QBARS - v5n2 Rhododendron Planting Observations

Rhododendron Planting Observations

New roots resulting form too deep planting.
Fig. 13: The short annual growth and sparse foliage on this
plant are due to deep planting. Note the formation of a new
set of roots six inches higher on the stem. The plant was
planted eight inches below its root system and made no
growth in several years while a new root system was being
Gifford Photo

Though the criteria of rhododendron culture is somewhat flexible under conditions of divergent soil and climate, the elementary requirements of the plants remain essentially and basically the same. The amount of tolerance within which a plant will grow normally, presuming that most members of the genus are comparably alike is limited.
In all likelihood the most common error in the culture of rhododendrons is deep planting, but here a most pertinent question is raised, just what does constitute deep planting? Is three to four inches of stiff loam or clay that will bake hard, too deep? If the plant is small, say under two feet, or much larger over four or five feet, would that have any bearing? What if the soil is light loam, peat or sandy in texture. Is dense shade a factor? Does the fact that the plant is of dwarf or midget habit make any difference?
All of the above mentioned questions are heard and discussed many, many times. That the factors mentioned are only of more or less importance in themselves they can in combination be a serious deterrent to the well being of the plant.
The perplexity and exasperation of the beginner who faces frustration always arouses wonderment as to why a volume has not been undertaken that will cover the many aspects of the simple undertaking of planting a rhododendron.
I have heard repeatedly from gardeners with many years experience that four inches of earth over the roots of a plant is a bare minimum. There is also a large group that recommend not over one to two inches of root covering. Other gardeners insist that a plant taken from a nursery should have no covering, but should be set without a covering much as it was in the nursery, with the exception of a necessary mulch.
The above advocates were in all cases right, that is in their locality, following cultural practices that under their local conditions came within the tolerance sustained easily by their plants. Ample evidence as to what constituted the correct procedure was apparent and evident by both deep and shallow plantings. In each instance the plants appeared thrifty and most healthy.
Following the assumption that in each case the gardener was following his own safe practices, suppose the plantings were reversed, that is deep plantings made in gardens where only shallow plantings is recommended.
The results would probably answer the debated issue most clearly. i. e. That the gardener that can plant his rhododendron somewhat deeper could successfully grow shallow-planted plants in his location. The reverse would most certainly not be true for the advocate of shallow planting, for even two inches of soil would stunt and hinder his planting.
A plant that repeatedly makes a very short annual growth, assuming that the plant is not old and mature, or a dwarf, should be appraised with suspicion. Such a plant may live for years, just barely holding on in its struggle to adopt itself to incorrect planting. I have dug plants that have been in poor health for a number of years and in riot a few cases have found an entirely new root system being formed six or seven inches above the original roots. (Fig 13) Several years ago a plant in very poor health was called to my attention, the owner related that it had been planted there five years before and during the years had made an aggregate growth of less than two inches. We both inspected the bottom of the plant and found roots near the surface, but after digging up the plant we found that the plant had been planted at least eight inches to deep, and the few roots near the surface had been formed in later years. We trimmed the new system of roots back and replanted, but the plant has not recovered for three years. Mr. P. H. Brydon writing for a California Horticultural Journal some years back relates that while at the University of California he observed mature plants in this same condition. As an Experiment the new roots were removed and in other plants they were permitted to remain. After a number of years all were abandoned as not worth the effort of restoration.
A summary of planting practices, though not given in finality to meet all conditions are advanced.

  1. Well spaded soil made friable either by some means of cultivation or addition of material as leaf mulch or peat moss. When planting the gardener should bear in mind the fibrous root system of the rhododendron his adapted by nature to spread through porous light soil only. Too many times a plant is fitted into the landscape picture under trying soil conditions. An excavation; barely large enough to admit the root system of the plant is made in packed hard soil. Worse yet is the future of such a plant if the soil is clay from the basement, sticky and impervious to water. Plantings of this kind add to the erroneous idiosyncrasies attributed to rhododendrons by unsuccessful gardeners.
  2. I would advocate shallow planting for large plants, and small i. e. dwarf. If the plant is healthy in appearance and has made a good annual growth in the nursery, it can be assumed that planting no deeper is a safe procedure even if conditions are favorable for deeper planting.

Nurserymen many times set a small grafted plant or rooted cutting in a finely worked bed of peat and earth, deeper than usual in order to develop a larger root system and thereby hasten the growth of the plant. This always takes place in early summer when the plant is taking roots and the small plant is in a growing condition. Three inches of this fine material does no harm, for in very few weeks roots have grown to the surface and the plant has adjusted itself. Three to four inches of clay over the roots of the same plant in a wet location a year later can mean trouble for the gardener.  --R. H.