QBARS - v3n1 Notes on Winter Hardening Rhododendrons

Notes on Winter Hardening Rhododendrons

During the bleak sunless months of Winter, most rhododendrons pass unnoticed in the garden. Since the first early frost of Autumn, the large leaves of the Chinese species seem to droop and draw closer together. The arrival of cooler weather parallels the season of their native home in the high Himalayas. To this prelude the plants react as they have for ages in the past.
Since the last flower buds were formed in the late Summer the plants have done little to all outward appearances. The present period, during the months of December, January and February finds an almost eclipse of cellular activity. Yet, it would be wrong to state that the plant is dormant, for underground even in the dead of Winter new roots are constantly forming. I have observed plants, both large and small being moved throughout the Winter, and almost always the outer perimeter of roots is newly developed. If one has not the occasion to move plants, the new root activity can be easily observed by removing a few inches of mulch. There will be ample evidence, even when the mulch is frozen that the plant is not dormant, for in the warmer earth nature seems to forge right ahead.
The fact that this process of putting forth new roots goes on most of the Winter must plainly mean that the plant is taking what nourishment and moisture it needs, when it needs it. It can hardly be argued that the plant is only establishing its roots into new territory for the coming season. Several years ago I set a small tender species in very rich loam, all contained in a twelve inch clay pot. The plant grew well, with an occasional pinch of 5-10-10 commercial fertilizer, and after I removed it three years later the roots had not left the original root ball. In fact the plant was now thirty inches tall and over two feet across. The original root system measured three inches in diameter. The lapse of three years had seen absolutely no increase in its root system. Since all of the plants were readily at hand the plant made no effort to send roots into new territory for the coming season. A plant will not manufacture a root system for the future, but instead just enough for the requirements and well being of itself for the present.
The foregone brief analysis only brings into more critical focus the indecision of the gardener with regard to late Summer and Autumn watering. For many years nurserymen and growers, and gardeners have recommended the withholding of water during the late Summer months. This supposedly was to afford a "hardening off" period for the forthcoming bout the plant would have with the coming Winter. Many growers and gardeners alike follow exactly this procedure, and the last week in August, when the plant should be storing food, all sources of moisture are stopped. I have seen plants languish, their foliage drooped and in some instances actually burned during this treatment.
In most parts of the country this treatment is doubly foolish. What is taking place within the plant? All available moisture has been expired through the leaves and the reserve sugar, plant food and moisture are also used. In fact, the plant is being introduced to a condition that approaches extinction. If the drought is prolonged all the reserve the plant has stored is thrown into the battle. True the plant is dried out, the food reserves are gone and the plant is hardened. Yes, hardened if one were expected to whittle on it with a pocket knife, but I don't think hardened for a rigorous cold.
In almost all districts there is a period of division of seasons, i.e., Autumn, usually with rains, and almost Summer like days. During this period the ground becomes saturated with moisture and the starved plant immediately gulps all the moisture possible. The leaves again uncurl and raise to a normal position. The plant hurriedly extends its root system and gathers and stores plant food to the brimming.
What point was gained in the dehydrating process? Nature will probably now see to it that the plant assume greater stocks of plant food than before, and if it does not there will remain a close approximation of normality.
Much of the confusion associated with hardiness arises from the growing of small plants, usually by nurserymen. Many are late hybrids, and the unequal root system of a small graft will force it into a late growth. Naturally this late growth will be cut back by the first frost. Many nurserymen abstain from watering to discourage this late growth, but the terminal growth buds will usually start after the first rain anyway.
Real hardiness cannot be implanted into a tender species or hybrid rhododendron by cultural practices. I have often observed neglected and poorly grown plants suffer more from freeze than the well grown plant that has received its proper share of moisture during the Summer.
Any rhododendron plant that is worth growing at all should be grown as well as the gardener can possibly accomplish the feat. Ample and regular irrigation will keep the plant growing well during the dry months of Summer and Fall. When Winter does enter, the rhododendron will be ready. Though it is an established fact that rhododendrons will stand great drought when once established, it must also be remembered that rhododendrons also abhor and evade the arid regions of the earth.