronutrients (N, P, and K), as well as magnesium (Mg), are all “mobile” nutrients. What this means, is that the plant can shuffle them around wherever they’re needed most.
Therefore, any deficiencies in these nutrients are likely to appear in older growth first. This is because the plant is shifting its stores of these from older leaves to newer growth. If left unchecked, though, even the new growth will eventually show signs of deficiency.
On the other hand, many micronutrients such as calcium (Ca), sulphur (S), and iron (Fe) are immobile; once they get where they’re going, they aren’t moving again. Deficiencies in immobile nutrients tend to show up primarily in newer growth as the plant is unable to use existing reserves to support these younger leaves.
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Cannabis macronutrients: What are they and how do they work?
Now that we know a little bit about macronutrients, let’s break each one down and go over what exactly they do for the cannabis plant. While maintaining a proper NPK ratio is necessary, it’s important to remember that these aren’t the only vital macronutrients.
Nitrogen (N)
Nitrogen might just be the single most important element for healthy cannabis plants. As one of the primary components of chlorophyll, nitrogen enables plants to make the most of any available light and convert it into energy.
Keeping an eye on nitrogen levels is a must for ensuring healthy and robust growth during the vegetative phase. Any imbalance or deficiency in nitrogen can quickly cause yellowing leaves, stunted growth, and reduced yields. Luckily, nitrogen is incredibly mobile within plants, making any deficiency quick and easy to correct.
Phosphorus (P)
Another mobile nutrient, phosphorus is crucial in developing and supporting new, immature growth. Present in every living plant cell, phosphorus is at least partially responsible for energy transfer, photosynthesis, and carbohydrate metabolism. On top of this, phosphorus helps move other nutrients around within plants and is the element responsible for passing down genetic traits to future generations.
During the vegetative stage of your cannabis plant’s life cycle, phosphorus encourages healthy root growth and enhances stem strength. As plants progress into flowering, phosphorus boosts disease resistance and contributes to the growth of flowers and overall plant productivity.
Potassium (K)
The importance of potassium is impossible to understate. Even a small interruption in access to potassium poses significant risks to plant health and development. Potassium plays a key role in a wide range of essential functions within the cannabis plant, such as promoting new growth, regulating plant metabolism, stress tolerance, and enhancing root growth.
Additionally, potassium is crucial for proper water management within the plant. By regulating the opening and closing of stomata (pores for gas exchange in plants), potassium helps control water loss during photosynthesis.
Calcium (Ca)
Calcium serves several functions crucial for healthy cannabis plant growth. It contributes to cell wall structure and stability, aids in root and shoot growth, and helps prevent disorders like bud rot. Additionally, calcium regulates enzyme reactions, supports nutrient uptake, and helps manage plant stress responses.
The presence of calcium ensures proper cell division and membrane function, promoting overall plant health and resilience. As an immobile nutrient, calcium can’t be shuffled around the plant so fixing a calcium deficiency can take longer than some others.
Magnesium (Mg)
Magnesium is another essential nutrient for cannabis plants and is closely related to calcium. Magnesium is a key building block of chlorophyll making it necessary for photosynthesis and overall plant production.
Interestingly, magnesium and calcium compete for uptake by plant roots, with higher levels of one potentially reducing a plant’s ability to absorb the other. Maintaining a balanced ratio of magnesium to calcium is essential for optimal plant health. Luckily, several CalMag mixtures on the market are perfectly balanced for weed plants.
Sulphur (S)
Cannabis plants need less sulphur than other macronutrients, but that doesn’t make it less important. Sulphur is needed for plants to form essential enzymes, plant proteins, vitamins, and amino acids.
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Cannabis micronutrients: Big things come in small packages
While macronutrients are undeniably the most important to a healthy weed plant, micronutrients can’t be ignored. Needed in smaller quantities, true deficiencies are fairly uncommon. However, a lack of one or more micronutrients can lead to poorer plant health and reduced yields.
Each of these micronutrients, on their own, plays only a small role but how they work together means that they can’t be ignored. Any micronutrient blend on the market should contain all of these (and possibly more) meaning that you only need a single bottle to cover all of your needs.
Boron (B)
Boron is used by cannabis plants to reinforce cell walls and helps the plant maintain a rigid structure. A lack of boron may lead to symptoms such as brittle stems, death of new growth, deformed leaves, and/or reduced flowering.
Copper (Cu)
Cannabis plants use copper to metabolise carbohydrates and proteins. This means that without ample copper, plants can starve. Yellow leaves, poor bud growth, and an increased susceptibility to disease may characterise a copper deficiency. Luckily, copper is fairly mobile and correcting low levels shouldn’t take long.
Iron (Fe)
Iron assists in the maintenance of chloroplasts. These are the actual structures that contain chlorophyll and allow the cannabis plant to photosynthesise. Without adequate iron, plants will be less able to create the food and energy they need, resulting in weaker growth and reduced yields.
Manganese (Mn)
Manganese is crucial for several of a weed plant’s more important functions like nitrogen assimilation, respiration, and photosynthesis. Furthermore, it assists with pollen germination and pollen tube growth, making it vital for plant reproduction.
Molybdenum (Mo)
Molybdenum is a highly mobile nutrient that helps certain plant enzymes get the most out of other nutrients. By helping convert things like nitrogen into forms the cannabis plant can use, molybdenum is one of the unsung heroes of growing.
Nutrient levels: How much is too much?
With all of these nutrients being needed in such specific quantities, it can be overwhelming to try and balance them all. Luckily, there are several available formulas out there that take the guesswork out of feeding your cannabis plants. However, knowing which to use is a skill set in itself.
NPK ratios
Almost any fertiliser you buy will have three numbers on the front of the bottle. This is the NPK ratio and it’s the most important aspect of any nutrient mixture. As mentioned above, these three elements (nitrogen, phosphorus, and potassium) are the three most important nutrients in plant development.
- Nitrogen promotes healthy leaf growth
- Phosphorus is required for robust root development
- Potassium assists with the growth of flowers
These NPK numbers are commonly written in two ways; as a ratio or as percentages. For example, an NPK ratio of 1:3:3 means that for every one part of nitrogen, there are three parts of phosphorus and potassium. That’s good, but it doesn’t tell the whole story. Many products list their NPK numbers as percentages, like 5-10-10. In this case, it means that the solution contains 5% nitrogen and 10% phosphorus and 10% potassium. Most products list these numbers as percentages.
Different plants require different mixtures, so you can’t just use any old garden fertiliser for weed. For example, tomatoes need an NPK of 4-8-10, while cannabis requires an NPK ratio of 16-4-8 during vegetation. This highlights how important nitrogen is for vegetative growth, followed by potassium for root development. Since the plant isn’t yet producing any flowers, phosphorus can be kept to a minimum.
But this same mixture won’t work forever. When a cannabis plant gets into the flowering stage, you’ll need to switch formulas. During flowering, a ratio of 4-10-10 is ideal as the plant needs less nitrogen and much more potassium.
Micronutrient levels
The amount of micronutrients that plants require is incredibly small (as the name suggests). So small, in fact, that trying to measure each one on its own is nearly pointless. These aren’t measured in ratios, or even percentages, but in parts per million (PPM).
| Micronutrient | PPM during vegetative stage | PPM during flowering stage |
| Boron (B) | 0.5 | 5 |
| Copper (Cu) | 0.1 | 0.5 |
| Iron (Fe) | 2 | 10 |
| Manganese (Mn) | 0.5 | 5 |
| Molybdenum (Mo) | 0.01 | 0.05 |
As you can see, these nutrients are needed in much greater concentrations during flowering but even then, the numbers are tiny. The most abundant, iron, only needs 10 PPM, which is only 0.001% of a nutrient mixture.
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The importance of pH in nutrient uptake
Nutrient levels aren’t the whole story, though. The pH of a medium is incredibly important for a plant’s ability to properly absorb nutrients. For growing cannabis in soil, the pH needs to be between 6.0 and 7.0 while hydroponics should be in the 5.5-6.5 range. Why? Anything outside of this will block your plant’s ability to get vital nutrients from the growing medium.
This is known as nutrient lockout and it happens because pH can alter the chemical forms of nutrients. For example, overly alkaline soil (with a high pH0 can block out nutrients like iron, manganese, zinc, copper, and boron. On the other hand, acidic soil (low pH) can hinder the absorption of phosphorus, calcium, magnesium, and molybdenum.
Checking the pH and EC of your water before every feeding is essential for ensuring a well-balanced environment for your plants.
Thoughts to chew on
While NPK ratios might get all the attention, the importance of maintaining a well-balanced cannabis nutrient regimen can’t be overstated. Only by properly balancing macro and micronutrients can you give your plants the tools they need to reach their fullest potential. That’s certainly enough to digest! Any questions? Don’t hesitate to ask!
