Coco coir is inert. It holds water and air, but no plant food. Cannabis grown in coco needs a full nutrient solution from the first watering. Plain water in coco gives you nitrogen, phosphorus, and potassium shortages within a week. If the coir is unbuffered, you also need extra calcium and magnesium.
coco coir vs perlite for cannabis
What coco coir is
Coco coir is the pith from coconut husks. Growers wash it, dry it, and pack it into bricks or loose bags. Coco chips and coco and perlite blends come from the same plant. Coir holds water better than perlite and holds air better than peat. Most cannabis growers run a mix of 70 percent coco and 30 percent perlite.
Why coco coir has no nutrients
Coir is a fiber, not a soil. It has no nitrogen, no phosphorus, and no potassium in a form plants can use. It has almost no humus and no mineral fraction. What coir does have is a cation exchange capacity. That surface binds calcium, magnesium, and potassium. New, unbuffered coir takes calcium and magnesium out of the nutrient solution and holds them. The plant then shows calcium spots and magnesium chlorosis on lower leaves, even when the feed is correct.
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Processing matters. Coir from coastal areas can carry sodium and potassium salts. Rinsed or buffered coir has a lower salt load. Buffered coir is soaked in a calcium nitrate solution at the factory, so the exchange sites start full of calcium.
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What to add to coco
- Base nutrients: a two part or one part hydroponic formula with nitrogen, phosphorus, potassium, calcium, magnesium, and trace elements.
- Calcium and magnesium: a cal-mag supplement at 2 to 5 mL per gallon, or a base formula built for coco.
- pH: 5.8 to 6.2. Coco drifts toward 6.5 as it dries. Check the runoff.
- EC targets: 0.6 to 1.0 for seedlings and clones, 1.2 to 1.6 for veg, 1.6 to 2.2 for flower.
- Water: feed to 10 to 20 percent runoff to flush salt buildup.
Coco compared to soil feeding
Soil carries organic matter that releases nutrients. Coco carries none. A soil grow can go two weeks on water alone. A coco grow cannot go two days. Treat coco as hydroponics. Feed at every watering, or every other watering if the coir is amended with worm castings or compost. Check EC in the runoff after each feed. If runoff EC climbs more than 0.3 above the input EC, flush with pH 5.8 water and a light feed.
Common mistakes
- Watering with plain water. This is the top cause of yellow leaves in coco.
- Skipping cal-mag. Coco binds calcium and magnesium. Soft water makes it worse.
- Using soil pH. Coco sits at 5.8 to 6.2. Soil sits at 6.0 to 7.0. A soil pH locks out iron, manganese, and zinc in coco.
- Reusing coir with no buffer. Old coir has spent exchange sites and root debris.
- Letting the pot dry out. Dry coco pulls salts out of solution and can burn roots.
Signs of a feeding problem
Nitrogen shortage shows as pale lower leaves that move up the plant. Calcium shortage shows as brown spots on new growth. Magnesium shortage shows as yellow between veins on middle leaves. Potassium shortage shows as brown leaf edges in flower. Check pH and EC before you add more bottles.