Problems with Coir Based Compost Growing Medium

With a ban looming for peat based composts, home growers are increasingly trying out coir based composts. Many are hitting problems.

Commercial grower with potting compost

Commercial growers in the UK have until 2029 to continue using peat based growing mediums

I’ve had a number of emails recently about problems with coir based seed and potting composts. This email from a newsletter reader in Devon is a good example.

I tried this year to use coir instead of traditional potting compost that may contain peat. This was purchased as a compressed block and reconstituted by adding water to produce a wheel-barrow full.

I planted various seeds or small plants in it and all flourished initially but then rapidly died off, sometimes with blackened tips to the leaves. This ranged from pea and bean seeds to small plants like Mimulas that had self seeded from last years crop. The common denominator was the coir compost.

The same seed for peas and broad beans planted in traditional potting compost had no troubles at all.

Coconut coir, also known as coconut fiber, is a natural fiber extracted from the husk of coconuts. It is becoming a widely used substrate in gardening and agriculture, especially as a soilless growing medium and in seed and potting composts.

As a medium most home growers and commercial horticulturalists agree it is an inferior product compared to peat but as peat will become unavailable to amateur growers in the UK we’re going to have use alternatives or move to another country.

Problems with Coir

Contains sodium nitrate and chlorine

Coir also has high levels of sodium nitrate and chlorine, which can be harmful for plants if not flushed out regularly.

To flush out the sodium nitrate and chlorine from coir, you need to rinse it with plenty of water before using it. Some sources recommend using boiling water to dissolve and flush away the salts more effectively. Often this has been done at source before the coir is shipped here but not always.

Water Retention

Peat can hold 10 to 20 times its weight in water, while coir only holds an average of 8 to 9 times its weight. Admittedly coir can be easier to re-wet if it dries out but seedlings may well be killed by being dried out.

Coir based composts require close attention to ensure they don’t dry out and more frequent watering. This may cause problems as over-watering washes out nutrients.

Micro-Nutrient Deficiencies in Coir Based Composts

One issue with using coconut coir as a soil amendment is that it can tie up micronutrients like iron and copper. This means that these nutrients may become less available to plants growing in coconut coir based potting composts.

Iron and copper are essential micronutrients that plants need in small amounts to grow and develop properly. When these nutrients are tied up by coconut coir, plants may suffer from deficiencies. These deficiencies can result in stunted growth, yellowing of leaves, and other problems.

Some other micronutrients that coir may tie up are calcium and magnesium. These are essential for plant growth and development, especially for flowering and fruiting stages.

The reason coconut coir can tie up micronutrients like iron and copper is that it contains high levels of lignin, a complex organic polymer that is difficult for plants to break down. As lignin decomposes, it can release organic acids that bind to micronutrients like iron and copper, making them unavailable to plants.

Add amendments to coconut coir based composts to help release micronutrients.

To address this issue, gardeners and horticulturalists can add amendments to coconut coir based composts to help release micronutrients. For example, adding organic fertilizers that contain chelated iron and copper can help make these nutrients more available to plants. See below.

Commercial Flowers for Sale

The growers are under pressure to not use peat.

The ban on UK commercial growers using peat doesn’t come into effect for a number of years. However, the growers are under huge pressure from the retailers to have the magic words ‘Peat Free’ on their products.

In part, it was to help the commercial growers cope with the deficiencies of coir that prompted S-Chelate to develop their micro-nutrient supplements using chelation.

Chelation keeps the micro-nutrients bioavailable at a wide range of pH levels in coir-based growing mediums.

For the home grower they have two products. S-Chelate-O Cultiv-8 which is an organically approved mix of 8 micro-nutrients designed as a supplement. The other product is S-Chelate 12 Star which is a complete fertiliser including the main macro-nutrients (NPK)

Posted in Allotment Garden Diary, Rants and Raves
29 comments on “Problems with Coir Based Compost Growing Medium
  1. Duncan Stewart says:

    I used Dobbies seed compost this year and have had the most embarrassing failure of my tomato, peppers and chillies, where they should be healthy 150mm minimum plants by now they are barely 50mm, I have had to buy plants to start my hydroponics.

  2. John Stokes says:

    I, like a few other folk, have been using coir compost for a while now, but find the coir lacking in growth nutients. I find that mixing coir with other things ie – worm compost/leaf mould as a 50/50 mix works well.

  3. Diana Hill says:

    I have been a gardener for more than 30 years and an allotment holder for 13. I have had my fair share of success and mishaps but the lack of growth or at best very poor growth of seedlings this Spring has been dis-heartening to say the least.
    Tomatoes, cucumbers, beans, peas and flowers such as Cosmos and Zinnia all slow to germinate and either appear to rot off or at best growth is stunted or slow.
    Common denominator; peat free compost and not just one brand. I have tried to make a bit of a compost mix myself and have stared a weak feed very early in seedling growth. More information is needed on peat free compost bags in my view, especially if earlier feeding is going to be required.
    Those seeds sown in compost left over from last year and stored in the garage are doing very well.

  4. Trevor says:

    Last year I attempted to grow bush tomatoes in two containers filled with half coir and half compost. One had coir over the compost while the other had compost over the coir. This was to see how the young plants developed in each medium. The containers were in an outdoor sheltered south facing position.
    I watered regularly using my homemade strong Comfrey brew.
    The results were spectacular. I had the best crop of tomatoes ever and even through November, I was harvesting filled trugs of fresh tomatoes.
    I will be doing the same again this year!

    • Lydia Brindley says:

      I have bought what they are calling professional compost comes in a white bag with no actual writing on it . It’s 50% wood ! . It’s the worst rubbish I’ve ever had the misfortune to buy . It’s retains far too much water n form quite a hard crust on the top . Lost so many seedlings n young plants because of it

  5. Richard King says:

    Should we really be using coir shipped from the other side of the world?

    • Peter says:

      No we shouldn’t it’s shipped or flown from Sri Lanka mainly which produces it’s own carbon footprint but unfortunately there aren’t any other like for like peat based mixes that are cheap and readily available

      • Scott Mason says:

        It’s not ideal, agreed. But we can’t keep destroying habits at a rate of knots we are by digging peat. I haven’t done the maths, but I reckon the release of carbon by digging peat is worse than digging peat bogs.

        Coir works great mixed 50!50 with other compost, castings ect. If anyone is having trouble with it straight like stunted growth, yellowing. Try flushing it through with water at half strength feed. Put plenty through, don’t worry, you can’t over water coir. They should be bouncing back in a few days. It can be problematic but once worked out can be a fantastic medium. I’d go 50/50 with compost and start feeding earlier.

  6. John Lockwood says:

    I hear that most coir comes from Asia, I would hardly consider that environment friendly. Most gardeners want to buy a compost that they can use without adding extra ingredients to make them suitable. Surely like most things it will just open up a black market for peat compost. Scientists and industrial suppliers, think again!

  7. Ros Griffiths says:

    If the branded compost businesses are to succeed, they’re going to have to remove/add whatever’s necessary to make coir or other peat replacements work.
    I can see us growers having to pay the price!

  8. Derrick Brown says:

    I have seen it in garden centers, but never bought any, there does seem to be quite a few of composts that are peat free
    But I have just bought 4 bags of Ericaceous planting and potting compost, (buy one, get one free) I’m using it for planters and pots and topping up last years pots and planting my tomato plants
    I give everything a good feed of this chelate feed
    This coconut stuff doesnt sound very good, but I am just a fair weather gardener
    I think maybe a bit more time before this becomes mainstream for gardeners, allotments
    I have a hotbin, so I use the compost from that just seive it and scatter it over the garden, same as from my dalek composter (but it takes longer to rot down in that

  9. Colin Harbisher says:

    For many years I have used DT Brown compost with good results. This year the results have been awful. The compost once watered turns into a solid wet lump and nothing seems to flourish in it. I then tried Miracle Gro but not much better. Noticeable in both composts are lumps of wood stones string and even a piece of wire. Whatever the quality of compost has deteriorated and my neighbour says exactly the same.

  10. Jen says:

    I use coir as bedding for my chickens! They add their nutrients/ fertiliser/ poop & they I compost it for a while, then it makes amazing compost!
    The hens keep down garden pests organically & make beautiful garden ornaments, with friendly personalities, & provide me with an amazing supply of fresh eggs!!
    Probably cracked!! Jx

  11. John Boulton says:

    I too thought I was doing great; using cocoa coir instead of peat. It even managed to kill my lettuces – which takes some doing (and chillis and tomatoes, and squash plants). This year I have gone back to peat and bingo – great plants doing well all round.
    It takes huge volumes of water to flush out the chemicals, mainly sodium, from coir. This is in an area of the world where water is desperately short! Really, to be honest, coir is a disgrace.
    I flooded some coir with distilled water, evaporated the water and found to my astonishment some cubic crystal in the residue – this was proven to be salt, plain, ordinary sodium chloride (I brew beer and can test for this sort of thing).
    What we need is a good local (UK) source of organic material that isn’t contaminated with weedkiller, that is sustainable, doesn’t come from the other side of the world, supports crops as good as peat and is of a comparable price. Could anything be more simple? It appears not.

  12. Azzam says:

    I struggled initially, but have it sorted now. The nitrite and calcium is put there to buffer the Coco. That’s how it’s supposed to be. Coco managed properly is issue free. Calmag issues are common, look to add greensand and use fulvic acid to smooth things over. I buy most of my amendments and fertilizers from greenhandorganic and no issues since.

  13. David Cooper says:

    I have used coir for the last 7 years. When it is hydrated it is a sterile substrate, with no nutrients. Its up to you to add these to your requirements. I add about 10% perlite, and up to 20% worm castings for seed mix.
    This year I have germinated some Shirley tomato seed, that was collected by my late father in 2015, they took 9 days to germinate, and have been planted out. If you use some of your own compost with coir you have the best of both worlds, and a cheap compost approx, £3.50-£4.00 for 70 litres.

  14. Linda Bond says:

    I have been using Dalesfoot multi compost. It is made from bracken and wool. It holds alot of water but dries and crusts on top.
    I have been adding sand and perlite to it, and this week been mixing in a third coir… Have not had time to test the results but feels good
    I have found large seeds have been germinating ok in Dalesfoot but any small seeds that are surface sown or any that take more than 14’days are totally failing. .. Very frustrated

  15. Theo Corfield says:

    Coir as a proportion of the compost mix is the way to go. Green waste multipurpose composts are good sieved and used to germinate seed. Or mixed with coir, leafmold, horticultural sand, compost combinations, for potting. Coir is a byproduct so although shipping it is not ideal, its better than using peat. There are some things we cant make/grow in the UK, so we have to import them.

  16. Caroline Parry says:

    When I hydrate my coir compost I add a watering can of warm water with seaweed feed in. This seems to be suiting my seedlings well

  17. says:

    Look into hair, fleece ect based compost, much better, they’re doing great stuff in Chile, see matter of trust Chile, and Scotland

  18. John C Stephens says:

    We know coir is inferior to peat but as peat is to be band its time to move on and find a growing medium that works.

    I have no problem with coir tho I only use it as a bulker to my home made compost and add home made liquid fertilizer when needed.

  19. Kshitiz says:

    I am a newish small scale gardner – experience from last 6-7 years and mainly grow ornamental perennials/annuals, but lots of tomatoes, courgettes, chillies, potatoes and cucumber – I seitched to peat free compost from westlands 3 years ago and I have seen no difference whatsoever.
    Not sure why UK is so obsessed with peat. I come from India, a farming and agriculture based country, and my grandparents had a prolific garden in India. They never bought compost but mixed home mad compost with manure and that’s it.

  20. Bill Taylor says:

    I bought some peat free compost from B and Q last year. Terrible stuff. Compressed down to a solid block after watering. Had no success at all.

    This year used John Innes with some peat mixed in. Great success.

    Not sure what to do for the future. Probably use my homemade compost with something mixed in. Maybe buy a supply of peat compost to tide me over, assuming I can find some at all.

  21. Clive Fenn says:

    It seems from the original post and many of the comments on this and other sites firms are selling stuff that is not fit for purpose yet nothing is being done to ensure that the product on sale is suitable for what it claims to be. The government has imposed this ban on amateur growers but is doing nothing to manage it and is instead allowing big business to make profits with no responsibility for their actions. Why are not trading standards following up this? What happens when commercial growers go peat free? Surely this is more of a problem than amateur growers.

    • John Harrison says:

      The ban (in the UK) only applies to amateurs – the commercial growers have until 2029. However, the pressure from the retailers to be ‘peat free’ (because they think it’s so green) forces many of the commercial growers to go peat free. Local nursery told me one of the commercial suppliers of plants to garden centres had such a high failure and reject rate they went bust this year.
      As for trading standards – the compost producers are actually trying hard even if they’re failing, but you prove it was their composts as against your poor technique. An easy out.

  22. Ash says:

    I was very enthusiastic about using peat free compost and purchased coir based compost. I had 2 malus crab apple tress delivered in March, from a reputable company I have used before. They were tall and strong looking specimens but they have really struggled. They just havent grown, when a blossom bud came out it shrivelled and died and there is no blossom and no leaves at all. The smaller tree is definitely dead now and the taller one, although still alive is pitiful- it just wont/ cant grow. I cant understand why this has happened. The only different thing I have done is use peat free coir based compost mixed in my soil. Has anyone else had any problems with planting trees this year?

  23. Peter Beviss says:

    I have used peat free compost for the last three years, trying various brands.Each year I found Sylva grow too be the best by a long way.I had great results with everything I grew in this compost.Follow the instructions on the bag, especially the one about over watering and carry out regular feeding and it works very well.

  24. mike wilding says:

    Hi John. I didn’t know where to put this on your site. I have 4 x 330l compost bins…using 2 each year. This year after digging my first runner bean trench I put roughly 90% of one bin, which had been breaking down for 18 months, into the trench. The rest I raked up and put into a couple of bags to dig into the soil where I shall be planting my tomatoes. I’m no soil expert but my guess is the soil under the bin must be full of nutrients which have leached into it from the breaking down compost. I dug up this soil, sieved it and used it for my runner bean and tomato seeds All have grown very well and are nice and healthy. One way to stop using peat/coir shop bought compost! Regards, Mike.

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