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!