Eliot and Linda Paine Rhododendron Discovery Garden

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Immerse yourself amongst a beautiful plant group as you stroll through the Eliot and Linda Paine Rhododendron Discovery Garden.

This area hosts three separate vignettes that examine:

  • Rhododendrons in their native habitat.
  • The role Northeast Ohio has played in hybridization.
  • The successful usage of rhododendrons in home landscapes.

American Rhododendron Society Endowment Grant

 While HF&G has decades of Rhododendron hybridization experience and a solid understanding of the cultivars that will persist in our region, soils vary dramatically throughout the HF&G campuses.

In recent years, we have noticed a decline in the health of our collection across our three core rhododendron gardens. The common culprits – root rot and stem dieback – are part of the cause, but even the evergreen and deciduous azaleas have struggled in some gardens. This has led us to believe that disease is not the sole issue.

We have long assumed that the soil traits in our garden beds, most notably drainage, and canopy cover have been the driving abiotic factors that influence the overall health and vigor of our collection but diagnosing plant health problems is not straight forward and many factors have the potential to impact the health of our rhododendron collection. While we have made guesses at potential problems, we have not gathered empirical data to support these assumptions until now.  Thanks to funding from the ARS Endowment Grant, we have started to assess the basic factors that impact the health of our rhododendron collection including soil characteristics, macro and micronutrient compositions, soil drainage, and light level gradients in our gardens.

Collecting soil samples and performing drainage tests are simple tests that can be performed by the home gardener as well.  If you would like to better understand our methods or to try them out in your own garden, please see below:

Soil Samples

We emphasized testing in 43 beds containing Ironclad rhododendrons and those of similar pedigrees at three locations across two campuses:  Layer Rhododendron Garden (THA), Rhododendron Discovery Garden (THA), and Leach Research Station. If you have one plant that looks a little under-the-weather, you will perform this test only once!

Soil sampling methods

  1. Sampling locations occurred randomly throughout the beds
    1. Before each sample, mulch and leaf litter was removed.
    1. Soil samples were obtained using a soil probe. Ten samples were collected within each bed at a sample depth of including the first 8 inches of soil.
    1. All ten soil samples were combined into one bucket to get a composite soil sample for each bed tested.
    1. The combined samples were allowed to air dry on butcher paper at room temperature with no artificial heat.
    1. Once the samples dried, the lumps were crushed to the size of wheat grains mixed well and cleaned of roots and other large pieces of organic debris.
    1. Approximately one pint of the composite samples was placed into a soil sample bag associated with each collection site and mailed to Michigan State University’s Department of Plant, Soil and Microbial Sciences, Soil and Plant Nutrient Laboratory along with required soil submission forms.
    1. We obtained a full report for each bed detailing:
      1.  N, P, K, Ca, S, Mg, B, Mn, Fe, Zn, Cu, Al
      1. pH
      1. Soil texture (approximated by hand texture)
      1. Cation exchange capacity
      1. Base saturation
      1. Organic matter

Drainage Tests:

We are in the process of conducting soil drainage percolation tests at each bed location.

To begin, we dig a hole in each bed using a 4- to 8-inch posthole digger or shovel. The average size of the hole is 12 deep by 12 inches.  All the loose soil material is removed, and the hole is prefilled with water and left for 24 hours.  The following day, the hole is refilled with water to perform the soil drainage percolation test. The water level is measured by laying a straight edge across the top of the hole and a yardstick determines the water level.  We continue to measure the water level every hour until the hole is empty, noting the number of inches the water level drops per hour. Drainage percolation rate is classified into three categories using the following paraments:

  1.  Ideal – 2” per hour, with readings between 1”- 3” generally included
    1.  Poorly drained – less than 1” per hour
    1. Fast draining – drainage is more than 4” per hour

Stay tuned on the website for more information!

Eliot Paine

The Eliot and Linda Paine Rhododendron Garden is named in honor of the Arboretum’s former executive director and his wife. Paine led the Arboretum from 1983 until 1995, and later served on the organization’s board of directors.

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