abc logo Planting Rhododendrons
Rhododendron ABC's #8

Having selected plants with the proper hardiness and locations that the plants will find compatible, one comes to the actual placing of the plant. The most important thing to keep in mind is that rhododendrons are, basically, shallow rooted plants that seem to require aeration.

Always set the plant so that its root-ball is no lower than it was before it was dug for transplanting. It is preferable to set it even a few inches higher so that it will not settle to an unhealthy depth. I always will remember a sign that George Clarke had at the entrance of his nursery. It read:

WARNING! A PERSON PLANTING A RHODODENDRON TOO DEEP WILL BE REPORTED TO THE NEAREST AUTHORITIES!

I don't know who the authorities were, but there is much truth in the idea behind this warning. A lot of failures in rhododendron culture can be traced to the smothering effects of placing the plant so deep that aeration is impaired. The soil should also contain organic matter, not only to aid in supplying nutrients, but to help keep the medium loose and friable and thus aid in the aeration process. Peat moss, shredded bark, composted leaves and other vegetative materials are good components to add to the planting mixture.

At no time should water be allowed to collect or stand in the planting site, however, rhododendrons need to have the soil around them moist during dry weather. A good way to do this is to use a light mulch of bark or wood chips after planting. Care should be taken not to mix under-decomposed material into the soil when mulching. If this occurs, the tendency is for microorganisms to tie up nutrients, especially nitrogen, so the plants may suffer and take on an unhealthy, yellowish appearance.

As to the use of fertilizer after planting--often it is overdone. Rhododendron fertilizers should be mildly acidic and should be used rather sparingly, twice a year. The first applications -- a sprinkling of the fertilizer lightly over the surface of the planting area -- in March or April just before active growth begins. This application should be relatively high in nitrogen (the first number - for vegetative growth). Remember the NPK numbers (nitrogen, phosphorous and potassium). The second fertilizing should be applied (again sparingly) in late May or June when the second number (phosphorous) should be the highest, when flower buds are being set for the next season and phosphorous is essential for flower bud development.

The whole subject of plant nutrition is more complicated, but it is very important to pay attention to the time of year when the applications are made. Never fertilize after the fourth of July. By midsummer, rhododendrons need to begin to think of dormancy and by autumn should be entering their dormant stage so they will survive periods of low temperatures in winter.

Many plants have been lost because they have still been in active growth when frosts and low temperatures first arrive. Irrigation should be used sparingly as well at that time of year. Of course, some water always needs to be present, but don't keep the plants in active growth when they should be thinking of dormancy arid winter's low temperatures.

One last point in the planting process -- always rough up the root ball before the plant is placed in the planting site. This is necessary to make sure that roots will leave the generally salubrious mixture that they are exposed to in the nursery for the probably less favorable soil conditions of the real world. If the roots do not venture into the surrounding planting site, plants will not thrive and may become stunted and even expire. Making sure the roots are loose and exposed is often overlooked and this can be a source of frustration and failure for both the plant and the grower.

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Dave Goheen