When you see something going on with your trees, sometimes it’s because of what happened years ago.
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“Trees live in the long term,” said Sharon Yiesla, plant knowledge specialist at the Plant Clinic of The Morton Arboretum in Lisle. “They have slow reaction times and slow life cycles. When you care for trees, it helps to think that way too.”
Every fall, for example, evergreen trees and shrubs, such as pines and spruce, drop their oldest needles. A white pine will discard its two- or three-year-old needles; a red pine will drop four-year-old needles.
Sometimes it just seems like an awful lot of needles. The reason may be that two or three years ago, your white pine got lucky. “Maybe there was a lot of rain that spring and the plant was able to grow a bumper crop of new leaves,” she said. “Now their time has come, and they’re all falling at once.”
As long as the tree is only dropping its oldest needles — the ones growing closest to the trunk — that’s just the way a white pine grows, and it’s nothing to worry about.
Things that happened years ago can also mean real trouble. For example, the effects of a bad drought can take years to kill a tree.
When the soil stays too dry for too long, the small, fine feeder roots that make up much of a tree’s root system dry out and die. That can mean that even when it starts raining again, the tree doesn’t have enough roots to absorb or store as much water as it needs. Over time, that water deficit means the tree struggles to support its leaves and branches. The stress accumulates until the tree dies.
Ironically, too much water can have the same effect. “When a tree stands underwater in a flood or has to live in waterlogged soil, roots often rot,” Yiesla said. Roots that die from rot, like those that die from drought, can leave the tree without enough of a root system to support itself in the long term.
Soil compaction from construction work is another slow-moving tree killer. A tree can die because the soil in which its roots have to live was packed down by heavy equipment traffic or by piles of building materials or debris.
“By the time the tree finally dies, you may have been enjoying the new patio or kitchen addition for years,” she said. But all through those years, the tree was gasping for air and water that couldn’t penetrate the compacted soil.
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That’s why, when faced with a tree problem, the Plant Clinic will often ask about the history of the yard. It’s also why smart gardeners think about the long-term effect of big changes on the property, and they often keep a few notes.
“Having some sort of a record of what has gone on in your yard and your neighborhood can be a big help in diagnosing plant problems,” Yiesla said. “The end of the growing season is a good time to recall the major weather events and other big changes this year, and jot them down for future reference.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or [email protected]). Beth Botts is a staff writer at the Arboretum.