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Soil and Cannabis: What you need to know to grow

May 31, 2016

Growing cannabis plants is similar to growing other plants, at least when it comes to nitrogen (N);   phosphorus (P); and potassium (K).  It is crucial to maintain a healthy balance of N-P-K in the soil throughout each stage of cannabis plant growth whether you’re growing indoors or outdoors.  N-P-K works as a triple-threat fungicide and weed killer. And it does a lot more, such as:

Nitrogen helps provide protein to the plant. It supports chlorophyll development, which in turn produces the vegetation in plants. Nitrogen can be purchased as a soil supplement for growing cannabis in products that include:

  • Anhydrous ammonia – The least expensive type of nitrogen.
  • Urea – The second least expensive form of nitrogen, which easily blends with most fertilizer, other than ammonium nitrate.
  • Ammonium nitrate – Most expensive form of nitrogen.  This should be applied only in the summertime.
  • UAN – Consists of 50% urea and 50% ammonium nitrate.


Phosphorus is part of the plant but it can be purchased as an additive in dry or liquid form.  Phosphorus doesn’t come in various forms like nitrogen.  Using phosphorus is vital for:

  • Healthy root growth of marijuana plants.
  • Timely and adequate plant maturity.
  • Generous marijuana seed production, including aiding in bud growth.


Potassium comes in granular or dry form.  It serves to:

  • Provide choline, which is an essential micronutrient for growing marijuana.
  • Initiate the reaction of dozens of enzymes within the cannabis plant that make it big and beautiful!


For growing indoors, you’ll want to dilute the N-P-K formula to one-fourth or one-half of its original strength.

For planting outdoors, and when the marijuana plants start shooting out leaves, they will need a 20-percent balance of N-P-K.  Potting mix already has N-P-K in it, but it only lasts for three weeks.  That’s when the grower needs to begin adding these same nutrients by direct-soil feeding or as they’re watering their pot plants.


DIY Soil and More Growing Tips
To make your own soil for planting cannabis, here are some tips that pertain to indoor cannabis growing.

  • Sterilize the soil by heating it.
  • Use a combination of DIY soil with soil that already contains nutrients.
  • Make sure soil is watered often as indoor marijuana plant roots won’t grow as deep and extend as far as outdoor plants. But be sure not to over-water.
  • Compost to add natural nutrients to the soil.
  • Maintain healthy soil with a balanced pH level, making sure soil is not too acidic or too alkaline


Coco as an Additive In Soil
Also known as coco-coir, coco fibers are derived from the coconut husk. Coco coir is naturally processed and sterilized.  On its own (for soilless growing), a batch of coco can be re-used for up to three grows.

Soil tends to thin out over time. The finer the soil, the more it retains moisture and the less aerated it becomes.  Adding coco-coir to your marijuana plant soil is a savvy move.  Soil saturation all but goes away since coco doesn’t disintegrate, resulting in more oxygen reaching your cannabis plant roots and growing a more robust pot plant.

Coco can also be used by mixing it with:

  • Compost
  • Perlite
  • Organics


Additional resources:





By Kaye Eisele

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