Experience with the Genus Rhododendron In Indiana
H. Roland Schroeder and Stephen Schroeder
In 1969 we became interested in cultivating the Heath (Ericaceae) family because it seemed to be a challenge, especially Rhododendron, including azaleas. There were very few of these plants around and most of them were the old standard Kurume hybrid 'Hinode-giri'. Occasionally you would see R. roseum, Kurume and Gable azaleas shipped from the south that rarely lived over two years. It was generally believed that rhododendrons just didn't live in our climate, and we would have to be satisfied with annuals and the usual shrubs like Taxus, etc. Also about this same time I started raising begonias and was reading a pamphlet about raising begonias from seed. In the first paragraph of the little '"gem" was a sentence that said "remember this is a weed somewhere". This statement ''lit the spark" to challenge the genus Rhododendron.
The climatic conditions here are not conducive to raising rhododendrons as they grow in their native habitat, but with a little understanding we have found it is possible to cultivate the H-1 , H-2 and H-3. However, bud blast occurs three times out of four years on the H-3's. Therefore these gorgeous plants must be protected and given tender loving care.
The azaleas we have raised here all seem to do well provided they are planted correctly. We have Kurumes, Gables, Satsuki, Glenn Dales and one Back Acres hybrid azalea, 'Pat Kraft.' We also raise native American and hybrid deciduous azaleas. It is surprising how difficult it is to collect plants for test plots, but we are hoping things will be opening up soon so we can see just how "tough" some plants are.
The cuttings are rooted under intermittent mist in rooting sheds. We have found the time to take cuttings is when the new leaves just turn to the color of the old ones. This, of course, varies in all sections of the country and in some sections from year to year, so you can't state a given date in the months of May through November. We use peat moss one-half, washed river sand one-fourth, plus perlite one fourth. (Un-washed sand could contain herbicide washed into the river from farmers' fields.) No hormone powder or dip is necessary on the evergreen azaleas, but for rhododendrons and deciduous azaleas various strengths of indolebutyric acid and naphthaleneocitic acid must be used, depending upon the clone.
We are also raising the native deciduous azaleas and have found them difficult to root. However, the rooting percentage seems to be better with cuttings taken from the new growth coming up from around the main trunk. Also they root better if "stuck" two weeks after flowering is over in a medium of peat moss and sand in a '"sweat box" under lights. We use a combination of indolebutyric acid and naphthaleneocitic acid - 2% each with vitamin B1 powder. Also the "natives" can be started from "pencil size" pieces of roots laid horizontally in peat moss, or they can be layered.
In our climate it is necessary to protect the rooted cuttings for two years before actually planting them in the liner beds. It is our belief that azaleas can be planted with the base of the trunk three inches above the ground level with a very solid non-sinking base. If you dig out a shallow depression, fill it with water and it drains away in 30 minutes the drainage is satisfactory. If not, "pea gravel" must be placed in the bottom and packed tightly so the azalea will not sink later. We use half woods soil and half peat moss to fill in around the plant. Woods soil is necessary for the humus and adds mycorrhiza in the soil. Michigan peat is not satisfactory for planting azaleas and rhododendrons in our experience. It is alkaline in nature and conducive to Phytophthora cinnamomi and others of the Phytophthora "clan".
Rhododendron must be planted on top of the ground for best results and filled in and around the root ball with half woods soil and peat moss. The pH should be close to 4.5-5.0 for the rhododendrons and pH 5.0-6.0 for the azaleas.
In a very small area in southern Indiana we have an acid soil, but in the greater part of Indiana pH adjustments must be made to acidify the soil. This is done with ferrous sulfate or sulphur. Especially in the southern half of Indiana we have a severe magnesium deficiency requiring dolomite lime addition and gypsum (calcium sulfate) to the planting soil. Other elements and trace elements seem satisfactory. The gypsum also gives the flowers a richer color and they seem to last longer, besides loosening the soil. Most of iron deficiency here is actually a magnesium deficiency which prevents the assimilation of iron by the plant.
The rain fall is an average of 39-46 inches per year, but this is not distributed throughout the year but comes in "'spurts'". We like our plants to have an average of 0.5 inches of water per week and a two inch mulch of wood chips, pine needles or straw. We do not like to give added water after August for we want the plants to "harden off" for the winter struggle. We have very little snow cover in winter and have alternating freezes and thaws. A low nitrogen, high phosphorous and potassium fertilizer is used in February as top dressing. In nursery beds we use liquid fertilizer from May to July then nothing more that year.
We have bought and have seen plants "pumped" full of fertilizer for looks, and as a "sales pitch", only to have them succumb to the rigors of winter. This practice is to be deplored. Also in the age of container growing it is absolutely necessary to loosen the root ball and have at least 1/4 inch bare roots exposed before planting.
The nursery beds are shaded with 50% shade from June through July and the larger, planted, landscape plants are given 30% shade. The few Dexters we have require more shade than some of the others. Almost all of the azaleas in this latitude will take full sun. Plants that are planted in deep shade do not develop or flower well and should be given maximum sun. We also feel that a plant will very rarely die from Phytophthora if planted in maximum sun - even the most susceptible clones. The Carolinianum Series is our most difficult challenge in respect to Phytophthora. This series must be placed on "pea gravel" and have absolute drainage in full sun. Even then we lose some.
We have an extensive hybridizing program started using the native deciduous azaleas in intercrossing and crossing with the Exbury, Knap Hill and Ilam azaleas. We will be reporting on this project at a later date, but we see possibilities of having azaleas in bloom from April through September and even to the middle of October.
The deciduous azaleas do well here if they have full sun and 1.0 inch of water per week in a good rich humus soil. They are especially fond of well rotted cow manure and are hungry feeders.
In summary "remember it is a weed somewhere" and it will grow in Indiana if enough effort and knowledge is put in force.
We express our sincere thanks to the following "Rhododendronites" for their knowledge and generous contributions to the start of our nursery: Mr. S. C. Early, Mr. and Mrs. Lloyd Hahn, Mr. John W. Neal, Mr. Orlando Pride, Mr. Hideo Suzuki, Dr. John T. Thornton, Mr. and Mrs. Mel Williams and Mr. Edward G. Wood.
Rhododendrons that have been successfully tested for our area include: 'America', 'Nova Zembla', 'Madame Masson'; 'Ice Cube', 'Belle Heller', R. catawbiense album, 'English Roseum', 'Parson's Gloriosum', 'Lavender Queen', 'Holden', 'County of York', R. maximum roseum, 'Candy', 'Rocket', 'Scintillation', 'Janet Blair', 'Cheer', 'Caroline', 'P.J.M.', and 'Windbeam'.
The Evergreen Azalea Committee of the Indianapolis Chapter lists the most suitable evergreen azaleas for our region (Zone 6-B) as follows:
Glen Dale Hybrids - 'Fashion', 'Greeting', 'Vestal', and 'Glacier'. Gable Hybrids - 'Herbert', 'Maryann', 'Mildred Mae', 'Rosebud", 'Purple Splendor', 'Rose Greeley', 'Stewartstonian', 'Boudoir', and 'Susan'. Pride hybrids - 'Jack Stewart', 'Marjorie', 'Nadine', 'Pale Lilac', 'Pride Red', 'Sam' 'Vicky', 'Victoria', 'Watermelon', and 'Winny'. Shammarello Hybrids - 'Desiree', 'Hino-Pink', 'Hino-red', 'Hino-white', 'Elsie Lee', and 'Helen Curtis'. Kaempferi Hybrids - 'Carmen', 'Fedora', 'John Cairns', and 'Othello'. Kurume Hybrids - 'Hino-crimson', 'Snow-White', 'Hinode-giri' and 'Coral Bells'.