Azaleas in My Garden
By Joseph Casadevall, Paterson, New Jersey
Most growers and sellers of plants and shrubs for our gardens consider minimum winter temperatures as the limiting factor in selecting plants for specific gardens. Azaleas and rhododendrons are no exception and most nursery lists show minimum temperatures which the plant may be expected to take and remain alive.
Very broadly this is a guide which is easiest to get together. I have come to the conclusion that in many gardens, particularly here in the Northeast, the early termination of the growing season is a very serious problem. Perhaps most serious is the effect it has upon azaleas of the Obtusum Series. My observations deal mainly with plants of this group of the rhododendron class. This discussion will be limited to the hardiest species and hybrids of the group. This report concerns my experiences with these plants in an area about 20 miles northwest of New York City, New York. I am sure that this is a widespread problem, among gardeners and professional growers alike.
Here is an area where the normal winter minimum will seldom go lower than -10° F. and then for short periods, perhaps two or three nights. Some winters the temperature never drops to zero. Above this minimum the species R. kaempferi and R. poukhanense and some of the R. kaempferi x 'Malvatica' hybrids and Mr. Gable's hardiest introduction would be expected to live and flower well. The above plants will set buds if there is no early hard frost until, say November first. Here in my garden this early killing frost may occur anytime after September 15. All small plants and so called tender clones may be killed outright. On other plants regardless of "size" floral buds usually are lost even though this may not be discovered until spring. Plants like the widely grown Azalea 'Hinodegeri' Azalea 'Hino-crimson' can be expected to lose nearly all buds.
Naturally many conditions which vary from season to season and the time and severity of these killing frosts will show some difference in its destructive power. Generally the earlier the frost occurs the more severe will be the damage to wood and floral buds. Plants shaded from the early morning sun seem to suffer a little less than plants in full sun or fully shaded. Here a gradual cooling off with light frost about mid-October and gradually increasing as winter advances seems ideal; weather cannot be ordered and no two autumns are alike. With a gradual hardening up plants like azalea 'Hinodegeri' have come thru -10° with but slight loss of floral buds.
Mr. Warren Baldseifen, a near by propagator of rhododendrons, pointed out to me damaged flower buds on Gables hardiest hybrids. He specifically mentioned that his plants of Azalea Louise Gable will flower in May, all buds not lost too early by autumn frost. Winter temperatures low of -10° have not injured totally unprotected plants of Azalea 'Louise Gable', or Azalea 'Maxwelli Alba' if these plants are sheltered from frost until early November.
I might mention that the following list of azaleas have been the most successful after early frost. I have noted the percentage of floral bud loss as I have recorded for a period of five years. The omission of a plant does not mean that it is not frost resistant. Though I have grown over 150 clones, not all could be grown here due to the large numbers now available. I am noting what I like in each type as best in each color group.
R. kaempferi and R. poukhanense in their hardiest forms have flowered all floral buds even after a 14° frost early in October. I have mentioned hardiest forms because there is a great variation in a group of seedlings. Some plants have lost all buds Some suffered a partial loss. Others retained all in a living condition. I know of no clone of either species now available which is resistant to premature cold snaps as above mentioned.
Of all the clones of hybrids I have tried Azalea 'Louise Gable' has the best quality of flower. All plants will show some flowers, averaging perhaps a 50% bud loss to a hard freeze.
Azaleas 'Elizabeth Gable' and 'Royalty Gable' have shown the greatest number of flowers. Even very small plants will flower over 50% and larger plants may lose but 25% bud loss.
Azaleas 'Mildred Mae' and 'Claret', both Gable's are good for 50% loss.
In reds 'James Gable' and F. 3.G. will how some flowers every spring. 'James Gable' in my opinion has the finest color of any red azaleas I have seen. Both are hose in hose-but here they suffer a 75% floral bud loss. Even very small plants will not wood split though.
I have tried every white available, but not one will even show 10% of its flowers following an early frost. Azalea Ledifolia Alba is noted for its late maturity of wood and floral buds.
Very surprisingly a dainty little Kurume clone 'Daphne' has been flowering every spring for several years now. With no protection from sun, wind, or frost at anytime of the year two small plants have flowered every May.
Mr. David Leach has suggested that "an application of superphosphate, potash, and magnesium at the end of summer will greatly hasten" this hardening off. He also stated that it is available as a Reliance Fall Conditioner.
It must be realized in arriving at the above information some leveling off here and there has been done. Since plants in different parts of the garden will react differently to the same conditions, an average has been sought. The problem is so realistic that plants of Azalea 'Hino-crimson', Azalea 'Hinodegeri', Azalea Ledifolia Alba and many others are brought up from the Southern nurseries by the thousands every spring. If a nurseryman can't flower a plant, what chance has the average gardener who chances are has a less favored location than the nurseryman. Fortunately some will find a spot to their liking and do rather well. But many are doomed to few or no flowers in following springs. Since size of the plant makes no difference when flower buds are exposed, if a plant fails when small, a four or five foot one will also fail under the same conditions, though larger plants are more resistant to splitting of wood.
Some day acclimatized plants will be available and the Northern growers can have some of the splendor which is now known only in Dixie.
I doubt that cultural practices will ever bring this about. These plants will be selected from many thousands of seedlings in some breeder's nursery as were the Glen Dale Hybrids in Washington, D.C., U.S.A.