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The Garden Plot for August 10, 2007
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: “Smoke and Gardens”
We know how the smoke in the air is effecting us, but what effect does it have on our garden and landscape plants?
Fortunately, plants don’t breathe as we do, so they don’t have to worry about bad air quality and particulate matter. In fact, particulate matter in the air is organic carbon molecules, or burned up plant material. So it is remotely possible that particulate matter could wind up falling into our gardens and increasing soil carbon.
That benefit may be a bit far-fetched, but as it turns out, smoke may be a good thing for Western Montana garden and landscape plants. July and August in Montana are usually full of sun and intense, bright light. The light levels are so high that our plants often suffer sunscald, the plant version of first degree sunburn. Smoke in the air attenuates and diffuses light. This attenuation reduces the intensity of direct sunlight. Reduced sunlight in August can diminish the incidence of sunscald injury on fruit and on the trunks of young trees and shrubs.
Reduced sunlight may also help plants in another way. It might decrease transpiration rates, the rate at which plants loose water to the atmosphere. In other words, the smoke may be acting a bit like a shade cloth. Plants are always engaged in a balancing act. Normal growth requires that plants balance transpiration with photosynthesis (making food from organic carbon, water, and sunlight) and with respiration (burning food up for basic maintenance and growth). Lower light levels and lower transpiration rates mean that plants can keep open the tiny pores in their leaves through which carbon dioxide enters. When it is sunny and dry, plants close these pores (called stomata) and then can’t take in the carbon dioxide they need to make food during photosynthesis. So, decreased light intensity may actually help plants store more carbon as fruit and root tissue. Tree fruits, such as apples, are the most likely to benefit from reduced light intensity.
This may be an important benefit because many Western Montana trees and shrubs suffered in July when it was abnormally hot and relentlessly sunny. Transpiration and respiration was increased beyond what photosynthesis could compensate for. Hence plants burned up more food than they made and started to show signs of stress.
The best thing we can do to help our plants now is to keep them well watered. Lawns need about 1 inch of irrigation water per week, spread out over 3 to 4 watering times. Non-native trees and shrubs need approximately 2 inches of irrigation, in one deep soak per week.
So, though the smoke is a bad thing for us, don’t worry about smoke injuring plant growth. In fact, considering the unusual heat this year, it may actually be helping.
Helen Atthowe's new short program of gardening tips
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