QBARS - v14n4 Rhododendron Notes

Rhododendron Notes

The weather continues to provide material for our "notes" as well as our conversation. On June l, we had a temperature of 105 degrees in Alameda County, California, the highest June temperature on record. This high temperature did much damage to the new growth on our plants. In our garden the hardest hit were davidsonianum , 'Lady Chamberlain', spinuliferum , tephropeplum , and daphne , with two to four inches of growth killed.

Leaves on many plants were badly burned and are still unsightly in September. On some old plants the new growth was burned and on others the old leaves were burned and the new growth escaped.

In a neighbor's garden some plants were so heavily burned they looked as if they had been in a fire and two were killed. This damage was typical of that experienced in many other gardens. It was however the only bad sunburn experienced in the past 12 years.

We made a camping trip into the Sierra Nevada Mountains in August. On the Middle Fork of the Tuolumne River at about 4000 feet there is a heavy growth of Rhododendron occidentale growing along the banks of the stream. The blooming season was over for most of the plants but there were many still in full bloom on July 20, 1960. These flowers about 1" in diameter and all white, except for a small blotch of pale Indian Yellow. This information will supplement the fine article on our Western Azaleas by E. P. Breakey in the July Quarterly.

Our rhododendrons and deciduous azaleas have had a splendid bud set this summer and should have a fine flower display in 1961.

- E. H. Long, Oakland, California

The species section of "Rhododendrons for Your Garden" to be published in the spring of 1961, is almost completed. This section will for the first time give American experience in growing species rhododendrons and evaluate them in accordance with their performance here. Many experienced growers from all parts of this country greatly helped by sending in detailed report cards. The committee of Cecil Smith, George Grace, Howard Slonecker, Mrs. Ruth Hansen and Rudolph Henny, who compiled the information from the cards, all have wide experience over many years in growing species and the many hours they worked in making the information as accurate and complete as possible greatly helped the writer in writing the material from their report sheets. The species section will cover about 100 pages and should be worth the price of the book.

The "colors" of green always surprise and make one realize how important they are to good landscaping. All the shades of green; grey, blue, light and dark make the garden a picture during the many months of the year when plants are out of bloom. Add the shapes and sizes of leaves and many growth habits of shrubs and trees and you get beauty instead of monotony in the garden. Even the most lanky shrub or misshapen tree often has a definite place. It is rather .. wonderful to think that the rhododendron family alone can bring most of these variations to the garden. That could be expanded to a very interesting story. It needs writing. I know the editor would greatly appreciate material of this type and the members would like to read it. It would make your Bulletin more interesting.

This matter of "sawdust" for mulches or for incorporating into soil where rhododendrons are to be planted, still often arises. It has been proved not only by agricultural colleges but in actual practice over many years in nurseries and in gardens that here in the northwest sawdust is our best mulch. And when incorporated into soil it does much good, even raw fresh sawdust direct from the mill. Sawdust for a mulch is universally used throughout the northwest, more so than any other mulching material, and it has been so used for many years. Nurseries, who just can't afford NOT to grow good plants rototill fresh sawdust several inches deep into the soil and half an hour later plant in the same soil liners direct from the greenhouse. We have seen it done many times and we have never seen bigger or better roots on rhododendrons than some grown in soil which over a period of years is half sawdust. Certainly more nitrogen fertilizer must be used and you must be careful of the amount used. Good gardeners usually play safe by making several light applications of strong fertilizers instead of a heavy one. Plants the first winter may turn somewhat yellow but quickly "green up" again when fertilizer is applied early in spring. We have never seen damage done by coarse raw sawdust when it was not used to excess, to rhododendrons or other plants and bulbs.

In colder sections mulching plants for winter protection is common practice. In the northwest also it is advisable. Rhododendron roots grow partially on the surface of the ground, these fine hair roots are protected against winter cold and summer heat by a good mulch. A mulch applied to rhododendrons should not be removed unless applied very deep for winter protection, and then only partially removed. Just over winter hair roots will begin growing into the mulching material and these roots need protection all year. Most plants benefit in many ways from a loose mulching material. Leaves, particularly oak leaves, are good, pine or fir needles, very old rotted manure, light compost and of course sawdust are all good mulching materials.

R. camtschaticum R. camtschaticum
Fig. 36. R. camtschaticum , an
interesting deciduous plant from
North East Asia growing well in a
rocky location.
Bovee photo
Fig. 37. R. camtschaticum
Bovee photo

A most interesting species in our garden is R. camtschaticum (Fig. 36), a tough deciduous rhododendron from Siberia, which will take anything winter offers. But here in the northwest it does demand excellent drainage, light shade and moisture during hot summer weather. R. camtschaticum flowers on young wood, unique among rhododendrons. It forms a tight compact plant some six or eight inches high. Our plant which was grown from seed some ten years ago now covers an area of 3 ft. by 2 ft. The flowers are solitary appearing on short flower stalks, about one inch broad, a good rose-purple with attractive markings on the upper petal of the flower. It blooms in late May or early June and usually will set a bud or two on plants two years old from cuttings. It has proved to be an easy grower for us and is one of the most talked about dwarfs in our collection.

- Bob Bovee, Portland, Oregon

To those of us in the Eastern United States whose Rhododendron flowering season is not as extended as some other areas of the globe, the occasional flowers of some hybrids, off-season, is a distinct pleasure. In mid-August, a dozen or so flowers of the mucronatum clone R. 'Magnifica', with its fresh pink and white bloom, are in the living room with greens. This plant puts out flowers a few at a time, throughout much of August.

To mulch or not to mulch...regardless of the controversy, the fragrance of pine needles in hot sun, coupled with the seedlings that sprout convexa holly, yew, pine, bloodroot, jack-in-the-pulpit-are an unbeatable combination to me.

Partridgeberry, also known as Twinberry, and more properly as Mitchella repens , is an evergreen mat of tiny rounded dark green leaves, native to the Eastern United States, but extending out as far as Texas in the South. The tiny, white fragrant flowers, shaped like miniature trumpets, appear in pairs. Because the root system is not rampant, the plant makes an excellent ground cover to use with azaleas and rhododendrons.

One of our members, Mr. Raymond P. Jefferis, Jr., told me of an amazing growth in root system in rhododendrons planted last year, which had to be moved this year. A generous handful of perlite, incorporated in the planting with peat, and mixed with the soil, is the reason.

At our flower show in May, Patricia Allison of Morris Arboretum, showed us flowers and microscopic slides of azaleas with petal blight, a disease which has moved up from the South. A number of remedial agents have been tried over the years, and newer and better ones are being developed.

November 10th will be Joseph Gable night, celebrated by a dinner meeting at the Madison House, Presidential Apartments, Philadelphia. The Philadelphia Chapter would like to extend an invitation to members of any and all Chapters near enough to join us in honoring Mr. Gable. Will anyone interested in joining us please contact me?

- Betsi Kelius, Philadelphia

The Northwest is an area of microclimates which prohibits a blanket recommendation for use of early blooming rhododendrons, this includes a great number of choice species and their hybrids. At the same time, there is a dearth of relatively low growing or slow growing plants for this area in other genera which may be used for fronting down from the large leaved hybrid rhododendrons or in leaf size sequences.

For areas where maddenii members are not out of the question, two versatile, relatively low growing rhododendrons with leaves of a good size for gradation in landscaping are species R. ciliatum and its hybrid R. 'Cilpinense' (x moupinense ). Both may be grown in shade as well as in full sun. Some scorching occurs only during the hottest of summers. They are handsome in rockeries as well as in the border. Their hairy leaves relate them well to heather and they bloom when the winter heathers are at their best. There are pink forms as well as the more common white but the selected color is important only if that color scheme is desired.

Rhododendron ciliatum blooms the latter part of March into April in our garden near salt water in North Seattle and is more likely to escape frost damage on flower buds than R. 'Cilpinense'. We consider it invaluable in its location, as it blooms with Rhododendron 'Christmas Cheer', 'Springwood White' heather and Prunus autumnalis where it is exposed to the Western sun. We also have it growing in a rockery facing West, which is an acid test of a rhododendron.

Rhododendron 'Cilpinense' is a more beautiful plant than Rh. ciliatum but it starts blooming the first part of March and is subject to the killing frosts that may occur generally up until March 15. This last spring we had about six degrees of frost over a period of eight days. About three-fourths of the expanding flower buds were killed, although the leaf buds and foliage were not damaged. Our location is a few degrees warmer than the downtown Seattle reading, so those areas that are colder would have lost all the flowers. We acquired R. 'Cilpinense' after the 1955 freeze and this is the first year the flowers have been damaged, so we feel it is well worth having. It is growing in a Western exposure in combination with Rhododendron augustinii , evergreen huckleberry Vaccinium ovatum and Rhododendron molle hybrids in a bed bordering an expanse of heather.

Another ciliatum hybrid, R. 'Snow Lady' ( leucaspis x ciliatum ?), is similar in appearance to the other two and is also a more beautiful plant than R. ciliatum . The leaves are a darker green than either of the other two, perhaps because we are growing it in light shade, and the flowers are more spectacular as their whiteness is accentuated by black stamens. It is a recent acquisition which we have not tested in the sun and it has bloomed once, starting one week before R. ciliatum .

- Ruth Jacobson, Seattle, Washington

One of the usual complaints of purchasers of rhododendrons is that the plants fail to bloom the year after they were purchased. The trend seems to be for gardeners (or perhaps it is the retailers) to insist on rather small plants that are heavily budded. This means the nurseryman has to grow them under a low level of nutrition in order to set the buds. This, coupled with the loss of roots at digging and transplanting, very frequently interferes with flower bud formation for the following year. From a strictly horticultural standpoint, it would be more logical to buy un-budded plants and get them well established before expecting a real show of flowers. Incidentally, in this part of the country, plants seem to be budding quite well.

Fall flowers on any spring blooming shrub always arouse a considerable amount of interest. We have a few plants of 'Mohamet' which are blooming out freely at the present writing, late in September. I understand this variety frequently produces fall bloom.

Only a very few names have been turned down when referred to the International Registrar. They were rejected for a good reason, usually because they were identical with, or too nearly alike, names already in use. When we consider that the same name was given to as many as six or seven entirely different varieties in the past, we can see that the present registration program is doing a much needed job.

Much has been said and written about propagating media for rooting cuttings of rhododendrons and many other types of plants. In many cases the suggestion is that a mixture be made of peat and sand, peat and vermiculite, or other combinations. In a few cases such mixtures may be superior to either material used alone. We have found, however, that we get excellent rooting in straight peat moss, which saves the trouble of mixing other ingredients with it.

We live in a part of the country where logging is an important industry, and where thousands of tons of sawdust have been burned or dumped into a ravine to rot. Industrial uses for sawdust are increasing, and at the same time gardeners are finding sawdust very useful as a mulch or for lightening heavy soils. The gardener who has a readily available supply of sawdust at a reasonable price is fortunate.

Quite a bit has been written in praise of R. yakushimanum , both as a species plant of value, and as a possible parent for hybridization. These comments were apparently justified as two seedlings of R. yakushimanum received Preliminary Awards from the A.R.S. in 1960.

Plastic pipe of various types now provides a relatively inexpensive method of getting water to where it is needed in the garden. In many cases it may cost very little, if any, more to install permanent plastic pipe with an outlet just where it is needed than it would cost to run an ordinary garden hose on the surface of the ground. Since rhododendrons are shallow rooted, and hence particularly likely to be damaged by dry weather, the installation of permanent sprinklers, where it is convenient to do so, would seem to be worth considering. In some cases such sprinklers will be very useful if operated during periods of extremely hot weather. Sun scald may be prevented by keeping the sprinklers going on the leaves during the hottest part of the day. In some areas where such weather may continue for a relatively long period such sprinkling has to be done with a good deal of caution to avoid water logging the soil.

- J. Harold Clarke, Long Beach, Washington