On Selecting a Site for a Rhododendron Garden
These notes are written particularly for conditions as found west of the Cascade Mountains in Oregon and Washington. They deal more with conditions which affect the welfare of the genus and less with conditions which affect the appearance of the garden.
A site which has fewer late spring frosts and fewer early fall frosts than average would be desirable. A planting close to trees, particularly evergreen trees, is apt to be freer from frosts than it would be without the trees.
The effect the typography of a site has on the severity of late spring frosts is very tricky to determine. The writer will attempt a few guesses as to the relative amount of late frosts that several types of location might. have. We will consider a narrow canyon with a slight grade, say two per cent or less, down its bottom to the outlet, and with thickets along its course. It is possible that that section of the canyon a half mile or more from its out let might be filled with frost with the surrounding area warmer. At the same time the upper slopes of the lower section of this canyon might be relatively frost free if it empties into a low wide area, as for instance, a river with its low lands.
The upper slopes of the sides of a wide valley are very apt to be comparatively free of frost, while a flat bench half way up a long slope could be a frost pocket, even though there may be nothing to hinder the air from flowing horizontally over the edge of the bench.
A site that is free of strong winds has much in its favor as a desirable place to grow rhododendrons. Strong winds can damage or even blow leaves from the shrubs, especially the large leaved types. Steady strong winds can distort the shape. of the developing trusses and new growths, and drastically shorten the flowering period. It is also much more pleasant to be in a windless garden on a cool day than in a windy one. The sure way to determine the comparative windiness of a location, of course, is to visit the place when the wind is blowing.
A site with a thick stand of trees has advantages and disadvantages. The disadvantage lies in the work and expense necessary to remove the trees not wanted. One advantage of a cover of trees is that, a selection can be made. About the right amount of. shade can be obtained where it is wanted if a careful check is made of the shadows cast by different trees at the time of day when and where the shade is needed.
If the land to be used for a rhododendron garden is covered with trees, the development can be made by stages, while the balance is left in its native state, which might be-quite attractive, while open land if not cared for, will grow up in grass and weeds, and present an unsightly appearance. Thick native growth is apt to have in it woodland flowers and ferns which might be preserved, and they would enhance the beauty of the planting. Also in the woodland, the gardener would find fewer weeds and less grass, and of course, fewer undesirable seeds in the ground.
In western Oregon and Washington, the soil on which fir ( Pseudotsuga taxifolia ) trees grow is apt to be from fair to very good for rhododendrons. While our native oak ( Quercus garryana ) is a first class tree to leave in a garden, the soil under it is very often a stiff clay and poorly drained, and it might entail considerable work and expense to remedy the situation.
Land which slopes to the north or to the east is desirable, because the sun's rays hit it at more of an angle, thus keeping the ground cooler in summer. Trees will cast their shadows farther down the hill and allow planting farther away from the roots, and the plants will have better overhead light. Land that slopes to the south or west is, I believe, less desirable for the culture of rhododendrons than would be level land.
An attempt should be made to determine whether the land is well drained or not. If a hole is dug eighteen inches deep and is found to contain no water two days after a heavy rain in the middle of winter, the land may be considered adequately drained. Because land slopes, it is not an assurance that it has good drainage. It may be seepy all winter which condition may be harder to correct than would be a wet condition on flat or nearly flat land. Satisfactory drainage is not likely to be obtained by digging down and hoping to strike a porous formation in a few feet, through which to drain excess water. An outlet has to be made, and the surest way is to install agricultural tile on a grade to an outlet at a lower level. The water enters the tile and flows away by gravity. A hole in the ground partly filled with broken pots will almost invariably fill up with water and stay full as long as the surrounding ground is full. Depend on an outlet for the water, rather than on broken pots.
An adjacent body of water or a stream benefits a rhododendron planting by keeping the humidity higher than it otherwise would be, and of course, water has great landscape value. A stream of water with even a very insignificant summer flow can, in most cases, be developed into pond which will add to the desirability of a bit of land as a home and garden spot.
A site having a majority of the desirable features mentioned, could be developed into an excellent rhododendron garden, and the near perfect site is here in our hills and valleys waiting to be found.