|
|
  |
|---|
How can they be maintained so that the leaf looks healthy and attractive for the eleven months when the plants aren't blooming?
Check nurseries and garden centers for rhododendrons that enhance landscapes throughout the seasons. Select a likable leaf! Many rhododendrons have stunning leaves. Those in the yakushimanum group have attractive whitish-tan felting underneath the leaf, which shows up when the leaf is turned over. This under-leaf surface, called "indumentum" appears on many other rhododendrons, also. One called R. 'Sir Charles Lemon' has deep brown lower leaf color, giving the plant great beauty in fall landscapes Others have attractive leaf forms, such as the clear ovals on R. 'Bowbells.'
Considering leaves may also lead to thoughts of a frequent garden problem, chewed edges on rhododendrons. The most common cause of this is the root weevil, present in several different species in western Washington.
Root weevil adults chomp on and cut small irregular notches from the edges of leaves. Chewed leaves remain on the plant for years. Root weevil pests avoid some rhododendrons. Research done at Washington State University, Puyallup, discovered many garden rhododendrons that don't seem to be chewed or are seldom chewed. Some which show good resistance to weevil chomping are 'P.J.M.' (pink), Dora Amateis (white), and any of the Yakushimanum types. (pinks and whites.) Yellows 'Crest' and "Odee Wright' also resist damage, as does a pink with large trusses of spectacular blooms, 'Point Defiance. ' The entire list studied by WSU is available in a bulletin, EB 1229 "Rhododendron Problems." You can order this bulletin by calling your local WSU Extension office during business hours (Snohomish County, 425-338-2400; King County 206-296-3900, and Pierce County 253-798-7180.) or order on line from WSU Publications.
Why would an insect eat one plant and ignore another? Some leaves contain chemicals that repel the insects by tasting bad. 'Oceanlake,' a common blue rhododendron, has these. Other plants have leaf shapes that resist being bitten because they fold into thickness that the insect jaws can't span. Check with your nursery for resistant cultivars.
Azaleas and rhododendrons are in the same botanical family, and require similar growing conditions. Most of them do best in filtered light such as that under open deciduous trees. But they do require light for best bloom and will not set buds well if the area is too dark. Morning sun in an east-facing situation. Protect them from hot, exposed western or southwestern locations without tree canopy or other shade, although some will thrive in sun if they receive enough water.
Both rhododendrons and azaleas need moist, well-drained acid soil (pH 4.5 to 6.0). In general the soil acidity isn't a problem, since our native soils tend to be within the desirable acidity range. Rhododendrons will not thrive well in soils that have been heavily limed, or in areas where masonry rubble and slurry from concrete mixing might have been dumped into the ground. If construction has recently been completed, check for such conditions before planting.
"Moist soils" mean those that have been amended with organic materials so that they will retain water, but won't leave water puddles or sogginess standing around the roots of the plants. If the native soils are clay, hardpan, or severely rocky consider planting in an amended raised bed. Add amendments such as compost to the entire planting bed, not just to the immediate hole where the new plant will go in. You don't want to create a planting hole that differs radically in texture from the surrounding soil.
Sometimes rhododendrons and azaleas fail to thrive because they have been planted too deep in the ground. When planting, after amending the soil, let the ground settle a bit and then place the plant with the root ball just slightly ABOVE the surface of the ground. ("Slightly" means less than 1/2 inch.) These plants have very fine, fibrous roots on the surface of the ground, and they need oxygen to thrive.
Occasionally, moving and resetting the depth of a rhododendron, to bring the root ball closer to the surface, can improve its bloom if bloom has been scarce.
Place soaker hoses around the plants, or use an adequate irrigation system. Newly set plants of all types need water during their first two to three years while they are becoming established.
To conserve water and reduce weeds, use a mulch. Cover the ground around and over the roots with 2 inches, or less, of a coarse organic mulch (bark, pine needles, rough compost, or municipal compost mixtures such as Cedar Grove Compost, or Tagro.) Don't let the mulch heap up against the trunk of the plant. Use porous materials and keep the depth at 2 inches or less to avoid smothering the fine roots.
Finally, don't cultivate over the roots of the plants (avoid tearing at the ground with weeding tools.) The fine surface roots are easily damaged.
(link updated 06/08 dp)
Hortsense: Managing plant problems with Integrated Pest Management
