Growing Rhododendrons in the Southeast
Condensed and reprinted by permission, from "American Nurseryman" for Feb. 1, 1964
Recommendations for growing rhododendrons in the southeast were given by two speakers on the program of the nurserymen's short course held at Raleigh, N.C., January 5 to 7, 1964.
William Garren, of the Mountain View Nursery, Travelers Rest, S.C., urged growers in the southeast to be progressive and try some of the new rhododendron hybrids. Declaring that many of the hybrids show wide adaptability, he discussed their propagation and culture in the southeast.
Grafted plants, he said, tend to be rather short-lived; however, some deciduous azaleas are almost impossible to root. In his operation, intermittent mist proved economical and gave much better rooting. Day-night timers, as well as interval timers during the day, proved necessary to keep the foliage moist and prevent wilting of the cuttings. Cuttings taken in September and October tended to root best, and there was some success with cuttings taken in January and February.
He prefers using indolebutyric acid in solution, soaking only the basal wounded area in the IBA solution for 18 hours. Cuttings are usually three to six inches in length. After the overnight soaking, the cuttings are stuck in a mixture of equal parts of sand and peat moss. The cuttings are placed close together so that the petioles of the leaves are not touching the medium.
Rooting Time Varies
Rooting time varies with the variety. Generally it takes two and one-half to four months, he said. Well-rooted plants are removed carefully from the propagating bench to reduce root injury. They are planted in quart containers or growing beds. He warned that transplanting from the propagating bed creates a critical time, because environmental changes are great.
Plants in containers are kept in the greenhouse with high air humidity for at least a month after planting. A high humus content in the soil is essential, he stated. Additions of peat moss, well-rotted sawdust or any other organic matter to soils low in organic matter assure better results. The soil must be acid. Rooted cuttings planted in outdoor beds are planted under shade and misted.
Year-old plants are shifted either to gallon containers or to the fields. Fertilization should be based on soil tests. In his operation, plants are fertilized twice per season with a mixture of one part cottonseed meal to one part 5-10-10 complete fertilizer. Soluble acid fertilizers having an analysis of 30-10-10 are used about every three weeks during the growing period.
Mulch Is Essential
Mr. Garren said that a mulch is essential, for it keeps the soil warmer, in winter and cooler in summer. Mulches decrease the number of weeds, prevent erosion, increase water-holding ability and also continue to break down, adding organic matter to the soil. Oak leaves are kept in bins and applied the next year to a depth of about one and one-half inches around the plants. Water requirements vary greatly, depending on climatic conditions and soils. The grower must learn just when watering is necessary, he said. He recommended a thorough watering whenever an application of water is made.
The second speaker, Mr. Fred Galle, stated that fluctuating winter temperatures, are more often detrimental than extreme temperatures. Through trial and error, the best environmental conditions for particular varieties can be found.
Of more than 200 varieties which he has tested, he was pleased with about 80. Mr. Galle discussed the difficulty of obtaining young plants in the proper condition for planting at Ida Cason Callaway Gardens. Thus, rooted cuttings seem to be the best method of getting started with new varieties. He reiterated Mr. Garren's point about the difficulty of knowing when to water and how much water to give. Prior to using measuring devices to check soil moisture levels, workers at Callaway Gardens watered for three hours. Upon examination they found that water had not penetrated the mulch and that it was necessary to water six hours to have sufficient moisture.
Using slides, Mr. Galle showed and discussed species and hybrids which Callaway Gardens has grown. Usually the yellow, buff and apricot types were most difficult to grow, while the plants derived from species from the lower elevations tended to grow better than those from the higher elevations.
Good plants which he listed to complement a rhododendron planting included ferns, shortia, galax and ardisia.