Gardening with Pat Munts: Conifers show impact of drought

In late September, a friend and I hiked up to the Big Rocks area on Tower Mountain by way of the Iler Creek drainage. The view of the Palouse was amazing, but I noticed something else as we walked through the forest and along the old burn scar left from the 1991 firestorm. There were a lot of conifers whose needles had turned brown or the trees had completely died; victims of the drought and insect damage.

It’s happening across the region. The prolonged dry weather taxed many trees’ ability to draw water from the soil and that in turn put them under stress which brought, and will continue to bring, insect attacks, particularly bark beetle.

Normally when there is a long period of dry weather, trees adapt by dropping leaves, needles and small branches that are not needed for basic survival. This is one reason the ponderosa pines shed their needles in the fall. We see this in a normal summer when the forest shrubs turn a bit crispy in early September. They are putting themselves into a hiatus until the fall rains return. The record of this shows up in narrower tree ring bands.

In an exceptionally dry year like this one, trees were dropping needles and leaves by early August when we were still a good two months out from the fall rains. I saw a lot of dead 3- to 4-year-old grand fir saplings on our hike as well as dead trees in the middle of a tight clump that couldn’t compete with their neighbors. Besides dropping needles, our native conifers adapt to our seasonal dryness by closing the openings or stoma in their needles to slow their transpiration rates. When it is exceptionally dry for a couple of months like this year, they are then able to draw on an additional 16 to 21 days of water reserves in their roots. When those reserves run out, trees begin dying.

So what can you do at this late date? If the cold weather holds off for a while, water your conifers, especially those that are young or on the edges of your property that may have been missed by sprinklers. Lay a hose on top of the root area and let it run for a couple of days if the weather stays warm. If you are planning to plant a lot of trees for a windbreak or landscaping next spring, plan on laying in a temporary irrigation system or purchasing a 25- to 50-gallon portable water or sprayer tank at a farm supply so you are able to water the trees for a couple of years and beyond. If you have beetle-damaged trees, talk to a forester about removing them to reduce transmission. Both the Spokane Conservation District and WSU Spokane County Extension have foresters who can answer questions and steer you to resources

For questions on forest management, contact forester Garth Davis of the Spokane Conservation District, garth-davis@sccd.org or (509) 535-7274, or regional extension specialist Steve McConnell, smcconnell@ spokanecounty.org or (509) 477-2175.

Pat Munts is co-author, with Susan Mulvihill, of “Northwest Gardener’s Handbook.” She can be reached at pat@inlandnw gardening.com.