Smoky air is good for plants, but ash, particulates aren’t

QIn this recent “carbon rich” atmosphere, does that at all benefit plant life? Or do they only absorb the carbon dioxide they need regardless of an enriched environment?

— Gary Miller,

saratoga

AIn theory, the smoky air we’ve been experiencing should be good for plants as it, as you say, provides plants with an ample supply of carbon dioxide, but it’s not that simple.

Plants absorb carbon dioxide from the air and combine it with water and light to make carbohydrates, a process known as photosynthesis. In doing so, they release oxygen back into the atmosphere, for which we are thankful. Some plants react to a family of chemicals in smoke that makes them grow thicker and sturdier stems, and smoke also can cause increased seed germination in some plants.

A side benefit of the smoky skies is that the haze diffuses sunlight, helping to protect plants from getting too much direct sun.

The smoke can be helpful in those regards, but unfortunately, the smoky air also contains large amounts of ash and other particulates, which are not good for the plants. It can coat the leaves and clog the plant’s stomata, which are the tiny pores where the plant absorbs carbon dioxide and releases oxygen. The blockage can suffocate the plant.

Even short-term exposure to smoke, studies have shown, can destroy chlorophyll in plants, reducing photosynthesis by up to 50%. The exposed plants become stressed and weak, and shift into survival mode. Everything then slows down, including fruit ripening. If the exposure goes on for a long time, which it has in the Bay Area, it can seriously harm plants and also affect the taste of your produce.

Gardeners should be looking for wilting or other signs of stress in their plants. Washing them off with the hose can help get rid of the gunk coating the foliage. Now that the skies appear to be clearing, plants that haven’t been severely harmed will resume their normal patterns.

QWe have a huge, beautiful native oak tree in our front yard. We think it’s about 300 years old.

In late February, it begins to sprout buds for new bright green leaves.

Toward the end of summer, leaves turned dull colored and begin to drop, little by little. In October and November, more and more leaves come down, depending on weather and wind. A frost speeds up the drop. By the end of December into January, the tree is bare.

This year in early September, a huge number of leaves began dropping every day. My husband was out there every day cleaning up. Now, there’s only a small sprinkling on the lawn. We have been thinking perhaps it signifies an early winter coming. We’re wondering if the smoke and darkened days had an effect on the tree to make it shed.

The last few days have been sunny, so perhaps it’s reverting to its more normal pattern.

Do you have any idea as to why it has changed its pattern of losing leaves? We have enjoyed this beautiful tree since moving into our home in 1966. We hope it will remain healthy for others to enjoy for many years to come.

A— sharon Johnson, san Jose

Old gardening folklore has it that leaves falling early mean the fall and winter will be mild. Another adage says an abundance of acorns can signal a hard winter. Interesting, but not sciencebased.

Plants, especially trees, react after a weather event, not before, so your grand old oak is likely reacting to conditions now, not predicting a weather pattern in the future.

The most common factor in oak trees shedding their leaves earlier than expected is some type of environmental stress. A prolonged drought, disease or an insect infestation can cause the tree to drop its leaves in an attempt to conserve energy, food and water.

The smoke certainly could have triggered such a response, but you should also check that the tree is getting enough water and that you don’t have an insect problem.

Our recent higher than normal temperatures also might have stressed out the tree.

Now that skies are clearing and lower temperatures are on the way, things should get back to normal, but it might take some time for the tree to get back to its regular schedule.

If you notice the tree going into a decline, you should contact an arborist to examine it. You want to ensure it stays healthy for at least another 300 years.