Monday, October 3, 2011

Serial Killers in Your Landscape

Extreme weather has hammered landscapes around the country—and around the world—this year. Depending on where you live, if your trees and shrubs weren't being parched by record-smashing heatwaves and exception drought conditions, they were being waterlogged or iced over. Throw in destructive high winds, hailstorms,  tornadoes, and...well, you get the picture.

National Oceanic & Atmospheric Administration/
Department of Commerce
Even if your major landscape plants made it through the growing season, they probably didn't do so unscathed. Trees and shrubs subjected to serious drought and long-term flooding nearly always incur some degree of root loss. Or perhaps they lost limbs, or were defoliated, by other extreme-weather events.

Whatever "ill winds" your valuable landscape plants have suffered, they are now in mortal danger of succumbing to subsequent "serial" assaults while still in their weakened condition.

Roots take time to regenerate. Wounds from lost limbs or other injuries take time to callus over. This recuperative period can last up to five years, during which a plant pours all the energy it can into recovering from its injuries. If it hasn't had time to restore itself before being hit by one or more additional extreme-weather events, this year's injuries could result in its death this winter, next year or even several years later.

[Note: Weatherproofing Your Landscape: A Homeowner's Guide to Protecting and Rescuing Your Plants, provides guidelines on repairing damage, as well as how to manage long-term post-damage care.]

National Oceanic & Atmospheric Administration/
Department of Commerce
 I have trees that were severely damaged by a catastrophic ice storm in 2007. They've been in particular danger this past year during our record-setting heatwave and exceptional drought. So has a big oak tree that lost a substantial part of its root system during a construction project a year of so ago. For years to come, I'm going to be on pins and needles each spring, waiting to see if these specimens have the energy to leaf out.

But there are things you can do to help make sure your stressed landscape specimens have the best possible chance to recover. (And whatever measures you take now could save you the work and expense of replacing dead specimens later.)

Where serious root loss is concerned: our big root-damaged oak was treated with a growth retardant that reduced its top growth while its roots regenerate. [See the Surviving Dead Roots posting—9/9/11.] This might help your drought or flood-stressed tree as well. (Consult a certified arborist.)

Deep-soaking the root system is essential in drought-stricken landscapes. Last month, I dug a hole in a frequently watered border bed, to plant a new shrub. The drought was so extreme that, once I got down about a foot, the moist soil turned brick-dry. So in extreme, prolonged droughts, even digging down several inches to check soil moisture doesn't always tell you what's going on deeper still. I've found that deep soaking with a drip hose...then deep soaking again a few days later while the soil is still moist...gets moisture down to the deepest feeder roots (which can be up to 20 inches below the surface).

Deep-soaking stressed specimens now and throughout winter (when the ground isn't frozen) is essential. Soil moisture helps insulate plants against winter cold.

If too much water is the chronic problem, you might want to consult a landscape architect to advise you on how to improve drainage without doing more damage than good. For instance, raising the soil level around plants, or trenching French drains within their critical root zones, are major no-nos!

So keep in mind that a stressed plant is highly vulnerable to future stressors that occur before it has had time to recover. Do not fertilize stressed trees during their recuperative period. And check with an arborist or your cooperative extension agent if you feel that your specimen might be diseased or infested. (Stressed plants are magnets for bugs and diseases.)

We're curious: What kinds of special problems have extreme-weather events caused for your landscape plants?

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