How To Grow Cannabis in Coco Coir

Coco coir has made a name for itself as a growing medium in the cultivation scene. Now widely used by growers, people have realised the benefits of using coco coir for its ability to provide roots with the perfect home they need, to give cannabis plants the life they deserve!

You may have heard of coco coir but still have no idea how it can be used for cultivating cannabis. Coco coir is a highly effective substrate that is actually very straightforward to use. We've created this guide to give you some top tips on how to get started with coco coir.

Coco Coir: What Is It?

Coco coir is made by grinding up coconut seed husks. This results in an inert growing medium that is light and has a texture similar to that of soil, but acts in different ways. Coir is extremely versatile and is especially good for cultivating cannabis.

Coir, also know as coco peat or simply coco, is almost completely free of nutrients. Apart from the phosphorous and potassium naturally present, it provides nearly no nutrition to cannabis plants.

Why Grow Cannabis Using Coco Coir?

Before we get started, let's take a look at why using coco coir is so good for growing cannabis. Coco coir acts like a hydroponic substrate but is often used with or instead of soil to improve aeration and water retention.

There are many advantages to using coco coir if used in the correct way. Whether you are growing in the ground, with pots or hydroponics, coco fibres can improve your garden significantly.

• Adequate Drainage - Because of its fibrous nature, coco coir drains water particularly well, reducing the risk of overwatering.
• Water Retention - Even with effective drainage it still manages to hold enough water content to keep roots hydrated.
• pH Neutral - Has an optimum pH level of 5.6 - 6.2, the ideal range for cannabis cultivation.
• Effective Aeration - Coco coir has a light, airy structure which allows for plenty of oxygen circulation around the root zone.
• Eco-friendly - Coconut husks are a natural, renewable resource that can be recycled 2 - 3 times for growing.
• Affordable - Cheap compared to high quality soils or other mediums such as peat moss.
• Less Pests Than Soil - Using coco as a substrate provides roots with an inert environment which does not attract many pests or harmful bacteria.

Grapey Walter, Mephisto Genetics

Types of Coco Coir

The structure of coco coir depends on how it is processed. Coco fibre is often compressed and bought in blocks which are rehydrated when they are ready to use. Coco coir can also be purchased uncompressed in bags.

Fibre - Coco fibre is stringy and comes from earlier stages of coconut husk processing. Usually compressed into a block. Provides improved space for aeration but does not absorb much water.

Chips - Chips are chunky pieces of coco husk that have the benefits of both fibre and pith coir. Coco chips allow for healthy levels of oxygen movement around roots, as well as retaining enough water.

Pith - Pith coir is probably the most similar to soil in terms of its texture. It can be compared to peat moss but is brown in colour. Pith coir holds more water than other types of coco, reducing oxygen flow.

Tip: Coir works very well as mulch for indoor or outdoor gardens to help protect your top soil.

Growing Cannabis In Coco Coir

Preparing Your Substrate

There are many ways coco fibres can be used with other mediums or amendments to create the perfect substrate for your cannabis. The first step with coco usually involves rehydrating and rinsing.

Buying coco in a compressed form will require you to break it apart in a pot/bucket with warm water and let it sit for a while to soak. Start with small amounts of water and add more until it becomes fluffy and fibrous. When it's ready it should be moist and light, not completely drenched and heavy.

Buffering the coco coir with a calcium/magnesium solution after it has been rinsed is advised. This is because calcium and magnesium are absorbed quickly by the coco fibres before plants get a chance to use it, leading to deficiencies early on. 

Coco coir can be mixed with soil to improve aeration and drainage. If you want to use it as an alternative to potting soil, we recommended that you mix it with perlite. Always check the quality of your coir before purchasing to make sure it does not contain any chemicals or other harmful by-products like high salt concentration.

A well mixed coco substrate should contain at least 10 - 15% perlite. Although on the expensive side, there are pre-mixed bags of coco coir available to buy which already contain perlite, saving you some steps. 

Cannabis plants in pots benefit from a 2 - 3 inch layer of clay pebbles at the bottom of containers to aid oxygenation and drainage. Pots can then be filled with your preferred coco coir blend.

Nutrients For Coco Coir

The fibrous structure of coco coir is a perfect home for the development of beneficial microorganisms. Since there is almost no nutritional value in coco, we must provide the required minerals ourselves. There are nutrients designed specifically for coco coir, however most liquid nutrients for hydroponics can be added without issues.

Organic fertilizers can also be used in coco coir, but overall growth may be slower. Either way, proper feeding should start in the seedling cycle once cannabis plants have 2 - 4 sets of leaves.

Check the guidelines on the nutrient bottles, but start with half strength and work your way up with each feeding if plants need it.

This is where you need to decide how much your plants are consuming and adjust accordingly. If they are growing slowly or showing signs of deficiency, you might need to up your regime if you have been giving low doses. Just make sure you do not over feed your cannabis plants. Watering more regularly with lower levels of nutrients is recommended. If possible, try to get into the habit of giving enough water to last plants a day or two. 

Most store bought cannabis fertilizers will contain the necessary NPK levels, as well as some added micronutrients. Normally, brands offer different bottles for each stage of growth. In this sense, it's good to stick with one brand for consistency and compatibility of nutrients.

Nutrients for growing in coco coir:

• Root stimulators - Supplements to aid development of rhizobacteria around roots can be used until the flowering cycle.
• Nitrogen - Very important for the early stages of foliage and plant growth. Less important for bud production during flowering.
• Potassium and Phosphorous - Already present in coco coir, but should be readily available throughout the grow cycle. Plants benefit from higher concentrations in bloom.
• Micronutrients - Although not always essential, trace minerals such as copper, manganese, zinc, boron, and molybdenum are usually mixed into cannabis liquid solutions.
• Calcium - Deficiency is common when growing with coco coir. Cal - Mag (calcium/magnesium) can be added during vegging, reducing the dosage with watering until the early stages of flowering.

You can get an idea of how some of these important minerals are absorbed at varying pH levels:

Note: Liquid fertilizers are often highly concentrated and the recommended schedule can be too strong for a cannabis plant.

Coco Coir Problems

Coco coir is an extremely reliable growing medium but it would only be fair to discuss some of the problems associated with using it. As always, it will help you to do your own research so you can grow the best plants possible.

Low Quality Products - Coir is often processed to a low standard, using chemicals and salts which can be harmful to cannabis plants. Make sure you choose high quality, clean products.

Fluctuations in pH levels - Always use a pH testing kit on your nutrient solution before adding it to the substrate. Monitor the pH around the roots by checking the pH levels of the runoff water every week or two.

Nutrient Management - Salts can build up easily in coco coir, which can burn roots and create toxicities or deficiencies. It is a good idea to give plants fresh, pH'd water in between feedings.

Conclusion

Coco coir is definitely worth trying if you are interested in growing cannabis. Even if you come from a complete soil growing background, try adding some of this into your next mixture so you can see for yourself how effective and easy it is to use.

When it comes to growing cannabis, there is always something new to discover, so feel free to share your coco coir growing experience with others in the comments section below!

External References

Coir - Coconut Cultivation, Extraction and Processing of Coir. - Jayasekara, Chitrangani & Amarasinghe, Nalinie. (2010)

Coir-based growing substrates for indoor cannabis production. Acta Horticulturae. - Caplan, Deron & Dixon, Mike & Zheng, Youbin. (2019).

This article was updated September 2020