ELK RIDGE GARDEN
Telephone: 918-791-1733
Email Elk Ridge Garden


GUIDED TOURS

Group tours are available for a fee of $10 per person with a $75 minimum.
Groups wishing to schedule a tour should call 918-791-1733
for more information.

ACCESS
The garden has a half mile of walk ways, with many steps, and is thus not wheel chair accessable.

Grand Lake Weather Report

Research Projects

Rhododendron Test In Oklahoma

Some twenty years ago John Thornton DVM from Franklinton, La. begin to cross rhododendron hyperythrum, a species from Taiwan with other species and hybrids. During the late 80’s I purchased named varieties and seedlings from Dr. Thornton to improve my success with rhododendrons in Grove, Oklahoma. By 1997, I had sixty rhododendron hyperythrum hybrids growing here, many of the more tender plants died from a minus twelve winter. These hybrids and two hundred commercial rhododendrons were planted at Lendonwood Gardens. While I replaced many of the commercial plants with newer varieties which died from the heat, the hyperythrum hybrids were not bothered by the summer heat. H.A.J. Hoitink and A. F. Schmitthenner from Ohio State University in 1974 showed that rhododendron hyperythrum was resistant to Phythoria or root rot. They found that hard wood bark and pine bark aided in the suppression of root rot.  Since R. hyperythrum is resistant to the disease a few of these plants were planted in the ground with no amendments and they grew equally well. Most of the rhododendrons are planted in a mixture of sand and composted pine bark. Peat moss was not used as the moss holds to much moisture especially in the winter and it is thought to encourage root rot.

Over the last thirty seven years, I have planted commercial available rhododendrons selecting those that were thought to be hardy in zone 5 and 6. Thanks to many hybridizers that have introduced new cultivars, I have been able to plants over 750 varieties here at Elk Ridge Garden and the two public gardens that I have built; Lendonwood Gardens and Satsuki Garden.
 
Local whole sell nurseries do not grow rhododendrons because of heavy losses sustained by growing rhododendrons in containers in our climate. However local retail nurseries offered cultivars that are not heat tolerant or susceptible to root rot. I observed rhododendrons in pots would die in the summer waiting for a customer. The nurseryman often would say ‘rhododendrons will not grow here’.

I decided to test hyperythrum hybrids and commercial plants in containers here at Elk Ridge Garden. My location is twelve miles east of Lendonwood Garden and three degrees cooler on the average. This would be a heat test observing the plants at the end of the summer.  I hypothesized that it was the higher soil temperatures that was damaging to the plants in containers, while many cultivars grew happily in the cooler ground.

I selected the best of the seedlings from Lendonwood and took cuttings. I sent them to Van Veen Nursery for rooting and to Dover Nursery for growing. They were potted in two gallon containers and sent back to Oklahoma when they were two years old.   After the arrival in Oklahoma they where subjected to an unwelcome freeze. Briggs Nursery of Washington donated six varieties (10 each) that were growing at Lendonwood to be a party in the study. These plants did not freeze. These selections were of varieties that are often sold to growers or nurseries in the Midwest and East. They were potted with pine bark in two gallon containers, fertilized, watered and placed in light shade.

Results;
Hyperythrum hybrids (ten cultivars) had 96% success – Commercial plants had 66% success

R. ‘English Roseum’-50%
R. ‘Emma and May’-50%
R. ‘Very Berry’-100%
R. ‘Holden’-100%
R. ‘Yaku Prince’-100%
R. ‘Capistrano’-0%

This test for heat tolerance on a few cultivars is a picture of what can be done if heat tolerant rhododendrons were sold and or grown in this climate. Many plants are adaptable to our hot summers and they should be sought out to be grown or sold in the South and the Midwest.    

Len Miller DDS
www.elkridgegarden.com

Reference:

  1. H.A.J. Hoitink and A.F. Schmitthenner 1974 Resistant Rhododendron Species and Hybrids. Plant Disease Reporter Vol. 58 issue 7, page 650-653.
  2. H.A.J. Hoitink and A.F. Schmitthenner 1975 ARS Bulletin Vol. 29 winter issue page 37-41.