Tips for Beginners: Winter Hardening Rhododendrons
Reprinted from the Quarterly Bulletin of the American Rhododendron Society, Vol. 3, No. 1:10-12.
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 [winter] 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 [author not published] 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 ...For many years nurserymen, growers, and gardeners [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...In most parts of the country this treatment is doubly foolish. What is taking place within the plant? All available moisture has been expirated 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...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.