Here’s a quick guide to cannabis nutrients — measuring and monitoring pH-balanced water, making compost teas, and how to guide your plants toward an optimal yield come harvest time.
Essential Cannabis Nutrients
Without the right variety of nutrients, your yield will be less abundant and your cannabis buds won’t reach full size. Cannabis nutrients are divided into three parts: primary nutrients, secondary nutrients, and trace elements.
The three primary nutrients all cannabis plants need to thrive are nitrogen, phosphorous, and potassium — often referred to as N-P-K on soil and nutrient packaging.
Secondary nutrients include magnesium, calcium, and sulfur.
Cannabis plants also require micronutrients, or trace elements, often found in naturally occurring soils. Examples of micronutrients include zinc, manganese, iron, boron, chloride, cobalt, molybdenum, and silicon.
Sometimes, growers incorporate enzymes or specific supplements such as molasses so plants can grow larger buds with more trichomes.
All-in-one nutrient mixtures aren’t recommended typically. Don’t overload with any single nutrient because a large dose can be toxic to the plant.
The Importance of pH
In addition to the array of nutrients, providing properly balanced pH water is necessary for a plentiful yield.
The term pH is an abbreviation for “potential hydrogen.” It measures the alkalinity and acidity of soil or soilless growing media, and dictates which nutrients cannabis plants can effectively absorb.
It is essential to check the pH of the soil or other grow medium with a properly calibrated pH meter. Regardless of growth conditions, improper pH levels can prevent a plant from absorbing nutrients, and even lead to a total nutrient lockout. Water from lakes, ponds, rivers, in-home water systems, and municipal water all contain varying pH levels. Regardless of the water’s source, the pH level should always be monitored and adjusted. Cannabis plants generally prefer an environment that leans slightly acidic, while the exact range is largely dependent on the stage of growth. The recommended parameters for cannabis grown in soil is a pH level between 6.0-6.8. For hydroponic and aeroponic environments, pH levels should be at 5.5-6.5. When your nutrient solution is not falling within the recommended range, you can adjust the pH with simple acids and bases available at nurseries and grow shops.
When measuring pH levels, it’s important to keep in mind that the recommended pH for cannabis is a range rather than a set number, as plants respond to different pH levels throughout the growth stages to adequately absorb all available nutrients.
How to Moderate and Maintain Nutrient Level Balance
The cannabis plant’s nutrient needs change as it progresses from vegetative to flowering stage. During vegetation, plants use a lot of nitrogen to help grow their lush green foliage and low amounts of phosphorus and potassium. At the flowering stage, the plant requires higher amounts of phosphorus and potassium, but very little nitrogen, which accounts for the leaves changing in color from green to yellow. Keeping this in mind when transferring plants from vegetative to flowering stages is a simple, effective way to help maintain a healthy balance of nutrients.
Nutrients enter the plant through its roots as ions with either a positive or negative charge. These ionic charges will decide how a nutrient moves through the plant. Cannabis requires both mobile and immobile nutrients. Mobile nutrients include nitrogen, phosphorus, potassium, magnesium, chlorine, nickel, and molybdenum. Immobile nutrients include calcium, sulfur, boron, copper, iron, manganese, and zinc. When a cannabis plant is deficient in a mobile nutrient, signs will sometimes show up on its lower, more mature leaves. Immobile nutrient deficiencies tend to manifest themselves in newer areas of growth near the top of the plant and at the tips. Signs of a nitrogen deficiency, for example, include rapid discoloration from green to yellow in the lower leaves. Conversely, a plant deficient in sulfur will exhibit subtle yellowing in new growth areas.
Though a visual diagnosis isn’t the most reliable indicator of a nutrient deficiency, the symptoms can help a grower identify problems more quickly.
Documenting the soil’s pH levels helps the grower observe pertinent changes over time, as well as get a better idea of the optimal pH range a crop needs for maximum bioavailability. Taking detailed notes in a grow journal throughout cultivation can help you understand which nutrients your plants need at different growth stages.
Tools for Measuring Cannabis Nutrient Levels
The only way to be sure your plants have the right nutrient balance is to measure the nutrients each time you feed your plants, ideally with tools designed for the task and the growing conditions.
Electrical conductivity (EC) meters measure a liquid’s ability to conduct electricity, which increases as the amount of soluble nutrients increases. An EC meter allows cultivators to monitor the levels of liquid nutrient solutions by monitoring its overall conductivity. It is often used in hydroponic and aeroponic systems.
A total dissolved solids (TDS) meter helps growers measure the quantity of metals, salts, and minerals present in the water, usually in units of parts per million (PPM). TDS meters are particularly helpful for determining when to add more nutrients to hydroponic and aeroponic grows.
A PPM measurement tool is used with hydroponically grown and soil-grown cannabis to measure water-soluble nutrient levels. By checking the PPM of water before it’s given to cannabis plants, growers can determine the proper amount of nutrients to add.
To prevent cannabis plants from experiencing burns or nutrient deficiencies, check the water’s pH level and its PPM frequently, especially after adding different nutrients into the water.
Plants Thrive With Compost Tea
Growers also rely on a simple mix of water and compost, called compost tea, because it contains abundant nutrients and useful microorganisms that originate in humus or regular or worm compost. They can help alleviate fungicide treatments, enhance the plants’ terpene profiles, and deter pests.
Follow these steps below to make compost tea:
- Fill up one-third of a bucket with high-quality compost. Incomplete compost might contain detrimental pathogens.
- Add pH-balanced water into the bucket. Allow this compost and water mixture to settle for three or four days, periodically stirring the mixture.
- After three or four days, strain the mixture into a new bucket through cheesecloth or other permeable fabric. Add leftover solids into a garden or compost container.
- Dilute the leftover liquid with fresh water; the ideal water-to-tea ratio is 10:1.
- Use the compost tea right away for optimal soil absorption. For already developed cannabis plants, pour the compost tea from the bucket near the root system at the base of the plants.
Feature image: A device such a total dissolved solids meter, shown, can measure in parts per million the quantity of metals, salts, and minerals present in water. (Photo via Shutterstock)