This website receives a commission for using affiliate links within our content. Although we receive commission for using and linking to these products, all of our opinions and suggestions are recommendations only.

Feeding Your Marijuana Plants

Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg) and Sulphur (S) are the marijuana plants basic necessities for nutrients, each serving a different yet equally important role in the plants health and growth. To help with remembering these main nutrient requirements, growers refer to the elements as NPK and CalMag.

Growth requires more than just water. That is, plants need certain nutrients to grow healthy and produce tasty flowers or buds. We can feed our plants in many ways.

Fertiliser types

Fertilisers are made to “feed” plants micro and macro nutrients. Certain fertilisers or nutrient lines cater to different plants with different elements and nutrient schedules.

Cannabis nutrient schedules can include organic, chemical, or synthetic nutrients, or a mix. There are pros and cons with each option. It comes down to preference, location, availability, and budget when it comes to choosing fertilisers.

Artificial/Chemical Fertiliser

This is a great option because chemical or synthetic fertilisers are made with precise NPK ratios, micro and macronutrients for each stage. Synthetic/chemical fertilisers provide fast-acting nutrients that help plants grow quickly and healthily. This is critical when correcting nutrient deficiencies quickly. Chemical fertilisers are great for growers who want to maximise yields and grow time.

To avoid over fertilisation or nutrient burn, growers must follow chemical fertiliser instructions and schedules. Using too much fertiliser can harm, delay or kill your plants. App for planning and reminders!

Organic Fertiliser

Natural and organic fertilisers are made from mineral (limestone), animal (manure, guano) or plant sources (compost, seaweed extract). Organic fertilisers have been used for centuries to grow strong plants. Such as guano or bone meal, which may require composting or treatment. Guano fertilisers are made from bat and seabird excrement.

There are also ready-made compounds like earthworm castings and vermicompost. Worm castings are used to make vermicompost, a type of organic fertiliser rich in beneficial microorganisms.

Fertilisers: Organic vs Chemical

Both methods can yield great results if properly executed. Chemical fertilisers have the advantage of being instantly available to plants. When applying chemical nutrients, be cautious of nutrient excess stress or burn. Always read the label and start with a low dose and gradually increase it.

Organic alternatives are more eco-friendly than chemical alternatives. Some organic compounds need more time in the soil to become plant-available elements. Most animal manures (rabbit, horse, chicken, sheep, etc.) must be composted first.

Preparing soil for cannabis plants

Adding nutrients and perlite to soil

Cannabis micronutrients and macronutrients

These nutrients are absorbed by plants from the grow medium, air, and water. Cannabis plants require more macronutrients than micronutrients, so they require more macronutrients.

Plants get their basic elements, carbon, oxygen, and hydrogen, from the air and water. Keep your tent or grow room well aerated to ensure your plants get enough CO2 and O2. Water is also required for basic plant functions. If potable water is not available in your area, use bottled water. Some water filters, such as carbon-based filters, are great for cannabis watering because they remove chlorine. You can also let water sit for 24 hours to let the chlorine evaporate.

NPK
The main macronutrients in plant nutrition are nitrogen (N), phosphorus (P), and potassium (K). They help Cannabis plants grow strong, healthy, and produce a large final crop.

Micro and macronutrients
These are calcium, magnesium, and sulphur. Plants, like animals, need these elements to thrive.

Aside from macronutrients, micronutrients like manganese and boron are found in most fertilisers in smaller amounts than macronutrients.

Fertiliser numbers to read
It’s easy to get overwhelmed by the sheer number of “cannabis nutrients” on the market. Learning about nutrients will help you read fertiliser labels. For now, just a few things to know.

You must learn to read fertiliser labels if you intend to use Cannabis nutrients.

Most fertiliser labels have three numbers: nitrogen (N), phosphorus (P), and potassium (K) (K). This is NPK. The percentage of each nutrient in the solution. For example, NPK 4 – 15 – 13 means 4% nitrogen, 15% phosphorus, and 13% potassium.

Cannabis has specific nutrient ratios for each stage of development. The NPK 16-16-16 all-purpose fertiliser may be great for your lawn, but not so great for your Cannabis plant.

If there was one correct formula with perfect NPK ratios, every brand would do it. Instead, you must maintain a balance, but the percentages vary by product or line.

NPK Cannabis Nutrient Ratios – Jane NPK Fertiliser
Different fertilisers contain essential nutrients for Cannabis plants. Every plant stage has its own requirement of nutrients. The label usually includes a dose measure and schedule chart.

Fertilisers high in nitrogen but low in phosphorus and potassium are usually used for the vegetative phase of marijuana. E.g. NPK 9-5-8.

Fertilisers with less nitrogen and more phosphorus, potassium, and potassium are usually used for flowering. E.g. NPK 5-9-9.

Not all fertilisers are created equal! To avoid nutrient excess or deficiency, read all product labels and follow the measure guides and schedules. The plant will show us physical signs of nutrient deficiency or excess.

Some products are designed to be used from planting to harvest. Always read the label!

Cannabis fertilisers vs. supplements
Supplements are substances used to improve soil quality, plant growth, and yield. Inoculants, wetting agents, humic and fulvic acids, and composts are examples. Micronutrients may be present.

A product with a low NPK content is probably a supplement, not a fertiliser.

Such products are supplements, not main fertilisers, with NPK 1.5-0.1-3.5.

Initially, focus on having at least one base fertiliser for veg and one for flowering with the above NPK ratios (see chart). After this, you can give your plants a boost with supplements. If you only feed supplements during flowering, your plants will likely develop severe deficiencies due to insufficient P (phosphorus) and K (potassium). This can lead to poor or no budding and small harvests.

Nutrients For The Vegetative Stage

During the vegetative stage, the plant requires a lot of light and nutrients. To grow healthy plants, you must provide nutrients for the vegetative stage.

Nitrogen is essential to marijuana plants, especially during this growth phase, as it regulates protein production. It also grows the leaves and stems, affecting the plant’s size and overall strength.

Fertilisers for the vegetative stage are high in N and low in P and K. (potassium). NPK 9-5-8.

It is most common in the veg stage. Nitrogen deficiency causes yellowing old leaves at the plant’s base and light green foliage. This can be caused by nutrient toxicity or overfertilisation.

Nutrients For The Flowering Stage

The flowering stage is when marijuana plants produce flowers or buds.

During this phase, phosphorus and potassium are consumed heavily. To give the plant these nutrients, apply a fertiliser solution during the flowering stage. Unlike the vegetative stage, the flowering stage requires less nitrogen.

Fertilisers for flowering contain less nitrogen and more phosphorus and potassium (potassium). NPK 5-9-9

Proper flowering plant nutrition will result in a healthy plant and an abundant harvest, which is what every grower wants.

Biostimulants and flowering stage supplements improve fertiliser absorption, resulting in thicker, more compact flowers with better flavour. They boost terpene and cannabinoid production, as well as plant resistance to disease and stress.