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MIX POTTING MIX

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Coconutty Coir

 For a couple of years, a block of coir has sat atop my bale of peat moss.
    Peat moss, the product of slow, anaerobic decomposition of organic materials, accumulates, at a snail’s pace, in bogs: an inch or so depth per thousand years. To mine peat, the bog must be first drained. Besides upsetting bogs’ unique ecological habitats, draining  the bogs aerates them, sending some of the carbon wafting into the air.Peat and coir
    But peat is good stuff for potting mixes. My mixes are made up of equal parts peat moss, soil, compost, and perlite, along with sprinklings of soybean meal (for nitrogen) and kelp (for insurance against lack of any trace elements). Peat’s contribution to the mix is a long-lasting source of organic matter that helps cling to moisture and to nutrients, important in the relative confines of a flower pot.
     Coir is marketed as a substitute for peat in potting mixes. A sustainable substitute, made from the fibre left around coconut husks after they’ve been cracked open to remove their meat.
    This spring it was time to put that block of coir to the test, with a head to head comparison to peat. (I’ve tried this comparison before, but more casually.) The block, after slurping up a large volume of warm water, was ready to mix with the same ingredients as I mixed with the peat moss.
 

Some potting soil components

Some potting soil components

   Both mixes went into their separately labelled , 5 gallon buckets. Each mix then was used to fill one-half of a few GrowEase Seed Starter Kits. Into one of the kits went lettuce seedlings, another got tomato seedlings, and a third got pepper seedlings. The 24 cells of each kit are automatically watered via a capillary mat that sits atop a water reservoir, providing very uniform moisture to all cells within a kit and from one kit to the next.

Peat, Coir Standoff

    Drum roll . . . and the winner is . . . well, as I recently wrote, some of this year’s seedlings grew very poorly, perhaps, I’ve hypothesized, due to the soil I used, or the compost, both of which vary some from batch to batch. The overcast, cool conditions in the greenhouse during critical growth periods also could be to blame.
    Differences in growth between coir and peat based mixes were not great, but tipped slightly in favor of the peat based mix. This, incidentally, jives with my previous, more casual observations. It also jives with more rigorously planned and executed, published research.

Coir Still in the Ring

    The results of all this testing don’t spell continued destruction of peat bogs. Coir might still be a viable alternative.
    Peat and coir are not the same material. I perhaps should not have used the same ratio for coir as I’ve long used for peat in my mix. There’s some evidence that coir, as it slowly decomposes in a potting mix, can suck up nitrogen at the expense of plants. If so, more soybean meal in my mix could solve that problem. Other nutrients, or lack thereof, could also come into play, as could anti-growth factors, such as phenolics, known to be present in coir.
    More playing around is needed with coir.

Peat and Coir Substitutes

    No need to put all our eggs in one coir basket. Other organic materials can and have fulfilled the niche of peat (and coir). And our culture has no lack of organic “waste” products. Composted bark has been used in commercial mixes for many years, as has sawdust. More exotic, around here, at least, would be rice hulls.
    Home-grown and readily available “organics” for a potting mixes would be compost and leaf mold, both of which I’ve used in rougher mixes, such as for temporarily repotting small trees.Mixing potting soil
    The point is that any of these organic materials, including coir, could make a good potting mix if ratios and amounts of other materials are adjusted accordingly.
    Gardening (and farming) should be, and could be, sustainable; even the potting mixes used to raise seedling or grow potted plants.

Now Perlite, Hmmmm

    The other major component of any potting mix is some aggregate, for providing good drainage. My mixes use perlite. Not sustainable. More on that another time.

A Reel Mower, Potting Soils

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Coming out of the gate of the warmest and driest winter in decades, weather this spring has been a roller coaster ride. March had a spate of sunny days in the 70s, then temperatures plummeted to the low 20s, then the dry spell was ended with some rain, and recently temperatures have continued on the seasonably cool and cold side. Lawngrass has enjoyed the weather, and during one of the recent calms I finally got the opportunity to roll out the lawnmower.


The opportunity!? Mowing the lawn isn’t usually one of my favorite pastimes but this spring I was anxious to try out my new lawnmower. No need to clean and tighten the sparkplug, check the gas and oil, and pray for  the roar of exploding gasoline (within the engine) with this new mower. It’s a push mower, “push” as in your pushing gets it moving and turns the front reel that lops grass cleanly as the sharp blades rotate pass the fixed bar.


Push mowers have come a long way since those heavy, iron monsters of yore and my new Fiskars Reel Mower was a joy to use. So much s that I was able to do a “Tom Sawyer” on my visiting brother and his two daughters, letting them vie to see who gets to create that musical whirring of the gears accompanied by a broad fountain of grass blades flying up and out in front of the traveling mower. (He ordered one for himself when he got home.)


Using a push mower is more than just fun, of course. It’s good for the environment. A gasoline powered lawnmower pollutes as much in an hour as a car driving 250 miles; pollution from electric corded or battery powered mowers depends on how the electricity is generated. A push mower offers the opportunity for productive exercise. And reel mowers make cleaner cuts than rotary mowers so result in a healthier lawn. I highly recommend Fiskars Reel Mower.
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A few weeks ago I fingered possible blame for poor seed germination and poor seedling growth on my having substituted peat moss for coir in my potting mix. Coir is a sustainable byproduct of coconut processing; peat moss takes eons to form so is not sustainable.


I’m happy to report that I was wrong. My seeding failures, it turns out, were due to the heating pad that is meant to provide gentle bottom heat for seed germination in my cool temperature greenhouse. Instead of the desired 75°F., the thermostat for that heating pad had been inadvertently turned up to 100°F (probably by me)!


Gardening brings into play the interaction of all sorts of physical, chemical, and biological system; the interactions are complex and this complexity makes it hard to ascribe cause and effect. But gardeners too often do this, just as I did (with reservations) relating coir in my potting mix to poor seed germination and seedling growth. 


To really find out if “A” causes “B,” (for instance, that coir is bad for seed germination) you have to control as many variables as possible (same seeds, same light, same watering, etc.) and then apply “A” to only half of your plants. It’s often not all that easy to control other variables. And anyway, if you start out believing that something — compost tea, for example — is going to make your plants grow better, you’ll be wont to not use it on all your plants. And then, if the summer happens to be sunny and warm with timely rains, you still might be inclined to tout that something — the compost tea, in this example — for good growth.
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My coir blunder did have the benefit of making me more objective about what makes a good potting soil. Many years ago, after much research, I came up with my own not-secret potting soil recipe of equal parts compost, garden soil, peat, and perlite with some soybean meal and kelp thrown in for extra nitrogen and micronutrients. Coir, in my last mix, substituted for all the peat.
After thinking that coir ruined my mix, I made up a batch of potting soil using 3 parts leaf mold (thoroughly rotted leaves) with one part perlite, again with some soybean meal and kelp. And then I actually did an experiment, planting half my lettuce seedlings in the leaf mold mix and the other half in the coir mix. Once removed from the overheated heating pad, seedlings grew equally well in either potting mix.


Which is to say, with reference to religions or potting soils: Many roads lead to the mountaintop. A good potting mix needs to drain well, hold moisture, provide nutrients, and provide a biologically friendly environment for roots. Perlite, sand or vermiculite can provide good drainage. Compost, peat, coir, or leaf mold help hold moisture and provide a biologically friendly root environment. Soil, compost, leaf mold, soybean meal, and kelp can provide nutrients. Various combinations of these ingredients make equally good potting mixes.