By Island County Extension Agent, Donald B. Meehan
SELECTING HARDY RHODODENDRONS FOR ISLAND LIVING
The last two years have been hard ones for most plants in our area. Species which normally do well in our climate have suffered a great deal. Many of our Rhododendrons have been in this group. The combination of hot, dry summers and extremely cold winters has brought on a lot of stress and damage to many Rhody varieties which are less hardy.
Often we are not familiar with a plant's hardiness at the time of purchase. We assume it will do well simply on the basis that wild Rhododendrons grow readily in our island maritime climate.
Rhododendron varieties have a wide range of cold hardiness. For example, those varieties such as the hybrid R. America and R. Pioneer are tolerant to minus 20 degrees F. Other varieties do not withstand temperatures below plus 15 degrees F. When selecting a variety for your micro-climate be as concerned about cold hardiness as you are about color and shape.
Here are some tips on growing Rhododendrons in Island County. They are from WSU-Master Gardeners, Don Milliken and Bob Alway, both belong to the Whidbey Island Chapter of the American Rhododendron Society.
Rhododendrons can be planted or transplanted almost any time of the year on Whidbey Island, but early spring and early fall are best. Rhododendrons require acid soil rich in organic matter and draining well.
Does your soil drain well? To find out, dig a hole a foot or more in depth and fill it with water; if the water is gone in an hour, fine. If not, there is too much clay or hardpan.
In such soil, any hole that is dug becomes a basin, holding water instead of draining well and will drown the roots of any Rhody placed in it. Conditions can be improved by a raised bed, 10 to 12 inches above ground level and adding peat moss until the soil becomes friable. NEVER plant the root ball deeper than it was at the nursery.
Start by selecting named varieties of Rhododendrons. Clones grown from cuttings of plants with known qualities of hardiness, blossom season and color, foliage growth habit and size at ten years.
Rhododendron nursery plants are available as very small plants without flower buds or with buds formed. Be sure of what you are selecting so you know what to expect the first season.
Mature plant sizes vary from dwarf, 18 inches, to tall, 6 feet or more. Consider what you want to plant and where. Dwarf plants can be used as a border and taller plants as background in either sun or shade. A location with morning sun or late afternoon sun will also determine which variety should be selected. A site providing morning sun and very late afternoon sun with filtered light during the hottest part of the day is a near-perfect location for most Rhodies. Some Rhodies prefer full sun.
Rhododendrons are shallow-rooted. They dry out easily in the summer. The roots are very fine and only slowly move into the surrounding soil. Watering should take place on the root ball and near the drip line. This is especially important for first-year plants.
When weeds appear, pull them. Do not cultivate and damage the shallow roots. Mulch with fir needles, ground bark or chips; the coarser the better for good movement of air and moisture to the roots. Plants placed against the south wall or under eaves are subject to over-heating and lack of moisture.
Planting in soil rich in organic matter will allow Rhodies to grow well without fertilization. The soil needs to be acid to provide the best growing environment. Protection from drying winds will improve the performance of even adapted varieties. Severe freezes plus wind may be less damaging if the plants are well watered and mulched before the first fall freeze.
Normally pruning is not a big priority. Some pruning can be done to establish better form. The practice of dead-heading is desirable with large-flowered plants. This is done by breaking the truss (the central axis of the bloom cluster) free with a quick snap of the thumb and pressing on one side. Dead-heading will reduce potential disease from attacking the plant and it will help to add vigor to the plant for producing limbs and leaves instead of seed pods.
For those who want to learn more about the culture of these beautiful plants, contact the Extension office for a list of publications available from WSU covering Rhododendrons. These publications provide information about hardiness, color and size. Most are available at a minimal fee.
From time to time I have had individuals ask me if it was permissible to collect wild Rhododendrons seen growing along the highway. After a short visit with the Prosecuting Attorney it was clear to me that to do so would be a violation of the law.
A cursory survey of the laws related to the collection of plant materials failed to show any particular laws prohibiting such activity with regard to Rhodies. However, there exist specific laws which expressly prohibit the removal of any items "affixed" to property you do not own. Since Rhodies are "affixed" then we must assume it is illegal to remove them from government or private property.
Many of you are not aware of the Meerkerk Rhododendron Garden near Greenbank. This amazing garden opens each year to the public during the bloom season. It displays a great number of unusual Rhodies. It can be found by turning east onto Resort Road south of Greenbank and traveling about a quarter of a mile. A small sign marks the road leading to the Garden. The Public is allowed in from 10 am to 5 pm on Wednesdays, Saturdays and Sundays. The Garden officially opens the beginning of April and will close at the end of June.
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