Before October 17, 2018, people would sometimes approach the subject in a roundabout way; “Which of your products do you recommend for growing medicinal herbs in indoor containers?” (Wink wink, nudge nudge.)

Now that Canadian adults can legally grow up to four cannabis plants per household, the questions are more direct. And while general opinions on the topic naturally differ, I appreciate your desire to grow your plants organically in a safe and healthy way, be it for recreational or for medicinal use, or indeed both. After all, who wants toxic pesticide residue on something they smoke, ingest, or put on their skin? The reasons for growing organic weed are not so different from choosing organic food, really.

In many ways, cannabis is a crop like all others — in some ways, it is special. Full disclosure: My advice is based on online research and chats with growers, not on first-hand experience. A few valuable points were learned from a series of infographics and texts published in The Visual Capitalist, itself adapted from information by The Green Organic Dutchman. This I combined with what I know about how to use the products I carry.

I consider EM (probiotics), mycorrhizal fungi, kelp, and fish products essential for growing organic marijuana, with sea minerals a close runner-up.

Plants can be grown in aeroponic or hydroponic systems, or in solid growing media such as soil/compost, peat moss, and coco coir mixes, or rock wool. The following applies mainly to soil-based mixes but can be adapted for soil-less cultivation.

Phase 1: Seed or Cuttings

If you start your plants from seed, give them a leg up by soaking the seed in a weak solution of liquid kelp and EM (1 teaspoon each per 1 liter of water) overnight. Do not soak any longer, and be sure to use up the water the next day (it will not keep). No need to fertilize yet.

For cuttings, dip into the kelp/EM solution when planting and use the rest of the water to moisten the growing medium. I’m told it takes about a week for seeds to germinate, a little longer for cuttings to root.

You can continue using diluted kelp and EM as a soil drench and/or foliar spray every two weeks right until harvest. Keep with the weak solution — more is not better. In fact, it is best to frequently apply small doses of any fertilizer, rather than a whole lot just once or twice.

Phase 2: Seedling Stage or Rooted Cutting

At this stage, plants need high light and humidity, but very few nutrients yet. It lasts 2-3 weeks and is the best time to inoculate with endo-mycorrhizal fungi. These symbiotic fungi later aid in the uptake of water, micronutrients, and the important elements phosphorus and nitrogen, and protect roots from soil-dwelling pathogens.

One application lasts for the plant’s entire life, so it makes sense to do it early, ideally when transplanting into larger containers. The product must touch the roots, either by sprinkling the dry powder onto roots directly or by using water as a carrier. One heaping tablespoon (30g) of “endos”, mixed in 10 liters of tepid water, is enough to treat 40 two-gallon plants!

There is no harm in over-applying, this is just to show how economical the product is. Adjust amounts according to the number of plants and container sizes. Leftover powder stores for at least a year if kept dry, cool, and dark.

Tip: I don’t think mycorrhizal fungi work in aeroponic or hydroponic systems, as they need an aerobic soil environment to thrive. They might have limited usefulness in rock wool.

Phase 3: Vegetative Stage

Plants are putting all their energy into green growth now. This means they want less intense light and lower humidity, and ample nutrient supplies, especially nitrogen. Insect frass fertilizer or liquid fish are the fertilizers of choice. You can also alternate between the two (best of both worlds).

The frass can be mixed dry into the growing medium at a rate of 3 tbsp per gallon of soil volume. Depending on how long your plants are in the vegetative stage, repeat as a topdressing at 1 to 2 tbsp/gallon of soil every two to three weeks. Frass has a pleasant smell and is easy to handle. For foliar application, mix 1-2 tsp of frass into one gallon of water, strain, and spray. Use up any leftovers promptly as the liquid won’t keep.

Fish concentrate, diluted with water, works both in the soil and as a foliar spray, though it is smellier than insect frass. Use 1 cup (250mL) in 2.5 liters of water (1:10 dilution) to drench the soil. For spraying, go down to 4 tsp (20mL) in 1 liter of water (1:50 dilution). Repeat once or twice during vegetative growth. Tip: Do not spray fish on buds/flowers…!

Phase 4: Flowering Stage

As plants decrease green growth and develop flower buds, their needs change from nitrogen to phosphorus plus a variety of trace elements. Remember, if you used mycorrhizal fungi, you can reduce inputs of phosphorus fertilizers because these fungi help plants pick it up more efficiently. Also, keep using your kelp/EM solution throughout.

Discontinue the use of frass or fish, and turn towards broad-spectrum fertilizers like liquid kelp or, if you want to put the icing on the cake, sea minerals. This product contains 80+ different elements in minute amounts and it is particularly useful for maximizing flower and seed quality. It takes as little as two applications of sea mineral concentrate, about two weeks apart, diluted 1:50 with water for soil application (4 tsp/20mL in 1L of water) and 1:100 to spray on foliage (2 tsp/10mL in 1L of water).

Sea minerals last almost indefinitely so what you don’t use this time around, you can keep for the next crop. Store undiluted, cool, and dark.

Phase 5: Harvest – Process – Enjoy!

After harvest, unless there were major problems, the spent growing medium can often be mixed with some high-quality compost and fresh soil amendments and re-used for the next crop. You will have to apply mycorrhizal fungi to the new plants as the mycelium does not persist in the soil after the old plants are removed.

Beyond the products listed above, people have successfully used humic acids (for complex carbon molecules that support nutrient storage and exchange) and compost tea (for microbiology and disease prevention).

I would also recommend glacial rock dust (for trace elements) if locally available, and possibly soft rock phosphate (for phosphorus and calcium) and oyster shell powder (for calcium plus trace elements). Stay away from animal manure unless it has been properly composted (minimum one year, better two). Well made, aerobic, plant-based compost and worm castings, on the other hand, are hugely beneficial, not only for their (rather minor) nutrient content but especially for a wealth of beneficial microorganisms.

Happy growing… and as always, I invite your feedback and questions!