Smoke, Ash, Dust & Plant Health
This weekend, my band played maritime music at the venerable Wooden Boat Festival in Port Townsend, Washington. We were hoping that the breezy seaside location would mean less smoky air than we’ve been experiencing at home, and to some extent it did. Even so, I found myself coughing funky gunge for hours afterwards, not too surprising when you learn that Seattle had the worst air quality on the planet that day. We’ve held that dubious honor before, since regional winds all too often carry smoke and even ash from far too many wildfires. When the West burns, even coastal areas can get the fallout.
Harmful as smoky air is for people, it can have some surprisingly positive effects on plants and even soil. While most research has looked at the damage smoke can do to plants, a few studies have noted additional beneficial results. After the 1980 eruption of Mount St. Helens, it was noticed that while plants died in badly hit areas, where ash was distributed less deeply, apple and wheat crops were increased by about 25%, an effect that persisted for some years. Researchers also noted that thinner coats of ash and even ashy crusts actively help dry soils retain more water and add minerals and other nutrients to the soils. That said, it’s still true that when particulate counts are high, the little bitty bits can cling to foliage, clogging up the little window-like structures (stoma) on foliage that allow plants and air to freely exchange water and oxygen. Dust and debris can similarly reduce free gas and water exchange, so it’s still important to hose down plants during and after smoky periods.
New News Is Good News
Even so, it has long been assumed that the net result of extended smoke exposure was as bad for plants as for people and critters. A report in the January 2020 Journal of Geophysical Research: Biogeosciences confirmed that wildfire smoke may actually increase plant productivity. During the summer of 2018, researchers tracked the ecological effects of wildfire smoke in California’s Central Valley and correlated their findings with a number of other recent smoke studies. It turned out that smoke generally only blocks about 4% of sunlight (less than previously supposed), and that the way smoke diffuses sunlight lets light penetrate more deeply into dense tree canopies, increasing the photosynthesis efficiency of canopy foliage and increasing overall plant productivity.
What’s more, in some situations, the scattered light of smoky conditions measurably improved plant health and productivity in restored wetlands and natural bog environments. Who knew? There are very complicated biochemical reasons for all this, but it seems likely that, given the frequency of naturally caused fires and volcanic activities over the millennia, many plants have adapted to take whatever advantage may be possible from the resulting conditions. So what about our gardens? There, too, we may find more resiliency than expected, especially if we stay vigilant abut watering on hot, smoky days, as plants with dry roots are susceptible to more damage of all kinds than well watered ones.
An Unexpected Benefit Of Dust
This has been a good year for Cabbage White butterflies and thus a tough year for cabbage, kale and other greens. After a frustrating spring, I was delighted to notice that the Cabbage Whites had retreated from my Pea Patch garden bed, even though they were still very active in my tiny home garden. The difference was that the Pea Patch community garden abuts an active construction site where a wonderful playground is being built, relying heavily on natural materials. Many yards of soil, wood chips and gravel have been dumped and moved about all summer, causing clouds of dust to settle on nearby beds. As it turns out, mine is one of the lucky ones, as the heavily dusted kale in mine soon produced new, unblemished and un-nibbled foliage.
Where neighboring gardeners were regularly hosing off foliage, the caterpillar damage continued unabated. Since my Pea Patch garden is largely a pollinator patch and doesn’t need frequent watering, I’ve largely let it be for the bees (if not to everyone’s delight). Apparently, that dusty coat on my kale caused any Cabbage White eggs to be smothered and the adults must have grown discouraged, which is fine by me. Now, as I’m planting fresh kale and greens, broccoli and Brussels sprouts, I’m experimenting with deliberately dusting the young foliage on some of the plants. It will be interesting to see if dirtying the leaves helps keep them clean of caterpillar damage! Onward, right?