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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

Gardening: Heat waves wreak havoc on plant metabolism

These Alberta spruces show heat damage on their southern sides. They were sitting near a concrete curb in a landscape that probably wasn’t getting enough water. We will have to wait until spring to see if they recover.  (Pat Munts/For The Spokesman-Review)
By Pat Munts For The Spokesman-Review

The heat is gone for the summer, but it left many gardens in shambles. Many conifers were scorched on their south and western sides, deciduous shrubs lost leaves, berry crops dried on the canes, tomatoes and squash didn’t set fruit and fruit trees dropped fruit. So, what can we do in what’s left of the growing season to help our plants?

There are several reasons for the damage:

• Many plants were already under stress from the lack of rain in the spring. Most of us hadn’t cranked up our irrigation systems for hot weather so the plants didn’t have reserves available.

• As plants mature into summer, they gain more heat tolerance. However, a heat wave came before the plants had a chance to toughen up, so the still-tender spring leaves basically cooked.

• We had three to four days of temperatures over 100 degrees with nights only down into the mid-80s. The plants could take a single hot day but not a string of them. Plants shut down transpiration and couldn’t pull up more water. As a result, the leaves just dried out.

Fir and spruce trees seemed to be hit particularly hard. I have seen a number of fir trees around the area with rusty red needles on their south or western sides.

Dwarf Albert spruces all over town are showing burnt needles on their exposed flanks. I completely lost an Alberta spruce that was transplanted this spring. Are the trees going to be able to replace the needles next spring?

This was such an extraordinary event we are going to have to wait and see. Most conifers grow from the tips of their branches and don’t replace needles farther back on a branch. So, unless the tree is completely dead, just leave it until spring and see what happens.

Deciduous shrubs lost a lot of leaves especially in areas exposed to the sun. If just the leaf tips or areas directly exposed to the sun are crispy, the plant will likely come back next spring. You might have to do a little pruning to remove dead twigs, but it would be worth the wait to see what happens in the spring.

When our native plants in the wild get hit with dryness and heat, they often just go dormant early and wait until next spring.

Leave dead leaves on a plant to provide shade for other leaves and prevent more damage.

Now that it has cooled down, our vegetable crops should rebound.

Peppers, eggplant, tomatoes and squash will start setting fruit again. Corn seemed to ripen earlier so watch your late corn, so you don’t miss its peak. Peppers will likely be smaller this year, but they grew so early, they might have enough time to actually turn red. Apples and pears look like they may be ripening a little early so keep an eye on them.

Keep watering all your plants deeply so they can go into fall well hydrated. It will help them recover.


Pat Munts can be reached at