Nutrients are a crucial component of the marijuana life cycle and must be available as soon as leaves start to appear. Without the right nutrition, buds may not reach their full potential and yields may be lower than they could have been. While the vegetative and flowering stages require regular feeding, overdoing nutritional supplementation can lead to problems too—balance is essential.
Nutrients can be grouped into different categories: micro or macronutrients and mobile or immobile. Macronutrients are the building blocks plants need in the most abundance. Micronutrients are essential to biological functions but in lower concentrations. Mobile nutrients flow throughout the plant. Immobile nutrients, as their name implies, are fixed in one spot and cannot be moved to other places where the plant may need them.
Nutrient uptake often is reliant on pH level. If the growing medium falls out of the optimum pH, nutrient lockout may occur—meaning the plant may fail to absorb what it needs to thrive. The ideal pH range for cannabis is 5.8 to 6.3, but it can fluctuate slightly based on the growing medium and feeding schedule.
Aside from water and carbon dioxide, all plants need nitrogen (N), phosphorus (P), and potassium (K). Referred to for convenience as NPK, in cannabis this trio of mobile elements is vital for growing buds that are deliciously smooth to smoke. NPK promotes photosynthesis, cell development, and overall plant development.
NPK ratios vary depending on the growth stage. During vegetative growth, nitrogen is emphasized with an NPK ratio of three-one-two, meaning three parts nitrogen, one part phosphorus, and two parts potassium. Once buds start to form, the ideal ratio shifts to emphasize phosphorous with one-three-two. In the final weeks of the vegetative stage (also known as ripening), many growers opt for a zero-three-three ratio.
A nutrient deficiency during the vegetative stage can be relatively easy to spot. One telltale sign is yellowing leaves. If you see this, make sure to test the pH of your water immediately and adjust accordingly so your plant can absorb nutrients appropriately.
When it comes to nutrients, the growing medium will play a big role in how you feed the plants. When using soil, the plants will absorb essential nutrients from the ground automatically. Instead of applying nutrients, some growers add things like bat guano to the soil, which will adjust the microbiome naturally. The plant’s root system will be able to uptake whatever it needs, making precision dosing less critical.
For hydroponic growing media like coco coir or rockwool, nutrients are fed directly to the plant through the water. In this case, maintaining accuracy and balance in the feeding schedule is critical.
Macronutrients are the nutrients the plant will use in the most abundance during its life cycle. These nutrients are oxygen, hydrogen, carbon, nitrogen, phosphorus, and potassium. All of these nutrients are required throughout the life cycle, but the plant will use more nitrogen during the vegetative stage of growth.
“Nutrient requirements vary throughout the cannabis life cycle,” said Wisconsin-based commercial cultivator, Kurt Kinneman. “As the plants begin to flower and finish, the nitrogen use will decrease, and the phosphorus and potassium use will go up as plants begin to focus on flower and production instead of leaf and stem production.”
N, P, and K are all mobile nutrients. This means deficiencies first will appear in older leaves and stems as the plants use those nutrients to keep pushing new growth. If the deficiency is not corrected, new growth will start showing signs of a deficiency.
In addition to the main macronutrients, plants also require three secondary macronutrients: calcium, magnesium, and sulfur. Calcium improves the absorption of other nutrients by the roots and helps move them throughout the plant. It’s also an essential building block for enzyme functions.
Calcium also helps soil-dwelling organisms break down organic matter into usable nutrients for plants and helps nitrogen-fixing bacteria grow nodules on plant roots to fix atmospheric nitrogen to the soil.
Micronutrients may only appear in trace amounts in plant matter, but they play a big role in overall function. When any micronutrients are lacking, overall plant health and yield can suffer. However, it’s similarly important to avoid an overabundance of micronutrients, which can cause toxicity that also can be detrimental to overall crop yields.
Boron (B), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), molybdenum (Mo), and chlorine (Cl) are some of the most abundant micronutrients. They are all crucial to crops but may only be present in small amounts.
Organic vs. synthetic nutrients
In organic growing, you feed the soil directly. The microbes, amino acids, and fungi in the soil turn the inputs into usable nutrients plants can uptake. Synthetic nutrients come in a form that is readily available for plants to uptake.
When using synthetic nutrients for weed plants, you can use a smaller pot and water more frequently to dial in your dry back for crop-steering. Organic cannabis nutrients require a much larger pot size and prefer constant moisture with very little dry back.
Best nutrients for vegetative stage
During the vegetative stage of growth, it is important to look for a nutrient solutions blend that has a high nitrogen concentration. When growing with synthetic nutrients, there typically will be a special vegetative blend.
“Heavy 16 is a brand that has a special feeding chart they provide with their five-part nutrient line,” Kinneman recommended.
When growing organically, you want to use inputs like feather meal that have a high nitrogen content. You also will want to use fermented plant extracts made from vegetative growth. Kinneman suggests hemp, comfrey, and nettle alongside the best cannabis nutrients.
Many organic growers use compost tea to help promote a healthy microbiome. When brewing compost teas during vegetative growth, it’s important to create a tea with high microbial content instead of high fungal content. It’s the opposite for the flowering stage of cannabis cultivation.
Best nutrients for flowering stage
The macronutrients phosphorus and potassium are essential to promote flower growth and bud production. In addition to helping grow large flowers, these macronutrients are required for root growth and promoting overall nutrient uptake.
Calcium and silica help build and strengthen cell walls to support big flowers and protect against infection and disease. These critical micronutrients also enable other nutrients to be absorbed more readily.
The building blocks of bud
- Cannabis may grow like a weed, but using the right inputs can help produce top-shelf bud.
- Nutrients are one of the key pieces of the puzzle, promoting healthy growth and resinous nugs.
- Balance is key when it comes to these elements—ratios may need to be dialed in depending on the stage of life and growing medium.
- Cultivators should visually inspect their plants daily and test the pH regularly to ensure optimal nutrient levels and perfect harvests.
Can you grow cannabis without nutrients?
No, nutrients are food for the plants. Things like air and water are essential nutrients, and a plant will be limited by the least amount of a nutrient that is available. Just like a human, plants need all the required nutrients to grow.
How often do you give cannabis plants nutrients?
When growing hydroponically or with a soilless medium, you feed with almost every watering or reservoir change. In organics, the nutrients are in the soil already. You can feed the microbes in the soil once a week using compost teas, which are fermented plant extracts.
How often should I feed my cannabis plants nutrients?
Hydroponic growing requires an almost constant feed. Whether you are using plain water or a nutrient blend, your solution should have a pH of 5.8 to 6.3 to allow the plants to take up the most nutrients. If you are growing organically, the pH can be from 6.0 to 7.0 but can even go outside this range.
What are the most important nutrients for cannabis growing?
The most-used nutrients for cannabis plants are nitrogen, phosphorus, and potassium. However, it is tough to pick one essential nutrient, because a plant’s growth will be limited by the least available nutrient. Water is the nutrient plants use the most, but having the proper balance of micro and macronutrients is the most important part.
Should you use nutrients every time you water?
Depending on your growing medium, you may use nutrients every time you water. However, you want to be mindful of how much you use in order to avoid causing nutrient burn, which can damage plants. Check the pH of your water regularly to ensure balance.
Which nutrients do plants need during the flowering stage?
Macronutrients phosphorus and potassium and the micronutrients calcium, silica, and magnesium are critical for the flowering stage. These nutrients help promote rapid growth and robust bud development.
When should I stop using nutrients?
One to two weeks before your plants finish, you should cut back on all the nutrients and cut out nitrogen completely. Let the senescence process occur naturally, and allow the plant to use all the nutrients in its leaves and roots to finish its life cycle.