Heidi Hoff

Quartz milkweed jackets

Clearly there is an art and a science to using wood chips that goes far beyond "wood chips = good." In our case, the human health effects of a pile gone hot are bad enough to avoid repeating the experience. In the past, we had inadvertently done as Eric describes: used the chips promptly or let the pile go for over a year without messing with it. The chips in the neglected pile were used for paths (over cardboard), and the spot where the chips were piled was turned into a garden.

As I had not really planned on that compacted clay spot becoming a garden, I did not do much to it. I just broadforked it, spread the remaining wood chips, and broadcast peas all over it, then seeded some squash and corn. I'm guessing that you already know the results: the peas were fine, the corn and squash are pretty miserable. Between the clay, the damage done by "toxic" wood chips and other disadvantages of the spot (shade, proximity to the road and road salt), it will take a lot of reconditioning (and better planning of what I plant there) to make that spot productive. First step will be to sheet mulch it with everything that is currently growing there, other organic matter and, yes, a layer of wood chips.

I don't have a rocket stove or mass heater yet, but I have already changed my management strategies for woody plants on our little acre and a half. In particular, we have chokecherries (Prunus virginiana) in profusion, and anyone who has them will understand that these pioneers like to break new ground every year. This makes them a pain in the backside for people who want their shrubs to know their place, but they are a godsend for easy production of burnable biomass. So I have let them grow densely around the zone 4-5 parts of the yard.

Of course, these shrubby trees serve other purposes. I sometimes harvest the cherries for preserves, but mostly we just let the birds enjoy them. They also provide shelter for nesting birds and those who come here to feed in our gardens. There are a fair number of hawks and kestrels around, so having good cover is helpful. Fallen and rotting wood goes into hugelkultur mounds. If I had a shredder, I would use them for wood chips. And if I start coppicing them actively, I'll have some good material for wattle panels or other basketry.

Yep, my husband learned that the hard way, Gilbert. He's got a touch of asthma anyway, so he ended up with bronchitis-like symptoms, with a bit of a fever, for about four days. I made him wear a mask the next time, but he did not keep it on the whole time he was working with that pile. Another three or four days of misery. Now I do the wood chip work, with a mask. No problems.

For anyone who comes across this later, here's an early reference on an incident investigation: organic dust toxic syndrome

Thanks for all the timely warnings, Eric. We had learned (the hard way) that those hot wood chips were toxic for us, but I didn't count on them being toxic for plants as well. To be clear, we had originally simply "closed" our new raised compost beds with a layer of these wood chips, with the intention of having the wood chips serve as protective layer over the fall and winter months, letting the microbial activity seep into the bed over the next few months. It was only after we had all the beds covered in this way that we learned that we could use the material from the garden center. At that point, the beds had all sat for one to three weeks with their wood-chip covering. We then added several inches of the greenhouse waste and gave the beds a light mixing with a pitchfork (mixing in place, not turning the piles). And now we are in the process of covering them once again with a thin layer of wood chips. We are using fresher chips now, that are not fermenting at all.

In light of the information you provided, I hope we did not go too wrong with all this. We do water our compost beds during and after establishment. We water now and then if we have an extended dry spell, but in our cool coastal region in Quebec, we typically get a good rain once or twice a week. Right now, we're getting a deep soaking rain that is more than we need, but the piles will all be thoroughly wetted. They are perpendicular to a slope, so they catch some water from uphill, but they also easily drain the excess downhill. Also, almost all the beds contain a fair amount of quite rough, freshly scythed plant material (green and dry stems), specifically to provide plenty of air channels.

I guess we'll find out how much luck we have in the spring! I may sow some clover on the piles this weekend, if you think that would be a good strategy this late in the season (first frost is in about a month, 6 weeks).

Wow! Thanks, Eric, for the short course in building soil on rock! I'm already applying many of those techniques and principles, but I'll be bolder in the future. I had really never considered visiting the local cemeteries...

I do share Gilbert's concern about persistent pesticides, but the owner assured me that they use only spot treatments, and the ratio of potting mix to plant matter indicates that very few pots with larger plants have been tossed on the pile.

So I'm going to assume that any pesticides are quite diluted by the uncontaminated materials in their pile. Also, most of the pile has been there for several seasons already and is completely unprotected from the elements, so the effects of time, rain, snow-melt, sunshine and some minimal microbial activity should have further diluted any pesticide residues. And then, in our compost/lasagna/sheet mulch beds, we have so much other organic material that any residue will be even further diluted. We add wood chips to all the beds, using chips that have smoking hot  fungal/bacterial activity going (literally, we have to wear dust masks to avoid toxic organic dust syndrome!!).

So, all things considered, I think we'll soon reduce the garden center's pile significantly. We've already picked up three trailer loads. The owner is delighted to see the pile shrinking and we're delighted to see our garden beds growing!

Thanks so much for the voice of experience, Abbey! I am feeling reassured.

We went and got a second trailer-load today, so we will be incorporating it into several new compost pile / raised beds. None of them will be used until June next year. Fingers crossed!

Just to repeat my main concern: will the fertilizers impede the multiplication of the soil organisms that break down organic matter into plant-usable form?

Thanks!

Thanks for the advice, John. I had not thought of doing a germination test next spring, but that sounds brilliant. I do use spring-seeded cover crops sometimes, so I will do that on these beds.

We are veteran leaf collectors! We even rake neighbors' yards, load them in our trailer and bring home the gold! We're in a small rural community, but people have very urban notions of yard management!

Here's the basic question: Am I asking for trouble by incorporating used potting mix from a commercial greenhouse in our lasagna garden beds? Or is this a true gift?

The owner of the local garden center has given us permission to use as much as we want from their waste pile. The pile is not really compost, just an accumulation of potting soil and discarded plants that for some reason were not salable. Naturally, they do not use herbicides, but they do occasionally use pesticides as spot treatments. And they use liquid chemical fertilizers as well as starter fertilizers in their mixes.

Knowing all that, I would still like to recover this resource. On our site, we have very, very little soil over slate and shale, so virtually all our gardens have to be raised beds. We build them from whatever organic material we can get our hands on -- from scythed weedy growth to horse manure -- combined with what little soil we have and some that we brought in a few years ago (very sandy loam). We make big lasagna beds, mix them or turn them once or twice, let them sit for a season and then start using them.

My concern is that the residual chemicals in the used potting mix may undermine the development of the soil life so necessary to turning our heaps of organic matter into healthy soil.

What do you all think?