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Nutrients for Fertilizing Cannabis Plants

June 3, 2016

Cannabis plants require nutrients and micronutrients such as nitrogen, potassium, phosphorous, calcium, iron and many others. These are delivered to the roots through the water in the soil. But usually the soil doesn’t provide enough nutrients, so growers must add fertilizer or other additives. Nutrients and micronutrients in these fertilizers will help grow healthier plants.

Fertilizing the soil is not so much a consideration of if but when. Some growers add fertilizer to their soil all the way until harvest, while others do so mere weeks or even days prior to harvest.


Fertilizing with Perlite and Vermiculite

Perlite and vermiculite are commercial fertilizers produced when mica is heated to extremely high temperatures. This causes its minerals to enlarge and become porous.

Perlite and vermiculite naturally create:

  • Magnesium
  • Calcium
  • Potassium


These nutrients and micronutrients will blend into your soil, offering rich and natural soil additives. In pellet form, perlite and vermiculate eventually mix in with the soil and distribute minerals throughout the plant.


Here are some important tips about using these and other fertilizers:

CHECK: Rotting vegetables and animal manure should never be placed directly on indoor soil. Instead, break them down to activate premium absorption by the roots.

CHALK: If you’re using compost indoors, consider adding chalk for lightening up the soil. For outdoor growing, insects, water and worms will naturally help break down manure, compost and the like, thus promoting better water absorption via the roots.

JUST DON’T: Avoid any fertilizers that claim to be “extended” or “slow releasing.” These are intended for regular plants and can cause issues with your plants that any grower can do without.

BURNED OUT: If your leaves start turning yellow around the base of the plant, add more fertilizer. Be aware that your plants can suffer from fertilizer burn if they are “overdosed.” If your leaves drop, this is what has happened.


Some Product Recommendations

Red’s Premium Mix is a relatively new product in Oregon and Washington, although Colorado is no stranger to this formidable mix. Produced at family-owned Miller Soils, Red’s Premium Mix has commanded its fair share of attention lately from expert growers.

Biochar is an essential ingredient in Red’s as it helps hold water in the soil, buffers pH levels, modifies nutrient release and lessens bulk density. Biochar is a natural byproduct derived from forest fires and designed with sustainability in mind, along with leaving less of a carbon footprint.

Red’s Premium Mix also contains:

  • Coconut coir
  • Peat moss
  • Perlite
  • Pumice


Another worthy growing mix is Miller Soils’ Biochar and Biology mix, or Bio-Mix. It is used for:

  • In-house mass plant production for custom blends
  • Providing a light and airy growing mix

Read more about Miller Soils here.

Dyna-Gro Bloom and Dyna-Gro Foliage-Pro also are excellent solutions for fertilizing your plants. Foliage-Gro is applied to the soil during the vegetative stage, while Bloom is applied during the flowering stage. Use them consistent with package directions during the entire growth cycle of the plant.


Soil Nutrients, Additives and Tips That Might Surprise You

We always like to see what’s new or unusual in growing cannabis. We figured you do, too, so here are some quirky-but-trusted tips you should consider:

  • Urine – No one is suggesting that you urinate on your plants. In fact, please don’t, because it will kill them! But given the right amount, human urine provides plenty of nitrogen. Use a commercial mix along with the amount of urine that is yielded by an average visit to the bathroom. Be sure to apply it to your plants immediately because the longer you wait, the faster harmful ammonia will form.
  • Chicken manure – Compost that contains chicken manure is a great option for fertilizer. It can increase yields and produce some quality plants, especially in its organic, slow-release form.
  • Wood ashes or lime – If you are an outdoor grower with soil that is naturally acidic, consider adding wood ashes to the soil, since they cancel out acidity. An alternative is lime, which can be purchased from your local garden center.
  • Vinegar and baking soda – Outdoor plants naturally take in carbon dioxide (CO2) and exhale oxygen, and white vinegar is a fantastic source of CO2. Take a 1-liter bowl with some baking soda in it and mix in one drop of vinegar every two minutes. You’ll feel like you’re back in science class when the two elements combine to make CO2, and your outdoor plants will thank you for it.


Additional resources:




By Kaye Eisele

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