Peat-free Planting Mix Recipe With Coconut Coir

Nancy’s coconut coir-based planting mix. Here she’s doing the squeeze test, which we talk about below.

From an environmental perspective peat moss is a nightmare. Mining of this material is unsustainable, contributes to global warming and destroys habitat for many plants and animals. But, for starting seeds, we’ve used it for years. Our friend Nancy Klehm taught us recently how to make a seed starting mix with coconut coir instead of peat moss. Thanks, Nancy! Here’s how to make it:

Ingredients

Watering the coir brick to break it up. Once saturated, this brick will expand to fill the tub.

COIR:  A fibrous material made from coconut husks. It is sold in compressed bricks which expand greatly when wet. It is pH neutral and has no nutrients. Its role in planting mix is to hold moisture. Coir is the environmentally correct alternative to peat. Peat is mined out of peat bogs, which is a disruption of an ecosystem. Coir, meanwhile, is a by-product of the coconut industry. Of course, it has to be shipped in from the tropics, so is not particularly sustainable in that way. Nothing is perfect. So, if you have peat on hand or prefer peat you may use it in this recipe instead of coir, just substitute it, 1:1.

PERLITE: Perlite is a volcanic glass which, upon being subjected to extremely high temperatures (850C +), puffs–sort of like popcorn, or a Pop Rock. Obviously, though its origins are natural, it is an industrial product, but it is very useful for making soil fluffy and light. You will recognize it as the “white stuff” that you see in the soil of nursery plants. As it is essentially a rock, it is a neutral player in the mix. It simply keeps things light.

Note: you should avoid breathing perlite dust when working with it.

Store-bought worm castings. Homegrown, of course, are the preferred alternative!

WORM CASTINGS: Castings bring healthy microbial activity to the mix, as well as balanced nutrients and trace minerals. In addition, they hold moisture well. They are invaluable players in this mix. You can buy worm castings at the nursery, or you can keep a worm bin and harvest your own. Store bought and homegrown castings have very different textures–the store bought tends to be very fine, almost a black powder, whereas castings fresh out of the worm bin have more of a open, grainy, soil like texture– and this effects the recipe.  

For the purposes of this recipe, we will assume you are using fine-grained, store bought castings. If you have your own castings, congratulations! But you will have to play with this recipe a little bit. You will use a little less coir, because your castings (probably) have loft or springiness of their own. We can’t tell you exactly how much less coir, because castings vary.  Start, say, with half the recommended quantity of coir in the recipe below, and then test the mix, and add more coir as necessary. The proof will come in the squeezing. Do the hand test described in the instructions below. If the mix won’t hold form when you squeeze it, you have too much coir, if the clump you make doesn’t break easily, there isn’t enough. Again, see below.

Quantity

This recipe makes about 4 gallons of planting mix. To make more or less, just use the same ratios. 

Equipment

We like to mix ours up in 5 gallon bucket, but you can do this on a tarp or in a wheelbarrow or whatever you like.

You will also need something big, like a cement mixing tray or tub to soak the coir brick in. Remember, one brick swells into to a big bag’s worth of wet coir. If you don’t use all the coir, you can store it in a plastic bag. If it dries out, it can be re-hydrated.

You will also need a measuring tool. For this 4 gallon recipe you will need a quart measure to scoop the materials out of the bags–like a big yogurt/cottage cheese container, or something with same volume. Again, you can make as little or as much as you want using the same proportions, so your measure could be a 1 cup scoop or a 3 gallon bucket.

Prep

Prepare to make the mix by soaking the coir in a large tub of water for maybe a half hour or so. Break it up as it expands. It will drink up a lot of water and grow proportionately huge. Add water if necessary so that it all gets evenly moistened. When finished, it should be wet but springy, like a wrung-out sponge.

Put it together

3 quarts/parts worm castings (store bought, see notes above for homegrown)
8 quarts/parts coir
4 quarts/ parts perlite

Measure out the worm castings and coir into a five gallon bucket and toss them together with your hands until they are evenly and thoroughly mixed. This mix should be moist and dark, again with a nice “wrung-out” sponge level of dampness.

Only when those two are mixed should you add the perlite. It’s easier to mix the perlite in last–trust us. Mix the perlite into the coir/casting blend until it is also evenly distributed–the mix should be absolutely consistent–no patches or clumps should be visible. You might find it helpful to dump the mix back and forth between two five gallon buckets to speed mixing.

After it is mixed, pause to analyze the texture. Gather up a fistful, squeeze it hard and open your hand. The mix will form a ball in your fist, but if you turn your hand over and drop the ball a few inches, it will break easily. Overall the mix should be moist, light and springy. We can’t emphasize that enough. Moist, but not soggy. Springy, not heavy.

If the mix seems a little clumpy/dense/heavy don’t be afraid to add another part of perlite. It is better to err on the side of too much perlite than too little. Lightness is everything.

Measuring into the buckets with a quart-sized yogurt container. If you have two buckets, you can pour the ingredients back and forth between them to speed mixing. Otherwise, just toss the ingredients with your hands in one bucket.

Notes on growing

The seedling feeds itself from its seed body up through the formation of the first set of leaves, the cotyledons. After that, it is dependent on the nutrients in the soil. Your seedlings will be fine in this planting mix until around the time of the full unfurling of their first true leaves (the ones that come after the cotyledons). At this time–or no later than the opening of the second set of true leaves–you will want to feed your seedlings by watering them with some kind of diluted organic fertilizer of your choice. Do this maybe once a week until you transplant them.

Feeding accelerates root growth which is even more important to plant health than leaf growth. It prepares the plants to thrive after transplanting.

For most seedlings this means the first feeding would occur about 3-4 weeks after planting. The seedlings should be transplanted by 6 weeks of age–either into the garden or into bigger pots with real soil.

Recycling

You can re-use this mix to plant more seedlings, but you’ll want to recharge it by adding in more worm castings. Just dump out your seed starting trays, mix it all up and let it air a bit. Also, the coir breaks down over time, so you find you need to add more of that as well. And if you add enough castings and coir, you’ll probably want to add more perlite to balance it. There’s no recipe–you’ll have to use your intuition to create a consistency that resembles the original mix.

Or you could compost it and start fresh. It’s safe to compost perlite, as long as you don’t mind having little white perlite bits all over your yard!

This is the surface of the finished mix. It’s so light and moist that it has holes in the surface. Note the even integration of the three ingredient: no lumps or patches left unmixed.

Options
 
Another planting mix option is part coir and part compost. This is provided your compost is of the best quality–bagged compost from the nursery is not good enough. This is a hard area to generalize about because compost varies wildly in both quality and consistency, but you’d want to use lovely, lively, springy, sweet smelling compost.

Gardening guru John Jeavons starts his seeds in mix which is 1 part compost and 1 part garden soil–soil dug from the same beds the seedlings will be going into. This way the seedlings are already accustomed to the local soil and don’t go through so much shock upon transplanting. It also makes his garden a “closed loop,” meaning he doesn’t have to buy anything or bring any materials in from the outside. This saves money, keeps things local and prevents the accidental importing of diseases.

Using compost and soil works for him because he’s got top-notch compost and rich, fluffy soil–the kind of soil you can plunge you hand into up to the wrist without meeting resistance. This should be a goal for all of us to work toward, but in the meanwhile, while we’re developing that soil in our own yards, we’ve got perlite, worm castings and coir!

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23 Comments

  1. I’ve tried peat moss mixes a few times, but I greatly prefer the texture of coir for seed starting. This recipe is similar to what we use at home and work–a 3:2:1 coir-castings-vermiculite combo. Personally, I don’t love using vermiculite or perlite at all. I’ve experimented a bit with a 2:1 coir-castings mix that I think could work, but it would obviously be more expensive. Trial and error!
    -Megan

  2. So, I had read at one time that the sustainability problems with peat moss were due to people burning it for fuel, not due to agricultural uses.

    I can’t remember where I saw that info now though…

  3. I love making soil blocks with coir, but for much of North America it’s an imported product. Still trying to come up with a local alternative.

  4. Thank you for this! The cost of the little bags of seed starting mix has started to add up, and I’ve been thinking about how to scale up my seed op without that expense. I’ve also been thinking about the need for fertilizer for the seedlings that have been around for a while, so thanks for that tip, too!

  5. Have been successfully starting my seeds in plain old potting mix for years now. Someone gave me some coir and it made my hands itch, so that’s out and have never really found any difference in seed starting with regular potting mix vs seed starting mix, so . . . .

  6. Hey guys, glad you hopped on the soiless building wagon! I would have a few more tips for you.

    Always check the ph of your mix when you’re done, the humates in the castings help balance it out and give a buffer but they may not be enough by themselves which is why every good soiless mix should include…

    Dolomite lime! DL is an awesome additive in the fact it not only balances out ph around 7 without going over but adds calcium and magnesium to the mix, two often over looked nutrients. About 1 tablespoon per gallon of mix should be fine. For the beginner gardener I must stress that there are many types of lime. No substitution will do, it must be dolomite lime. Make sure to get the powdered NOT the pelleted DL. Again, no substitutions.

    Another very important additive to consider is Mycorrhiza fungi. Myco binds to the roots of your plants and greatly increases their surface area while adding resistance to soil borne pathogens. More root surface area = more nutrient and water uptake = huge happy plants.

    When mixing up my organic soiless mix I like to stop at this point and set enough of the mix aside for my seedling needs and continue on with the rest of the mix by adding in organic ferts. This way I don’t have to feed my peppers, tomatoes or eggplants…. ever. Being organic gardening I like to use the ole fallback, poop! Bat G guano to be specific. I use about 1/4 cup high nitrogen guano and a little less high phosphorus guano for every gallon of mix. I also add a tablespoon of kelp meal. Kelp meal is an organic source of potash and is chocked full of plant growth hormones. Make sure your mix is slightly moist and let this sit for four weeks so the microbes can go to work processing everything to make it ready for planting. I should stress that this mix is NOT for seedlings as it’s too hot (rich) and will burn them to a crisp.

    Whew, not done yet.

    When you’re watering your organic potting soil you’re not feeding the plants, you’re feeding the microbes in the soil which in turn feed the plants with their poop. If the tap water in your city uses chlorine (or an even more evil version called chloramine) you’re not doing your plants any favors by killing off your micro herd. A solution to this is to fill barrels or five gallon buckets with tap water and let them sit out for 24-48 hours. I bubble mine with a small cheap aquarium air pump and stone. This will only work if your city uses chlorine and not chloramine. Chloramine is a combination of chlorine and ammonia that does not dissipate and is rather toxic. My city uses this so I try to use rain water.

    as for mixing large amounts of mix you can invite a friend over to help you mix. Just throw the mix onto a large tarp and each of you can grab a side and rock it back and forth. This quickly mixes everything up.

    If you’re more of a loner or have back problems you can always rent a cement mixer, clean it out thourhoughly and use that to mix batches. Just dump em in a kiddy pool as you go.

    It should be noted that any soiless mix should be set to the side and given a few weeks to “cook” before planting.
    Okay, I think I covered the basics. Hope that helps!

  7. Have you had any issues with salt in the coir? I suggested it once to my friend as an alternative to peat moss (which is ironic beause he was the first to tell me about its unsustainability.. I guess he just couldn’t live without it), and he replied that he doesn’t use it because it’s been known to be salty stuff, which some of his plants can be very sensitive to. Any thoughts?

  8. Mjai,

    I had heard about salt issues as well. The coir I bought is labeled for horticultural purposes–I got it at our local nursery. The salt issue is primarily with low quality coir. I’ve planted seedlings in this coir mix and they seem to be doing fine so far.

  9. The coir blocks sold by Gardener’s Supply Company (gardeners.com) in Vermont have had the salts removed and are pH balanced. Periodically the company offers free shipping, so it’s worth being on GSC’s email list. If you’re going to be in or near Burlington though, it’s a really fun place to visit.

  10. Salt can be removed from coir by rinsing it very thoroughly. People can say what the want about peat but when it’s harvested responsibly it is a sustainable product. Coconut coir has to be processed and shipped in from areas where they grow and process coconuts so it has a comparable carbon footprint.

    Really it’s just about whichever lets you sleep better at night. Another note on coir, it really soaks up and holds nitrogen so be careful if you feed with liquid nutrients in it.

  11. Hmm, now off to find coir that doesn’t cost $5 a brick from some pot growing hipster. When coconut refuse can be bought for what it actually costs rather than as a medium for growing pot and making tons of money than I could accept it was a substitute for peat.

  12. I am starting seeds this year (for the second time, but last year didn’t go well). I want to try this and I just harvested some of my own worm castings. Do I need to be worried about the worms and spider mites (there are a lot) and food scraps (small) that came along for the ride? It was my first time harvesting the castings and I’m not sure I did a good job.

  13. @Theresa:

    That’s a hard question to answer without seeing the castings in question.

    There shouldn’t be spider mites in worm castings–spider mites eat living plant tissue. What would they eat in a worm bin? I wonder if you’re not seeing these teeny tiny little beetles that move into worm bins sometimes. I can’t think of their name just now. In sunlight, they are very coppery and they’re about the size of a pin head. They are nothing to worry about (I think they tend to show up when there’s too much newspaper and cardboard, but that’s just my theory). At any rate, they don’t hurt anything, they are just a part of the cast of characters that moves through the bin. But I’ve never seen them in finished castings. By the time castings are finished, there’s nothing left for them to eat at that stage.

    If you do have those little beetles in your castings as well as small food scraps, I’m wondering if your castings are not quite finished. There should be nothing that looks like food in there except maybe egg shell bits or the occasional indigestible rind. If I were you, I’d dump all of that back in the bin and let it age some more.

    Re: the worms, they won’t hurt anything if a few end up in potting mixes, etc., but it would be much better to pick them out and toss them back in the bin, so they can live on.

    If I’m wrong about the beetles, and you really do somehow have spider mites in your castings, then I wouldn’t use those castings to start seeds. You’d be better off just buying a bag of seed starting mix at the nursery.

    Hang in there! Good luck with your seeds this year.

    • I don’t have the book for reference but I remember reading about spider mites in worms eat my garbage, so that is what I always assumed them to be. They could easily be something else. They are tiny, pin head size is about right, white, and they burrowed in the pile when I dumped out my bin. They also seemed to jump around, kind of like fleas.
      I’m curious how to finish my castings. I did a dump and sort method of harvest. I tossed most of what was identifiable as food (and with it a lot of castings) back into my bin (along with all the worms I could gather). My bin still has a ton of material in it. Is there a better way to harvest? Should I leave the bin alone for months before I harvest and start another in the mean time?
      Thanks for your help!

    • Interesting about the spider mites–I’ve never seen them in my bin. I definitely would not want them in the planting mix. They should go away by the time the castings are really finished.

      If you can, shove the unfinished stuff, or most of it to one side and put fresh bedding on the other. Feed only in the fresh bedding. The worms will finish up the old stuff and make their way over to the new side over 2 or 3 weeks.

      To get worms out of the castings, spread a tarp outside during daylight hours. Make several largish softball sized mounds of the castings. The worms in them will dive to the bottom and center to get away from the sunlight. After a half hour or so, you should be able to take a handful off the top with no worms in it. If not, wait a while longer. They’re slow.

      If the mix is really wormy, they’ll all be in a ball at the bottom. Toss them back in the bin. Keep doing this til you have as many castings as you need. Be careful if it’s hot and dry out because you don’t want the worms drying out or baking. An alternative method is to make a big pyramid of the castings instead of several softballs. Harvest from the top, reform it, come back a while later, harvest some more, reform, etc. They’ll keep diving down to the bottom.

  14. I used these instructions to mix up some seed-starting mix last weekend, and just yesterday noticed the first green shoots coming up! (Calendula, which I was inspired to plant thanks to reading your blog.) I got so excited, you’d think I’d invented something instead of just observing a phenomenon that’s been happening for thousands of years without any help from us whatsoever. I’m starting the seeds inside and using a heat mat and desk lamp for extra light, but I’ll bet that great starter mix had something to do with the quick germination. I did use peat instead of the coir because I had some on hand, but will look forward to trying the coir in the future. It was very exciting to use my own homegrown castings for the first time too. Thanks for this very useful post–it will be a permanent part of my garden recipe file!

  15. Thank you, thank you, thank you for touching on the subject of harvesting peat moss and it’s effect on the environment.

    I posted about it on my blog — The Sustain Blog — ages back with a link to a post on Garden by Ken Druse talking about the environmental harms of peat moss.

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