Filbert blight; crimes against rhodies
Garden writer Ciscoe Morris discusses symptoms and prevention of Eastern filbert blight, and details the surprisingly tricky ins and outs of growing that Northwest favorite, the Rhododendron.
Special to The Seattle Times
Kubota Garden Fall plant sale: 9 a.m.-noon, Sept. 7. Experts on hand to help with selection. Renton Avenue South and 55th Avenue South, Seattle (www.kubota.org).
Seattle Tilth Harvest Fair: 10 a.m. to 4 p.m. Sept. 7. Hands-on community festival with workshops, cooking demonstrations and activities for all ages. Meridian Park, 4649 Sunnyside Ave., Seattle (www.seattletilth.org).
Heronswood Open Garden & Plant Sale: 10 a.m.-5 p.m. Sept. 7. Tour, shop and learn from visiting experts at the Kingston garden. Sale and lectures are free, $10 donation requested to tour the gardens (www.heronswood.com).
In the Garden
Harry Lauder’s Walking Stick (Corylus avellana ‘Contorta’) is an ornamental filbert grown for its twisted, gnarly stems. Unfortunately, a devastating fungus disease has moved into our area that can cause extensive damage and even kill these highly popular shrubs.
Eastern filbert blight causes cracked, sunken cankers that interfere with food and water transfer, resulting in death of the branch beyond the point of infection. Spores of the fungus are spread by wind and once in the tree, are splashed by water to neighboring branches. If cankers are not pruned quickly, they will continue to spread throughout the tree until they reach the main trunk.
Once the trunk is infected, the blight usually kills the tree. Control is difficult. Fungicidal sprays are only effective if applied every week through the growing season. The only hope is to prune off branches with cankers at the first sign of discolored wood. Inspect your plant in spring for the first sign of cankers in spring.
It’s difficult to spot early infections, and if you miss them, branch dieback will continue at a rapid rate. Once the infection spreads, it’s likely that you won’t be able to save your plant.
Rhododendrons are among the most popular plants in the Pacific Northwest. Most of us cherish them for their exquisite flowers that come in every size and shape imaginable, while collectors covet the ones with exotic fuzzy leaves and/or spectacular peeling bark.
Despite their popularity, rhodies are not the easiest plants to grow, and many die, especially in the first few years after planting. Worst of all, the way we care for them often leads to their demise.
According to experts with the American Rhododendron Society, overwatering is the No. 1 killer of rhodies. This is especially true when they are planted in poorly drained soil. In clay-soil conditions, bring in topsoil and plant the shrub on a mound of soil that will drain well. The roots require plenty of air and will rot if they are constantly sitting in water.
Paradoxically, the second most common cause of rhody death is underwatering. Rhodies have extremely shallow roots, and in well-drained soil, the plant will die of thirst without adequate moisture near the soil surface.
Rhodies typically need watering once per week in dry weather. Covering the roots with a light, fluffy mulch, such as compost or wood chips, will help slow evaporation. Another way we do in our rhodies is by overfeeding them, particularly with synthetic fertilizers. These contain salts that can build up and harm the roots. Apply organic Rhododendron food once per year, in early April.
Planting too deep is another way we put the “el kabotski” on our rhodies because of the shallow root system. If you planteven a quarter-inch deeper than it came out of the pot, the roots suffocate.
Avoid mulching with beauty bark as it tends to become too packed. Finally, even if you do everything right, sometimes rhodies die anyway. I’ve noticed it’s always the rarest, most expensive one, and I’m fairly sure it croaks just to be ornery!
Ciscoe Morris: firstname.lastname@example.org “Gardening With Ciscoe” airs at 10 a.m. Saturdays on KING 5.
About Ciscoe Morris
Ciscoe Morris' column runs Thursdays. His show "Gardening with Ciscoe" airs at 10 a.m. on Saturdays on King 5.