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

10 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!

  2. Crip

    Ok thank you ☺️ i will water them only with 150ml now. I have another question. I used canna coco before and i found the coco was too fine so i switched to ugro coco and i had no problems with the canna coco with germination. Only that i watered too often. I find the particle size with ugro coco better its more airy i would say. I start the seeds in paper towel method and after the root is 1/2cm long i transplant into the coco. But this time the seedlings had burnt leafs and i think it was the salt in the coco that causing the leaf burn. I hydrated the ugro rhiza and my hands started to dry out after i filled my pots with the coco. The only thing could be that its high in NaCl/sodium chloride that causing the burnt leafs and my dry hands after handling with the coco coir.

    What should i do so my seedlings dont get this problems the next time?
    Should i flush the coco with osmosis water and germinate the seeds?
    Should i flush it with some fertilizer and plant the seeds for germination into it?
    I think fertilizer in the germination is not good but i read if you flush the coco with pure water it will change the buffers and causing calmag deficiency in the early stage 🤔 not sure what i should do.
    I will try with some seedlings to find out if its the salt in the coco and will try to flush the coco with nutrients and germinate two seeds.
    Another two seeds i will germinate where i flush the coco only with osmosis water.
    And another two i use the coco without flushing and only water it to keep it moist

    The ec was 0.6 out of the bag/brick coco and i didnt flush just hydrate the coco and set the seedlings into the coco with a small amount of water so the seedlings have enough moisture.

    1. Tim Alchimia

      Hey Crip, thanks for the comment, it’s good to hear from you again. Yes, it sounds like you’re right and maybe the Ugro needs a bit more of a rinse than just simple rehydration, although I wouldn’t overdo it, as you may end up washing away the mycorrhizal fungi, which would defeat the object of buying Ugro Rhiza in the first place!

      I think your suggestion of trying a few different experiments to find the cause is a great idea and the best approach to properly understanding the problem.

      You may find that it’s only a problem during germination and the early stages of the plant’s life, in which case you could try thoroughly flushing a small amount of the Ugro coco, just enough to germinate the seeds and keep the seedlings going for a week or two in a small container, until the seedling is strong enough to handle a higher EC, when you could transplant it to the normal (un-flushed) re-hydrated Ugro. Alternatively, since you already know it works well for germination, you could use that for the early stage, transplanting to Ugro Rhiza for growth and flowering.

      I hope that helps, let us know how you get on, please. All the best and happy growing!

  3. Crip

    Thanks again 🙂 i will report how it went out. I have another question.
    When do you start to feed your seedlings? Should i give nutrients from the beginning or should i wait until they lose their colour?

    And how much fertilizer in ec/ppm should i add?

    My fertilizer says 1ml for seedlings/clones and this is an ec around 0.6-0.8ec. But i cant find if they mean from the beginning after they show their first leafs or cotyledons or if i should wait till they have one to three true leafs. Its hard to find detailed informations how to feed seedlings in coco or how to water the coco right because everyone use different methods. I will follow the watering guides you told me. I like your Website very much ❤️
    I want to make the best out of it. I had great results with biobizz soils and i want to get the coco grows as perfect as the soil plants. First i thought coco is like growing in soil and only i have to add fertilizer from the beginning and watch how the plants look and increase/decrease the feedings but its not as easy as i thought 🙂 but i want to work with coco and its fun to learn more about growing in different medium/soil or hydroponic. I will use coco now for some years and if i get the most out of it i will try some different hydroponic systems. Thanks again for your fast response and sorry for the bad english and hope you understand what i mean 🙂
    Greetz Crip

    1. Tim Alchimia

      Hey Crip, hi again! Please don’t worry about your English, it’s really great and I understand you perfectly!

      Those EC levels sound about right for seedlings. Normally, in soil, I wouldn’t feed seedlings till they had 3 sets of true leaves, but as you point out, plain water can be a problem in coco, so maybe cut the fertiliser dose in half for the first few irrigations, and see how the plants react before giving them the full dosage.

      As far as the watering goes, too much will cause as much of a problem as not enough, so aim for about 20% runoff each time, that ought to be enough to flush away any excess salts without causing problems. But remember that there’s really only so much you can learn from a guide or instructions. Conditions will differ from growroom to growroom, and everything from the genetics being cultivated, to the temperature and the humidity, will affect the plants’ demand for water. This means you’ll need to be reactive to what the plants are telling you, at least until you get your particular grow space and genetics “dialled in”. It seems to me that you’re going about this the correct way, by analysing any problems and doing a bit of experimentation until you find out what works for you.

  4. Crip

    Hey Crip again i have some more question and sorry for all the questions.
    Advanced nutrients coco fertilizer says to add 1ml/l for seedlings and maybe i added the fertilizer too early? I thought the seedling stage begins after the seed germinate and open the cotyledons and i didnt got an answer back from advanced nutrients. So maybe the burn came from the fertilizer.
    And another thing that maybe caused this burning was the flushed out coco buffer and maybe the ec 0.5 in the ugro coco is the calmag buffer. I used the 500ml pots and added about 1-150ml of nutrient solution and it drained really quickly, and the chloride gets released if you wash out the buffer and the nutrient solution goes into the coco and the calcium Magnesium gets bond to the coco because of the CEC in coco. At the website from canna coco they have an article if you flush the coco without nutrients or too low nutrients you will wash away the buffer and calmag deficiency starts.
    Really hard to find out what the problem is, maybe the fertilizer added too early, the buffers washed away and released the chloride. Today the plants show signs of a calcium deficiency on their first leaves, small brown points in the middle of the leaves, the head lookin yellow and a little twisted.
    Maybe it is the Advanced nutrients fertilizer because the coco fertilizer only contains 3.5% calcium and all other coco fertilizer has up to 5% of calcium. The fertilizer must be used with osmosis water because only with osmosis water the ph perfect works 🤦 i tried tapwater and the ph was waay too high and advanced nutrients says you should not adjust the ph or you will get more problems.. I thought this fertilizer is simple like they say on the website..
    I have some more seeds germinated yesterday and i did put them into the coco some hours ago.
    2 seeds i only gave them water without nutrients about 75ml in the 500ml pots, 2 seeds i did flush the coco with nutrients until the runoff had the same ec 0.6 of the Advanced nutrients fertilizer and put the seeds into the coco. 2 seeds i added only 0.5ml/l fertilizer and also flushed the coco and put the seeds into it, and two more seeds i added fertilizer but i dint flush the coco only 75ml of nute solution.
    Dont know why the other seedlings show now signs of calcium deficiency but advanced nutrients says dont use calmag or it will change the ph perfect and they say the base nutrients have enough calcium in it.

    You should make an article about starting seeds into coco and how to feed them, how much water that would be so great. I cant find any good article. One Website says feed three times per day after the seedlings germinated and add fertilizer between 0.4-1.2 ec. Others say flush out the coco before set the seedlings in it and start to feed after one or two weeks… Never saw so many different opinions how to grow seedlings in coco coir 😕 or maybe im just to stupid to understand how it works..

    1. Tim Alchimia

      Hey Crip, don’t worry about the questions, we’re here to help if we can! I can’t comment much about Advanced Nutrients products as we don’t sell them here at Alchimia, but I can fully sympathise with all the conflicting advice and contradictory instructions, I don’t think it’s a case of you being too stupid to understand it at all! It all reminds me why I chose to grow in organic soil and pretty much forget about EC and pH levels!

      In this case, I understand you’re concerned you may have washed away the buffering, but given what Advanced Nutrients claim about their products I honestly don’t know if it’s a good idea to add any calmag to see what happens, to see if that rectifies the situation or not. They are quite specific about calmag not being necessary, so I don’t want to recommend it.

      Anyway, that’s a great idea about a post explaining germination and early feeding in coco, I will look into it, thanks. All the best with this project, you’r certain to earn a great deal from the experience. Happy growing!

  5. Crip

    Thanks mate 🙂 i didnt add calmag to the Advanced nutrients fertilizer and i did feed some seedlings with 2ml and they look more green. The other seeds still have the yellow top and some brown spots between the margins. I was on the ugro Website and found a article how they buffer the coco coir and how to use it if i hydrate the brick. I will copy it in the comments:

    1. Washing in fresh water, dragging a large part of the salts by dissolution
    2. Chemical buffering
    3. Second washing in fresh water, dragging by leaching a large part of the salts resulting from chemical buffering.

    The result is a substrate with an EC of 0.4 mS/cm in a measurement of 1 volume of substrate in 1.5 volumes of water.

    Even after this process, the decomposition of coconut organic matter releases sodium salts, so liquid fertilizers for coconut carry a calcium reinforcement in the formula so that there is always available calcium.

    To use this type of substrate it is recommended to start the fertigation with an EC level of 1 mS/cm and rectify if necessary. An excess of fertilization could lead to an excess of calcium, which would produce a chemical block of iron, the result of which would be a radical stop in the plant’s growth and severe deficiencies in a short time. If this occurs, the plant should be spray with chelated iron and the EC level should be lowered below 1 mS for one or two irrigations.

    After the buffering they wash it with fresh water and i think if you would buffer with calcium the coco absorbs it and release the potassium/chloride in that buffering solution. And if they wash it down to 0.4ec the salts would be a mix of the buffering solution and most would be NaCl/potassium and maybe thats too much NaCl for the seedling, but im not 100% sure and they say to start feeding the coco with an ec of 1.0 and i only used 0.6ec what the Advanced nutrients says on the bottles.

    I think the guys from ugro know it better how their coco works and what ec to add so you have enough calcium for the plants. But they say if the ec of 1.0 is too much calcium toxicity occurs and the plants stop growing and get a iron deficiency and decrease the next two feedings🤔 my seedlings only have one true leave and the second is light green and still no real growth with the most seedlings. And i think i cant say if its a calcium deficiency or toxicity 🤔 but i didnt start feeding with the 1.0ec so i think its a deficiency.

    The seedlings i water with 0.6ec like advanced nutrients say have the lime green heads, the other seeds i use only 0.3ec to see if they grow faster but they are the slowest and the other seedling i use 1.0ec and they dont have the lime green head but still growing slow 😕

    I think i will give them all the 1.0ec and hope they dont get a nute burn later, the ec sounds really high for seedlings and i also asked them if i should use 1.0ec if i plant seedlings into their coco, and if i should wash out that 0.4ec salts with the nutrient solution at 1.0ec or only water the pots a little and dont care about the salts in the coco.
    Canna coco says with their fertilizer and their coco you must add 0.6ec of their coco fertilizer because of the buffers and normal you use tapwater with this nutrients so the ec would be also around 0.9-1.0 if you add the seedlings in their coco n and the coco nutes.
    I also dont feed until the coco lookin light brown on the top and i hope the seedlings just build their root structure in the coco and will give me fast growing plants in some days.

    Would you add an ec of 1.0 like the guide from ugro says even if you put the seedlings in the coco? 🤔 Dont know how much salts or ec a seedling can handle and dont get burnt or grow slow because of too much fertilizer.
    If you write an article about how to start seeds in coco i really would love it. I read every article the next weeks and keep up the good work and thanks again that you always write back and i will comment the next days if something has improved or if the plants are still lazy 😁

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