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The Soil Nutrients Needed to Grow Organic Cannabis

By Michelle Pugle

Soil is the life force supporting every non-hydroponic organic garden. Comprised of organic matter like humus, animal manure, and compost, as well as beneficial microbes and fungi, fertile organic soil is alive and teaming with the necessary macro and micro nutrients for your organic cannabis plants to thrive. 

It’s important to understand the beneficial role each nutrient plays in the growth process of your plants. You see, over time, even organic soil can degrade and require additional inputs of these essential nutrients. If you’re working with outdoor soil systems, you may even need to add a combination of these soil nutrients before planting begins. Otherwise, you’re setting yourself up for potential failure and frustration.

Knowing the purpose behind specific nutrients also helps you detect deficiencies in early stages and act accordingly, thereby saving your crop and ensuring a hearty harvest. 

So what soil nutrients are necessary for growing organic cannabis?

Macronutrients — The MVPs

Every healthy organic soil system requires the following macronutrients: nitrogen (N), phosphorus (P), and potassium (K). While other elements are also important for the overall viability of your soil, these three are typically required in the largest quantities. 

Here’s why.


Nitrogen is a crucial part of chlorophyll, the green pigment enabling plants to use sunlight to convert carbon dioxide and water into oxygen and glucose (energy). Without it, your organic cannabis plants are essentially starving and cannot grow. 

Your plants need nitrogen in every stage of growth. Along with aiding in photosynthesis, nitrogen is also a component of amino acids, the building blocks of protein. In the same way protein helps us develop stronger muscles, it helps your plants develop stronger stature so they can support bigger, denser buds.

Additionally, nitrogen is a key building block of DNA and RNA. Without it, your organic cannabis plants cannot grow or multiply. 

However, gardeners need to know that too much nitrogen can be just as detrimental to their plants as too little. Excess nitrogen results in excess stalk and leaf growth and weakened root systems. It can also be toxic to surrounding groundwater and aquatic systems.

If you suspect you have a nitrogen deficiency or excess, test your soil before doing anything else. 

If you need to add nitrogen to your organic soil system, you can do so with animal manure, blood meal, compost, and fish meal.


Without phosphorus, you will not have big, healthy organic cannabis buds. 

Like nitrogen, phosphorus plays a role in photosynthesis, respiration, cell division, and energy and water storage and use. It is a crucial component in plant growth and maturity. 

You will know your plants aren’t accessing enough phosphorus from your soil if you see the following signs: weak stems, stunted growth, bluish-green leaves, and little-to-no flowering. 

Like all things in life, too much of a good thing is always bad. Excess phosphorus is toxic to the soil system and surrounding environments, so make sure your plants actually need it before adding it to your soil.

If you’re sure you need phosphorus, look for the following organic sources: rock phosphate (rock dust), fish or bone meal, compost, and animal manure. 


Potassium is responsible for regulating water and salt levels within the plant stems so they will not wilt. It also plays a role in photosynthesis and energy transfer. 

Without adequate levels of potassium, your plants will be weak and devoid of the macronutrient necessary to support strong enough stems to house healthy buds. A lack of potassium can also lead to yellowing leaves with crispy or burnt-looking edges. 

On the other hand, excess phosphorus can interfere with your plant’s ability to uptake other nutrients, so again, be cautious before proceeding with fertilizers. A simple soil test from your garden center or online can save you from future frustration. 

You can supplement your soil, if necessary, with the following organic phosphorus sources: kelp meal, hardwood ashes, and alfalfa meal. You can also incorporate some clay soil to boost your phosphorus levels. 

Other nutrients needed

Your organic cannabis plants also need adequate amounts of macronutrients calcium and magnesium and the following micronutrients: zinc, iron, manganese, molybdenum, copper, cobalt, chlorine, silicon, and boron. The latter nutrients are needed in much lower quantities, but are still essential for healthy plant growth.

Think of the nutrients needed as puzzle pieces. While some are larger than others, all are equally important to the final picture.