How to grow cannabis plants in coco coir

Coco coir as substrate for plants

In this post we’ll explain how to properly use coco coir as a substrate for our cannabis plants. After years of experience with this growing medium, we believe that coco coir is the easiest choice among hydroponic substrates.

To get the most out of it, first of all we should take a closer look at its composition and properties.

Coco fibres for hydroponics

Coco coir for hydroponic cultivation

Coco coir is an organic product that comes from the fruits of coconut trees. After processing the coconuts, the remaining fibres of the husk or mesocarp are collected as waste material. These residual fibers are in the form of powder and filaments, and the mixture of both is an ideal substrate for ornamental plants or intensive hydroponic cultivation.

If we take into account the advantages of coco coir when compared to soil, we’ll soon understand why so many growers are considering growing their plants in coco. It’s important to highlight the differences between coco coir and other substrates to understand the great results obtained with this growing medium.
Firstly, it should be stressed that coco coir is an inert substrate. This means that it doesn’t contain nutrients, so we must fertilise whenever we water the plants.

The aeration capacity of coco coir is one of this substrate’s strong points. It’s an extremely soft growing medium, which enables the root system of the plants to develop much faster than in soil. A stronger root ball means more vigorous growth, which allows a reduction in the vegetative period. Also worth mentioning is that coco coir contains natural Trichoderma, beneficial fungi which enhances the development of roots and improves the plant’s immune system, creating a colony of microbial life that greatly enhances the metabolic processes of the plant.

Watering cannabis plants in coco coir

Chronic plant in 1.65 L pot with coco coir

Chronic plant in 1.65 L pot with coco coir

As we have mentioned before, coco coir contains no nutrients, so we must add fertiliser every time we water our plants. In this way, checking and adjusting the EC and pH levels of the nutrient solution is crucial to obtain good results.

The EC or electrical conductivity tells us the amount of salts – nutrients – contained in an aqueous solution. We must control the amount of nutrients contained in the nutrient solution by adding more or less fertiliser, always taking into account the needs of the plants, which mainly depend on the life stage. The pH level indicates if our nutrient solution is alkaline or acidic. pH is measured using a scale from 0.0 to 14, being “0” acidic, “7” neutral and “14” alkaline.

Plants grown in coco coir need a pH level ranging from 5.5 to 6.3, depending on the life stage of the plants. Normally, pH is adjusted to 5.5 – 5.8 during growth and 6.0 – 6.3 during bloom, which helps the plant to assimilate the most demanded nutrients at each stage.

The fertilisers used should be suitable for this substrate, with chelated forms working best. There are plenty of brands on the market which formulate specific fertilisers for cultivation in coco coir, so you can choose from a very wide range of products especially developed for hydroponic cultivation, both organic and mineral.

AK-47 marijuana from Serious Seeds

AK-47 from Serious Seeds

Mineral fertilisers are the most widely used as they are made specially for hydroponic growing systems. It should be noted that there are also fertiliser brands focused on producing nutrients from organic guano to be used with coco coir, offering new possibilities to those who miss the flavor of organic buds grown in soil.

The containers or plant pots used with coco coir must have a good drainage system as the ability to drain excess water quickly and easily is crucial for proper nutrient uptake and to avoid rot root.

Plants grown in coco coir need less amount of substrate that a plant grown in soil would require. We can use a pot of 1.65l with coco coir to get the same results than a 7L pot with soil. For larger plants, we can use 3L pots with coco instead of 11L containers with soil.

Irrigations during the first weeks should be moderate, with an initial amount of no more than 100ml per plant. This facilitates the dry/wet cycle of the substrate, thus enhancing root development. As the plants grow taller, gradually increase the amount of nutrient solution. You can also install an automatic irrigation system that will increase yields and improve efficiency.

When and how to flush the roots in coco coir

Salt excess in coco substrate

Salt excess in coco coir

Another important aspect in regard with irrigation and fertilising is root flushing, as well as nutrient excesses and deficiencies. As happens with any other vegetable, if we overfeed the plant we will compromise nutrient uptake and cause a general nutrient lockout that will probably lead our plants to death. Thus, it’s always appropriate and necessary to check both the EC of the nutrient solution and the EC of the drainage water.

Measuring the EC in this way allows us to know the level of salts in the substrate. These accumulated salts raise the nutrient concentration in the substrate, often causing an excess of fertiliser. As we mentioned, we may see deficiencies usually accompanied by general nutrient lockout, which means that the plant can’t properly assimilate nutrients.

We should always flush the substrate when the EC levels of the drainage water are higher than 2.5, using some enzyme supplement and watering the plants with triple the amount of water than the volume of the pot. Also, adjust the pH level according to the life stage of the plant and use the lowest possible EC. Flushing the substrate reduces the concentration of nutrients in the substrate and thus avoids nutrient imbalances. Most hydroponic growers flush their plants with enzymes every 15 days.

Nutrients and additives for coco coir

Canna nutrients for coco:

  • Canna Coco A + B
  • Cannaboost
  • Canna Rizhotonic
  • CannaZym
  • Canna PK13-14
  • Canna Flush

Hesi nutrients for coco:

  • Hesi growth complex for soil and coco
  • Hesi coco growth and flowering
  • Hesi root complex
  • Hesi PK 13-14
  • Power Zyme
  • Super Vit

House & Garden nutrients for coco:

  • H&G Coco A + B
  • H&G Roots Excelulator
  • Top Shooter
  • H&G Top Booster
  • H&G Bud XL
  • H&G Shooting powder
  • H&G Multienzyme
  • H&G Drip Clean

Grotek nutrients for coco:

  • Solotek Grow
  • Solotek Bloom
  • Vegetative Grow Booster
  • Vitamax plus
  • Monster Grow
  • Monster Bloom
  • Bloom Fuel
  • Blossom Blaster
  • Heavy Bloom
  • Pro Silicate
  • Final Flush

Green Hope additives for coco:

  • Root Max Root Stimulator
  • Booster Max Growth Stimulator
  • Flora Max Bloom Stimulator
  • Bio Protector
August 22, 2017 | Indoor marijuana growing

3 comments on “How to grow cannabis plants in coco coir

  1. Crip

    Hi i think i watered my seedlings too much in coco and the coco is waterlogged. Can you help me a little bit? I thought if i only water the coco/plants after the coco dry out the ec would get a huge spike and this could burn my roots so i watered it daily in a 0.5l pot. You say only 100ml for the plants but would this not lead to root burn because the coco is too dry and this damage the roots?
    I was feeding an ec for my seedlings around 0.6-0.8ec that what the feeding chart said but i watered the complete 0.5L pot every day with about 2-300ml of nutrient solution.
    I did many grows on biobizz soil and want to try something different and use coco now and the information about coco is huge and every person/grower/Website says different things how to feed/water coco.. I got to a website and this guys feed their seedlings every day in the first three waterings and increase the watering to three time per day after week one?
    The seedlings have poor root development and slow to no growth. The website this guys also had very small plants and their plants were more than a month old.. My plants in biobizz were three time as big as their coco plants. I think that the problem is too much water for young plants/seedlings. But im not sure if it damage the roots if i let it dry out.. Cant find any article about growing in coco which are right because everyone says different thinfs about growing in coco coir.. My humidity/temperature is dialed in because i did grows in soil for long time so the problem must be with my watering practice in coco or the nutrient strength i use for my seedlings.

    1. Tim Alchimia

      Hi Crip, thanks for your comment and questions. Yes, you’re definitely watering too much which will have negatively affected root development due to lack of oxygen. The idea is to have only a bit of runoff each time you water and to allow the substrate to dry out a little bit between waterings, but not to have it dry out completely, there should still be moisture present when you water again. it’s an equilibrium, if the roots get too dry it will damage the plant but remember that if the roots are constantly waterlogged they can’t grow and will quickly rot, leading to poor plant growth and eventually death of the plant itself.

      Personally, if I was using a 0.5l container I’d be watering around 50-100ml each time and increasing the frequency of irrigation if I saw that the coco was drying out too quickly. You really need to observe the substrate properly and act accordingly, rather than watering a set daily amount regardless of the condition of your coco and the plants. Watering seedlings too much too often is a common mistake, when plants are small they don’t drink or eat anywhere as much as when they’re fully grown, so irrigation amounts and frequency will need to change in relation to development. If it takes more than 2-3 days for the substrate to dry out then you need to decrease the quantity of nutrient solution and conversely, if you see the plants are drinking it all up in a day, you can increase the amount or the frequency. I hope that helps, all the best and happy growing!

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