Wednesday, September 11, 2019

You have a pile of yard waste. How best to deal with it?

Walking stick, coulda been a bonfire.
So, youʻve got a pile of yard waste or pruned tree limbs. What to do with it?

1. You could use it; 2. You could let it rot (compost); or 3. You could burn it.

This is an argument for the first and the second, but not the third.

Some yard waste, if it doesnʻt have a bunch of weed seeds in it, can be mulch to keep weeds down and retain soil moisture. Or parts of it can be used as planting material (stick a plumeria stalk or a trimmed hibiscus branch in the ground and theyʻll grow). Chunks of wood can be slabbed up for construction projects, or carved into art objects. Really, you donʻt need to buy a walking stick...itʻs called a stick for a reason.

Composting is magical. It turns waste into a valuable soil amendment. And you can get all scientific about it to get the best, fastest results that produce enough heat to kill weed seeds. Or you can just pile the stuff up and the natural world will break it down in its own time. The crawly bugs and fungi and bacteria, the mesophylic and thermophylic organisms, the worms and the larvae, theyʻll do all the work.

What about the burning option? It gets the volume down fast, and creates wood ash, which has a lot of potash and other micronutrients that you could use in your yard.

There are times when burning is appropriate, but the downsides to burning are compelling. The heat sterilizes the soil under the fire and kills anything living in the greenwaste. If composting is a technique that celebrates life, fire is the opposite. Fire can be a natural process, but weʻre not talking about lightning-lit fires in native forests or savannahs.

(We can concede that for some species fire is a friend—grasses in many cases thrive after fires, both because the competition is killed off and because the ash fertilizes the soil. And we note in passing that a dry compost pile can sometimes catch fire, but thatʻs another discussion.)

What else?

Smoke from fires can be irritating to human (and other species) breathing and to eyes. It can make allergies worse. Sometimes toxic compounds that were locked up in the biological matter can be released into the atmosphere.

Wood smoke contains particular matter as well as chemicals in gas form. Breathing that stuff can have both short-term and long-term health impacts.

Hereʻs a paper on hazards of wood burning. And hereʻs a warning from the Centers for Disease Control and Prevention.

And then, of course, thereʻs the elephant in the room—the whole climate thing. Every time you burn, youʻre dumping a pulse of greenhouse gas into the atmosphere. Itʻs why folks are so exercised about the burning of the Amazon forests.

A few boring statistics: For every pound of wood you burn, you create 1.5 to 1.9 pounds of carbon dioxide (depending on the carbon density of the wood). Carbon dioxide, of course, is a big greenhouse gas. You also produce other greenhouse gases, like nitrogen oxides.

So to go back to the start, weʻre all better off if you make something (compost, mulch, a carved elephant, a picture frame) than if you immediately convert your woody waste to greenhouse gas. Youʻre just locking up that carbon for longer.

It seems clear that keeping that carbon in the soil rather than in the atmosphere is a good thing. And itʻs a good thing for more than just the climate, according to a 2005 article by Canadian researcher Henry H.Janzen. 

"Soil organic matter is far more than a potential tank for impounding excess CO2; it is a relentless flow of C atoms, through... myriad...streams—some fast, some slow—wending their way through the ecosystem, driving biotic processes along the way."

© Jan TenBruggencate 2019


Kyle said...

To avoid scaring anyone about composting, it should be noted that compost fires are extremely rare and virtually nonexistent in backyard compost piles, especially in humid Hawai'i.

Anne said...

I was always told to keep weeds out of compost, but maybe that applies more to the colder climates? I'm gonna start adding them now! Thank you!

Jan T said...

Weed seeds can survive a compost pile that doesnʻt heat up sufficiently. So if youʻre not assiduous in managing your compost pile for most efficient composting, for the worst weeds, I might reasonably separate out the seed heads.