Part 2 of: The Growing Media Dilemma

Part 2 of: The Growing Media Dilemma

Friday, January 27, 2023

What I use as potting media for starting seedlings

Also see Part 1: The Growing Media Dilemma

For me, the answer of what to do about the issues around harvesting peat is a combination of minimizing and composting.

For the seeding stage, I still use a peat-based media, specifically Pro-Mix PG Organik Plug and Germination. This is because I seed very densely and some of the pots will spend the first few weeks of their growing lives indoors, which makes them more vulnerable to fungal infections.  I go through around one 107 litre bale for sowing and potting up the tiniest of transplants each year, around 15,000 seedlings in total. For the (very slightly) larger transplants, I use a blend of Pro-mix MP (multi-purpose) Organik and as much finished compost as I can make at home over the course of a year.

To minimize the total amount of material needed, I send seedlings off to their permanent homes at a very young age and a very small size. 128 to 200 plants fit in a standard 1020 flat. When packed up for pickups, I’ve fit up to 100 seedlings in a typical clementine box. Lots of native plants, very little potting soil.

100 native seedlings in a clementine box

For the compost portion, I mix my kitchen scraps, which spend 2 weeks in a Bokashi bucket, with dry, high carbon materials like the bags of leaves I gather in the fall from homes that haven’t (yet) adopted a leave-the-leaves approach to garden care and/or shredded paper and sawdust or wood shavings, which can often be sourced for free from workshops around the city, together in my tumbling composter. Each side of the dual sided composter will hold 2 buckets of kitchen scraps and two to three buckets of dry material. I add a fresh bucket every 7 to 14 days, depending on how fast the kitchen scraps accumulate.

A bokashi pail, some coarse, mostly dry material and bokashi bran

Adding on a 14 day schedule this works out to:

Day 1: Add a bucket each of bokashi and sawdust to side 1

Day 15: Add another bucket each of bokashi and sawdust to side 1

Day 29: add a bucket each of bokashi and sawdust to side 2

Say 43: add another bucket each of bokashi and sawdust to side 2

Day 57: empty side one and start the cycle over again on that side, emptying and restarting side 2 on day 85

The compost comes out about 2/3 done and a bit less than half of the volume that it went in.

The compost as it comes out of the tumbler

I pack it into containers, usually used black plastic tree or shrub pots, top them with some more sawdust and stack them under the bench I my tiny greenhouse, where it matures, shifting from bacterial dominance to fungal dominance until I need it the following spring. Come spring, they get screened and the really hard chunks (mostly stone fruit pits) go on the garden, the medium bits get tossed back into the tumbling composter for a second round and the rest gets mixed with the Promix.

The finished compost, screened through 1/2" wire mesh

I can compost this way for about 150 days per year, which results in about 10 5-gallon pails of compost. The bokashi compost that collects in the early spring and late fall gets buried directly into the vegetable gardens in the areas allocated for that year’s heavy feeding crops. The bokashi that accumulates from when the ground freezes in the fall until it thaws in the spring is put into 5-gallon pails (or any other container I can scrounge) and stored (frozen) in the shed before either being moved to a layered compost bin, if I have enough dry, high carbon material available, or buried in the vegetable gardens, as soon as the spring thaw hits.

In a further effort to further reduce peat use in the coming year, I’ll be looking for re-usable sources of growing media that can be blended with the compost for the growing out stage, when the plants will be outdoors and issues around pests or diseases are somewhat mitigated by the presence of all the life that likes to eat the things that eat the plants. One source that I’ll definitely be exploring is microgreens producers, where fungi and bacteria management for safe food growth in high density, high moisture, settings often necessitate single use of growing media but that same media would be perfectly fine for perennial seedlings in an outdoor growing setting.

When we use a raw material, we are extracting it from somewhere, shifting from one material to another, like shifting from peat to coir, can sometimes lead to a reduction in harms, but it is really important to consider whether it is a true reduction or just a relocation of the most visible harms. Shifting the harms out of sight often means that we lose any say about them or opportunity to effectively mitigate them.

When making decisions about materials, I try to stay close to home. Moving from extraction of local systems to extraction from distant systems is almost never a sustainable solution. I also try to adapt what I do to reflect to local availability and capacity and to cycle resources as many times within a local system as possible to minimize both waste and the need for more extraction.

I try to keep in mind that there is a space between taking too much and taking nothing at all. Most healthy perennial ecosystems have some abundance that they can share. The problems happen when we take more than the abundance on offer, extracting the capital rather than just the interest, and reduce their capacity to meet even their own needs, much less continue to offer abundance for others.

I also try to avoid scaling up to beyond what local systems can sustain. I only have so much compost each year, only so much time to gather bags of leaves in the fall, only so much space to store compost as it matures. Sustainability means not growing what I do so fast or so big that unsustainable extraction becomes unavoidable. Allowing capacity (my own and the local ecosystem’s) to define the limits to growth.