We gasped and choked our way through the smoky summer, but how did our plants do? Deprived of normal sun exposure, and surrounded with quite an abundance of carbon dioxide, they struggled too. My bean leaves show the stress, looking like someone sandpapered over grained leather, green only in valleys and veins. Thrips are partly to blame, I know, but most other exposed leaves look stressed, too.
My tomatoes didn’t do very well this year either, but I let a lot of volunteer cherry tomatoes and bulbing fennel grow, and those plus sweet potato vines shielded my chile plants from smoky air, allowing those chile plants to produce abundantly. Honeybees aren’t fazed, having a high time in the tomatillos and mint blossoms.
Very little research has been done on the effect of smoke on growing plants. One recent study did find that despite the increased carbon dioxide in the air, photosynthesis was reduced because the stomata (the pores that take in carbon dioxide) conductance and assimilation were lowered. In other words, the smoke can lead to high-vapor pressure that can trigger the closing of those stomata. Reduction in photosynthesis means the plant is not adequately feeding itself. If it lacks nutrients, then the consumer of it lacks nutrients as well.
We don’t know precisely what this reduced photosynthesis does to the nutrients we depend on coming from plants that provide our food, while it’s busy producing junk food or sugars. Plants love the sugars, but we expect more. We do know that the nutrition in our vegetables has declined significantly over the years, and the usual blame is attributed to the depleted soil they’re grown in. Although this is a different nutritional loss than that of wildfire smoke, together they impact us even harder. Agricultural (and home garden) soil has been depleted by synthetic fertilizers and pesticides that destroy some of the soil-dwelling micro-organisms.
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Fertile or healthy soil is a complex system of living things: arthropods, fungi, nematodes, bacteria, protozoa, micro- and macro- creatures such as earthworms, centipedes, millipedes, consuming and assisting decay of organic materials in the soil. They, not our organic fertilizers, are responsible for feeding our plants. Our organic fertilizers help these microbes and mycorrhizae feed minerals and other nutrients to our plants, but synthetic chemical fertilizers will starve them.
What can we do to keep our soil healthy and productive? Crop rotation helps because different crops take up nitrogen in different amounts, and since nitrogen is easily leached from soil, it often needs to be added back in some way. Calcium is crucial for humans and plants and is usually provided to soil from decaying matter and the weathering of rocks, but it and other “minor” nutrients may be leached from soil by acid rain or erosion. Alkaline soils are prone to be deficient in manganese and magnesium. Our soil naturally is deficient in magnesium, the reason why Epsom salt (magnesium sulfate) often helps plant vigor. I use a teaspoon of that dissolved in a pint of water as a foliar spray when chile plant leaves are too light green in color, providing a fast greening.
Organic material such as compost and other mostly decayed matter is the binder that ensures your plants can take up the minerals they need. If matter hasn’t thoroughly decayed, it may rob the area of nitrogen to facilitate decay, and only then yield the borrowed nitrogen and add more. Using organic mulch materials is not regarded as reducing nitrogen supply, since it’s only on the soil’s surface, not in the root zone. Compost improves the structure of soil and its water-retention capability and adds nutrients to this wonderful and complex skin of our planet.
Treasure those leaves that fall from your deciduous trees, and scatter old needles cast off by evergreens rather than bunching them up. Experts say needled evergreens won’t change the pH of your soil when laid atop, but I wouldn’t take a chance on it. If the pH is off, plants just struggle. A little more acid on our soil, say in the form of gypsum, may be helpful since our soil is so alkaline, but too much acid will result in favorable conditions for blueberries and not much else.
If the summer’s smoke reduced harvest in my yard, I didn’t notice, for I’ve been scrambling all summer to keep up with the production, canning, freezing and dehydrating.
Send garden questions to firstname.lastname@example.org or Gardening, Idaho Statesman, P.O. Box 40, Boise, ID 83707.