QBARS - v12n2 Factors Influencing Rhododendron Budding and Flowering

Factors Influencing Rhododendron Budding and Flowering

Carl H. Phetteplace, M.D.

This year several members of the Eugene Chapter of the A.R.S. have reported that their plants show an abundance of buds and that if the weather remains favorable, there are prospects for an unusually good rhododendron year. This has been so noticeable as to pose the question as to why there are more buds this year than in the average good year. Several factors influencing budding and flowering are readily observed:

1. Variety

It is well known that certain varieties are prone to bloom heavily year after year regardless almost of the type of season. neriiflorum , for example, is an unfailing bloomer, as are many neriiflorum hybrids. Fargesii is said to be so floriferous in England that if the dead flowers are not picked off, the plant will injure or kill itself from seed production. Discolor , on the other hand, unless grown in a fairly sunny location, may have only a few trusses year after year.

2. Age and size of plant

Anyone who has seen some of the repens hybrids at Rudolph Henny's garden blooming when only two or three inches tall cannot help but be amazed that such a tiny plant can come forth with full sized flowers. Of course, these plants are very young. In contrast, there are in this locality some Barto plants of large size that must be over twenty-five years old that no one yet has seen in flower.

3. Alternate season blooming

There are many rhododendrons which, after doing their best in a handsome display one season, apparently feel the need for a rest the following season although they are very mature and sturdy plants. Notable in this regard are sutchuenense and calophytum . These healthy and happy old Barto plants may be devoid of a single truss following their big year. Attempts at conserving some of their vigor by removing a large number of buds on their blooming years has failed to make much difference and it seems about as well to let them have their own way and flower as abundantly as they wish every second year. These years are worth waiting for.

R. sutchuenense
Fig. 16. R. sutchuenense exhibiting a heavy set of buds.

4. Exposure to sun

Although most rhododendrons do not do well in full sun as plants, it does seem that a rather strong exposure to sun may stimulate more early and free flowering. By the same token, the well shaded plant may become a fine specimen as a plant, but disgustingly indifferent about flowering.

R. rubiginosum R. 'Souv. W. C. Slocock'
Fig. 17. R. rubiginosum heavily budded.
All photos Phetteplace
Fig. 19.  R. 'Souv. W. C. Slocock' after more
than 50 buds had been snapped off earlier.

5. Production of seed

It is said that one seed pod requires seven times as much plant energy and nutriment as one flower. Be that as it may, it is common knowledge that a plant probably will not flower satisfactorily the year following the production of many seeds. It would save us much time and uninteresting labor if all rhododendrons were like R. occidentale in that, for some reason, it will develop almost no seed pods unless hand pollinated. This is fortunate because some of our plants are so large and their flowering invariably so heavy that it would be almost impossible to snap off all the old blooms. If seeds set from all flowers, the plant would surely seriously injure itself.

6. Optimum growing conditions

As already mentioned, too much shade will retard flowering. Likewise a plant that has the most favorable environment, such as good, properly drained soil, adequate protection from hot sun and wind, sufficient moisture and all essential food elements, may seemingly just keep on growing and yet be both tardy and stingy about blooming. Yet the same variety relatively poorly grown may bloom appreciably early. One of our members, who is an excellent grower and hybridizer, used to share some of his little seedlings with a friendly rhododendron rival. The rival would very frequently bloom the new hybrids before their creator did, which resulted in much good natured ribbing. The only comfort the hybridizer had was to declare that he grew his plants much better than the rival and consequently did not get such early flowering. Of course, there was some jest, but possibly a grain of truth as well in this matter that some adverse growing conditions might stimulate a plant to flower somewhat earlier and so, as a short term result, might have something to recommend it. But for the long term, there would seem little doubt but that a well grown plant will eventually be more gratifying, both from the standpoint of quantity and quality of flower.

R. 'Souv. W. C. Slocock' R. thomsonii
Fig. 20.  A small plant of the R. fortunei
series with buds in each terminal after the
freeze in 1955.
Fig. 21. R. thomsonii .  Photo taken in 1958
showing very heavy bud set.

7. Shock or threat to survival

Most of us have at some time had a plant that year after year has failed to bloom until finally we rather rudely removed it to some secondary spot in the garden, little caring if it lived or died, only to find that the next year it bloomed quite respectably. Why does this happen? Is it like the wife, who, it was claimed, must have some periodic abuse and mistreatment from her husband in order to love and adore him? Many observations of this general nature would lead one to consider that the plant, like some human beings, may be stimulated most by adversity or even a threat to existence. Upon some thought, it seems that parallels in regard to this response to adversity can be found throughout all nature. As one observes the many forms of life one sees about him, it is apparent that the first object of life is not the preservation of life itself, but rather the more basic urge of preservation of the species or kind, which, of course, can only be accomplished through the process of reproduction. The flowering of a plant is really not done for our enjoyment, but for the purpose of bearing seed to create new plants of the same kind. In insect, fish and animal life, there are countless examples of the individual regularly either giving up his life or recklessly hazarding it as a response to the urge for reproduction and therefore preservation of the species. And in plant life, there are many instances of this response to insure, if possible, the continuation of kind even at the expense of the life of the individual specimen. Many years ago, my father girdled an aggressive old maple tree in the yard in order to kill it. In its dying year, it was incredibly laden with seeds. Last spring, an old dying cherry tree observed on my way to work had scarcely any leaves at all, but its branches were covered with cherries. By August, the tree was completely dead.

It will be remembered that the winter of 1949-50 was one of our most Midwest-like winters in which there were weeks after the first of January when the ground was covered with snow and the temperatures were unusually low for this area. The following summer all the fir trees were more heavily laden with cones than for many years. It was called a "cone year." There was not another cone year until 1956. All will remember that on November 12, 1955, we had the unseasonable freeze which did so much damage and actually killed many small fir seedlings. Old timber men have told me that they have never seen so many fir cones, rich in seed, as in 1956 following this shock. Of course, we did not have abundant rhododendron flowering in 1950 or 1956 because the cold was so severe that such plants as were not killed outright, sustained more or less damage. Buds were in many instances destroyed or at least maimed, so only a few flowers came out of each truss in some that did manage to make a pretense at blooming. One must remember that the rhododendron buds actually form the season before the year of flowering and must survive the winter months successfully to bloom next spring.

Why then is 1958 a year of exceedingly heavy budding? Has the preceding year contained any serious hardships? In January, 1957, in this particular locality we had a brief, but very severe, bit of weather. It was somewhat variable from one small locality to another. In some areas the temperatures reached several degrees below zero. In these places, many plants were killed outright. In other areas, the temperatures were a few degrees warmer, but still very cold. Generally, it could be said that the plants were subjected to the limit of their tolerance of cold, but in most areas were not severely damaged other than a considerable bud damage. This constituted a real shock which the plants have only this year well recovered from. It would seem that this might be an important factor in accounting for the unusually abundant budding this year on those plants that were not seriously damaged or killed. Another factor may be the unusually nice, sunny year we have had this year. Since the "shock" in January of 1957, we have had one of our most delightful summers, falls, and even the winter, thus far, has been exceedingly mild. It would seem, therefore, that by Mother Nature's having been very rude to our rhododendron family first, and then in turn, being very kind and tender she has brought out the very best prospect we have had in many years. Of course, there is still time for some severe weather to spoil it all, but it seems increasingly unlikely once January is out of the way. As this is written, February first, it seems as you walk about viewing the buds on our plants that we should almost already he making plans for the 1958 Rhododendron Show. It should be a great year. And as an afterthought, perhaps next year will be a period mainly of rest and growth.