Part 1 of: The Growing-Media Dilemma

Part 1 of: The Growing-Media Dilemma

Friday, January 27, 2023

On peat, coir and staying local

The summary:

  1. A lot of experts, especially ones based in the UK and Europe, are discouraging the use of peat in potting soils
  2. The challenges faced by ecosystems vary in different regions of the globe
  3. Peat harvesting has taken place at a very different scale, and for different reasons, on this continent than in Europe
  4. Of the large land-mass ecosystems on this continent, peat bogs are under less threat than most others
  5. Extracting from distant ecosystems isn't a good alternative
  6. Focus on using less, rather than just using something else.
  7. Compost

Jump to Part 2 to read about my (current and still evolving) approach to providing seedlings with the growing media that they need to thrive while keeping the ecological cost to a minimum.

Or read on for Part 1 - The long version:

The calls to grow plants in peat-free potting soil (growing media) have been increasing, especially in publications and media originating in the UK. There is good reason for this, peat moss is a slow to regenerate carbon sink and even restored peat bogs (when the living sphagnum moss and plant layer is replaced at the top of a harvested bog) continue to emit carbon at a faster rate than they sequester it for years after they are restored. Peat bogs in the UK and through western Europe have been mined for use as a fossil fuel to such an extent that they are threatened at a scale similar to the threats to old-growth forests on this continent, with only 1 to 2% of their pre-extraction extent remaining in many areas. Like old-growth logging here, all of the extraction from western European peat bogs needs to stop right now.

Where things start to get a bit less clear cut is in ecosystems outside of western Europe and when the question of what we should be using instead is asked.

In growing media, peat moss behaves like a sponge, holding water in a way that is easily available to roots, while also allowing excess water to drain away, preventing anaerobic conditions and the diseases associated with that. Due to the high acidity conditions of bogs, peat comes out nearly sterile, minimizing the potential for fungal and other diseases, and generally nearly or entirely free of seeds. All without any heat or chemical treatments. These are valuable traits for plant propagation and growth in contained settings.

When evaluating alternatives, the starting criteria is generally carbon rich organic matter with a fibrous texture, to provide a similar water-holding yet free-draining environment for root growth.

Coir, the coarse fiber in the thick husk that surrounds mature coconuts, is probably the most widely promoted, and available, direct substitute for peat. It is produced by stripping the bulky fiber and pith layer from coconuts and retting these husks (soaking them in water) for a few months to soften and wash away the pith surrounding the fibers, which are then dried and milled to the desired texture. There is also generally some treatment involved to manage their naturally high levels of sodium and potassium. The specifics of the treatments vary between regions and producers. One of the concerns raised about coir is water pollution at the retting stage. When done at a small scale, to support local use, the local ecosystem generally has the capacity to break down the materials and (naturally occurring) chemicals that leach from the husks, the problems occur when production is scaled to serve a large market, like the global demand for potting media. At this scale, water pollution becomes a significant issue. Worker safety, relating to the inhalation of dust during the dry stages of the processing, is also an area often highlighted as being of concern. Especially in areas with few, if any, worker safety regulations.

Even with these challenges, coir could quite likely be viable growing media in and near the regions where coconut trees grow, especially if it can be cycled back into local soils once it has decomposed beyond the point of being a viable potting medium.

Where is becomes less viable is when/if production is scaled up to the point of supplying the current global demand for growing media. A lot like palm oil, which has long been a valuable calorie source for the people who live where it grows, when production is scaled up what was once sustainable quickly becomes entirely unsustainable.

Extraction of organic matter from tropical ecosystems and shipping it long distances will always be an ecologically and socially fraught undertaking.

Composted bark, either shredded or chipped, is another option, popular for container grown trees and shrubs, but it is generally a bit coarser than is appropriate for small seeds and seedlings. There is also the unfortunate reality that forestry practices in Canada are at least as rife with sustainability limitations as peat harvesting, with disturbed forests emitting carbon for years following disturbance. Practices like clearcutting, replanting with monoculture species and broad scale glyphosate (Roundup) spraying are also linked to increased fire risks, pine bark beetle pressures and other disease issues. Large swaths of cutting also contributes to increased down-stream flooding, both due to decreased capacity to absorb rain where it falls and increased rate of spring snow melt, due to the loss of shade. Add in the issues around forestry roads not being fully decommissioned, leading to increased predator pressures on forest dwelling grazers and limited capacity for root and mycelium system regeneration, and the forests of this continent are under even greater pressures than the peat bogs. (Finding the Mother Tree by Suzanne Simard offers a good overview of these pressures, and some of the things that can be done to shift current forestry practices.)

The other large source of organic matter in the Ontario horticulture industry, mostly in the form of manures and straw, is agriculture. On its own, manure is too dense and prone to water logging for most container growing. Chopped straw tends to be prone to mold growth when kept consistently wet. Fine in many outdoor settings but not ideal for use as an indoor growing medium (there is some experimentation going on in the use of Flax and Miscanthus as sources of organic matter for growing media that may lead to some additional options in the future). Ideally, composted manures are returned to the soils where the feed that they came from was originally grown to help preserve their fertility and biological health. Agricultural soils in this country were losing 21 megatons of carbon every year as of 2020. Extracting more organic matter from these systems isn’t sustainable either.

The environmental footprint of growing medium also isn’t limited to the organic matter portion. Vermiculite and perlite, both of which are commonly added to growing media, are mined materials and are expanded using heat from fossil fuels. Sand is dug from large open pits.

Of the large perennial ecosystems on this continent, peat bogs are the only one that I know of that is being extracted from at less than their regeneration rate, given how extensive they are (12% of this country’s landmass) and how much of that has been harvested (0.02%). This is a different situation than peat bogs on the European continent, where peat has long been burned as a fossil fuel, resulting in a level of decimation similar to the decimation of old growth forests on this continent. As with coir, different places and different scales mean a different answer to the question of sustainability.

This isn’t a pass to blithely consume all of the peat we want here in central and eastern Canada though. There is still an ecological cost, in the form of ecosystem disruption, reduced water holding capacity and carbon emissions associated with the extraction and transportation.

When it comes to peat, in this area, I think that the shift that is needed is more one of consuming less, rather than shifting our current consumption to another ecosystem.

There is one other, often overlooked, organic matter rich system that we can draw from though. One that is actually filled with so much organic matter that it has to be disposed of to prevent unhealthy forms of decomposition.

Urban systems.

Food waste, including material from food production (husks, pulp, cores, cobs etc.), wood from urban forestry and sawdust from lumber processing together can become an exceptionally good growing medium when composted with care and allowed to mature. Unfortunately, there isn’t, (yet) urban composting going on at a sufficient scale and quality that the result is appropriate for use as a growing media. There are some business and organizations working on this though, and I definitely encourage composting at home when at all possible. -And I do mean at all possible, if you have room for a garden, you have room for at least some composting.

See part 2 for what I do (both for potting soil and composting)