Coco coir is a popular root zone media choice for growing marijuana. It can be easy to use, and some growers use it for more than one crop, which saves money. But it often causes problems for your marijuana plants—harming growth rate, potency, yield and your bank account—until you master these important coco coir facts…

Marijuana Coco Coir Fact #1: Coco Coir Manufacturing Standards

As with manufacturers of gardening soil, soilless mix, and rockwool, there are multiple coco coir manufacturers—and very few make quality substrates.

Coco coir comes from coconut husks. The quality of coco coir depends a lot on where and how the husks are sourced. The quality and age of the husks are also important. Some coconut husks are loaded with sodium and toxic contaminants from ocean water or storage ponds. Other husks are too green and immature to be processed into quality horticultural material.

When coconut husks aren’t processed properly by washing them with fresh water at the right temperatures and for long enough, and by carefully treating and drying the material after washing, the resultant coco coir can cause nutrients problems that harm or kill your plants.

What’s more, coconut husks have to be expertly processed so they break down into “coco peat” fibers with the right water-holding, aeration, internal consistency, and durability for marijuana plants. The processing must be done using professional facilities, methods, and materials. If not, you see inferior coir that tends to become waterlogged or break down quickly, leading to drowning marijuana roots.

During horticultural coco coir media manufacturing, husks and fibers must be washed and treated correctly or the finished product causes severe feed program problems involving nitrogen, calcium, iron, magnesium, potassium, sodium, and chlorine.

And coco coir must also be graded, packaged, shipped and stored correctly so it works well for your marijuana garden.

You’re probably wondering what’s the best coco coir brand. I’ve tested all major brands and many off-label brands, and have experienced intermittent or pervasive problems with all of them, including Canna and Botanicare.

It doesn’t help that there are significant variations in coco coir quality batch to batch, even from the same manufacturer.

Ask your hydroponics store what brands of coco coir they most recommend. But no matter what they recommend, take a look at this next fact…

Marijuana Coco Coir Fact #2: Wash & Test Coco Coir

No matter what a hydroponics store or coco coir manufacturer tells you about the quality, pre-washing, processing, and usefulness of their coco coir product, it’s best to wash and test it yourself before you use it. What I do is buy the smallest amounts possible of the top two coco coir brands recommended by my hydroponics store. Then I test the products using the following method:

  • Put the coco coir in a two-gallon bucket that has holes in the bottom, and place that bucket inside a five-gallon bucket.
  • Using reverse osmosis water, pour 2.5 gallons of water at pH 5.7-5.9 through the coco coir, collecting the runoff water in the five-gallon bucket.
  • Test the parts per million and pH of the runoff water.
  • If the parts per million reading is higher than 450 ppm, and/or the pH is wildly out of range, repeat the experiment to see if you can get runoff water that’s less than 450 ppm and within pH range.
  • If you rinse your coco coir more than three times and it’s still showing 450 or more ppm, and/or the pH is out of range, don’t use that coco coir.
  • This rinsing and monitoring process take times and you may go through several brands of coco coir before you find a quality product. When I rinse coco coir and the runoff pH is within range and the runoff parts per million is below 300, I feel I can trust that coco coir.

Marijuana Coco Coir Fact #3:  Buying the Best Form of Coco Coir

Beyond finding properly-manufactured coco coir that performs well in runoff pH and ppm tests, you want to buy coco coir that has the right consistency and configuration. Coco coir comes in a variety of configurations, including condensed bricks, loose fiber, coco peat blocks, and coco coir fibers mixed with perlite.

The best way to grade coco coir’s usefulness in your grow op is to wash and measure it, and to physically handle and visually examine it. You’re looking for dark, clean, golden-brown fibers with the consistency of moderately-dry soil. The coco shouldn’t have clumps or fine powder.

Many marijuana coco coir growers use coco in raised grow tables for sea of green marijuana gardening while others use it in individual pots. I don’t pay the extra price for coco coir that comes with perlite, but especially if I’m growing in a grow room that tends towards high humidity, I might cut coco with 10% coarse perlite. Bricked coco is usually cheaper, but harder to work with. I suggest loose fiber.

And again–remember to first buy a small amount, so you can thoroughly inspect the coco before you buy the larger amount you’ll use for your season if you find that the coir is high quality.

Marijuana Coco Coir Growing Fact #4: Watering Coco Coir

Coco coir retains water well—too well if you’re a marijuana grower who tends to overwater. On top of that, coco coir’s appearance isn’t a reliable way of knowing when it needs more water. Coco coir should be watered when it’s 50-70% dry. But how can you determine the dryness of your coco coir?

One method works only if you’re growing in individual pots:

  • Water until about 15-20% of the water runs out the bottom of the pots and the coir appears to be thoroughly wet.
  • Weigh the pots and record their weight. If they’re evenly watered, they’ll all weigh about the same.
  • When you think 50-70% of the moisture has left the coco coir root zone, weigh the pots again.
  • The difference between the initial wet weight and the current weight is used in a percentage calculation to determine how dry the coco has become.

If you’re growing in a grow table or don’t want to weigh pots, get a tensiometer. It’s a root zone media moisture measuring device that really works. Most soil moisture meters don’t work. A tensiometer accurately measures soil water tension, which tells you the effort required by your marijuana roots to extract water from your root zone media.

Tensiometers are relatively inexpensive and can be used in coco coir, soil, soilless mix, and other root zone media. Take a look at these instructions for using tensiometers in agriculture. There is a learning curve, but you’ll be glad you’re using a tensiometer.

Two other things to know: Coco coir is particularly sensitive to salts and contaminants, because it has chemical and physical properties that interact with water and whatever’s in it in ways that no other marijuana root zone media does, so always use reverse osmosis water.

Be careful not to overwater. Too many coco coir users drown their cannabis roots, which is especially bad for tender seedlings and clones that don’t yet have fully-formed root systems.

Marijuana Coco Coir Growing Fact #5:

Some Nutrients Suck

If you use regular hydroponics nutrients or organic nutrients with coco coir, you’ll almost certainly see crop problems. I used to hate coco coir, until someone explained to me that it was the fertilizers I was using, not just the coir, that caused the problems.

So the first step in ensuring you can properly feed your cannabis plants in coco coir is to get the highest quality coco coir substrate. We’ve been testing coco coir for years, and have been greatly disappointed by all the major brands. Most of them haven’t been processed, washed, or buffered properly. Using these inferior brands, you’re forced to use nutrients made specifically for coco coir, which means they can’t be used in other substrates.

Problem is, most of the nutrients brands that claim to work well in coco don’t. Growers are forced to use cal-mag supplements that created more problems than they solve. Growers harm their marijuana plants with repeated flushing, trying different nutrients parts per million concentrations, underwatering, and overwatering.

Recently, we’ve been testing what we believe to be the world’s top coco coir. It’s made by a company called California Substrates. Look for a full-length article about their clean, properly-buffered coco soon. The good news is that using California Substrates coco, you don’t have to use special coco nutrients, and you get flawless performance that isn’t available from other coir brands.

When you use California Substrates coir and properly feed and water your cannabis plants, you get the following benefits:

  • Coco coir holds water well, so you water less, and less frequently.
  • Coco coir is an ideal host for beneficial, root-enhancing microbes.
  • Coco coir can be recycled for use in multiple crop cycles.
  • Coco coir’s favorable oxygen/water ratios provide more oxygen to roots and prevent waterlogging (as long as watering is done properly) which increases growth rate and harvest weight.
  • Coco coir is a mostly-inert medium that works well with hydroponics and organic nutrients.

There are many marijuana growers who won’t use anything other than coco coir. For them, and for anyone who hasn’t yet used coco, mastering the facts in this article guarantee you’ll be harvesting big, sticky yields from your marijuana coco coir garden.