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Damage likely from winter's severe cold

KENNEWICK -- It's been at least four years since local gardeners have had to worry much about winter injury on their landscape plants.

However, this past winter's severe cold spells have resulted in some very sad looking plants, such as photinia, winter creeper and rhododendron.

Plants such as photinia are not fully hardy for our area.

Photinia is rated as hardy from USDA Zones 7b to 9, meaning it can withstand temperatures down to 5 degrees. Based on the hardiness zones, damage can be expected to occur if the temperature goes below 5 degrees. It did, proving the limits of plants such as photinia.

That's the problem with using plants that are not fully hardy here.

To be safe, we should only plant trees, shrubs and perennials that are hardy to Zone 6b. When we use plants that are hardy to Zone 7 or higher, we're asking for trouble.

So what can be done for shrubs and trees like photinia? Rip them out? Wait! Actually, it's best to wait for warmer spring weather and give the plants a chance to recover. Wood that looks dead right now, may not be.

Once growth has or hasn't started by late spring, you should start pruning out the dead wood.

How can you be sure a branch is dead? Use your fingernail to scrape away the bark on the twigs or use a pocket knife to make a shallow cut just under the bark of woody branches. If the branch is alive, the tissues beneath the bark should be bright green or white. If it's dead, these tissues will be brownish, shriveled or soggy. If you find dead tissue at the tip of a branch, keep going into older and larger diameter wood until you find healthy live tissue. Twigs and buds at the end of branches are less hardy than the more mature tissues.

When you prune out the dead wood, prune back to live tissue using proper pruning techniques. Even if you end up pruning shrubs all the way to the ground, hope may not be lost. The roots of the shrub may have escaped injury due to insulation from the soil and snow. Before uprooting a shrub like photinia, see if new growth starts to develop at the base of the plant. Be patient.

Injured plants that survive will need some TLC in the coming growing season. Don't stress the plants with too little or too much water. Don't apply any fertilizer if they grew well last year. If planted in or near the lawn, they probably get plenty of nitrogen already from lawn fertilizer. Excessive amounts of nitrogen may stimulate growth that the plant may be too weak to support.

As spring and summer unfold, we'll see the extent of the damage caused by the severe cold this past winter. In addition to damage to roses, rhododendrons, photinia and winter creeper, I anticipate seeing injury on plants that are not hardy in Zones 6a or 6b and maybe even on some plants that should be hardy.

Time will tell, but right now just be patient. Remove only what's obviously dead and then wait for warmer weather to encourage new growth.

* Marianne C. Ophardt is a horticulturist for the Washington State University Extension Office in Benton County. Read more of Ophardt's Garden Tips columns at www.tricityherald.com/ophardt.

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