Heat-dome impacts on landscape foliage in the Woodinville area

Tom Quigley, a certified arborist, often consults with property owners on tree-risk and preservation issues. Courtesy photo

By Tom Quigley

The heat dome that covered the Puget Sound region in late June of this year left a wake of scorched and burnt foliage on trees and shrubs and caused property owners to gasp in horror.

Many have asked how that happened and what can be done about it.

It may seem obvious that the sun was too hot for the foliage, but there is more at play here.

Cumulative stress in trees and shrubs is well documented in the Puget Sound region. Just a couple of hot summer days can cause a tree or shrub to transpire excessive moisture from the leaves and needles, leaving it more stressed than the previous year. These stresses add up over time and the results can be devastating.

While the foliage is definitely fried, the small twigs may be capable of producing new leaf buds. The same is true for both evergreen and deciduous trees and shrubs. Your tree or shrub will naturally drop the burnt foliage as it grows new foliage, but this may take a season or two. Resist pruning the tips of your shrubs and trees as a way to remove the unsightly damage.

Pruning multiple twigs to remove scorched foliage will result in the tree or shrub using stored energy to replace the twigs and small trimmed branches. If the affected shrub is ‘sheared’ to remove the damaged foliage, it will need to produce more response growth than if it is left to recover more slowly.

Removing scorched leaves one at a time can be a labor of love, but the results are satisfying. What our trees need is additional hydration. They grow larger every year, which requires more water and soil nutrients, but they typically receive less of these vital resources each year.

A tree or shrub produces some of its needed nutrients from the debris that it drops seasonally. When we remove the shedding needles and leaves from the ground around our trees and shrubs, we release a natural source of organic nutrients. That is why we must add mulch to our garden beds and around our trees. Good organic mulch helps build healthy soil, helps retain moisture, helps moderate soil temperature both summer and winter and helps retard weed growth.

Our gutters and downspouts can be a simple source of enough water to make a huge difference. There are a host of ways to capture and use rainwater to your landscape’s advantage. Rain catchment barrels, underground tanks, designed rain gardens, and sheet flow are a few of the common ways to provide your trees and shrubs with the extra hydration they need. There are lots of great websites that discuss rain catchment and use.

Tom Quigley has been an ISA (International Society of Arboriculture) certified arborist since 1996. He consults with property owners about tree risk issues and provides tree preservation plans for construction permitting, both residential and commercial.

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