You've seen rhododendrons before, but never like this.
Their showy flowers and handsome foliage run riot over Holden Arboretum's new 4.5-acre Rhododendron Discovery Garden. It seeks to inform visitors about the diversity of this plant family, how new varieties are created and how to best grow them at home.
It's Holden's first major project since 2002, and is the result of a $7.5 million Phase 1 capital campaign -- the largest such campaign in Holden history.
Get a first look at the new $1.6 million garden during "Shades of Brilliance," a free celebration with entertainment, food and family activities on Saturday, May 18.
Rhododendrons are not new to Holden; the public garden has showcased these blooms in its Helen S. Layer Rhododendron Display Garden. So why build another rhododendron garden?
IF YOU GO
- Rhododendron Discovery Garden
- What:
- Holden Arboretum's new $1.6 million garden opens to the public with "Shades of Brilliance," a free celebration, and "Rhodies After Dark," a ticketed party.
- When:
- "Shades of Brilliance," 11 a.m.-4 p.m.; "Rhodies After Dark," 7-10 p.m. Both on Saturday, May 18.
- Where:
- 9500 Sperry Road, Kirtland. Tickets: $55 per person or $90 per couple for "Rhodies After Dark." Go to
- holdenarb.org
- or call 440-946-4400. Deadline for reservations is Wednesday.
The answer is that the two gardens fulfill different purposes, said Holden president and CEO Clement Hamilton. As nice as the old rhododendron garden is, "It wasn't set up to tell stories," Hamilton said. In the new garden, filled with interpretive panels, "you'd have to work hard not to learn anything."
One big lesson to be learned is that rhododendrons, azaleas, Japanese andromeda and mountain laurel belong to the heath family of plants. These botanical cousins will grow side-by-side in the Discovery Garden as living evidence of the family's variety.
There are more than 1,000 species of rhododendrons. Some have footlong leaves and huge, ball-shaped flowers. Others produce leaves smaller than a pinkie fingernail and flowers the size of a pinhead.
"It shows the diversity out there," said Roger Gettig, director of horticulture and conservation at Holden. "People will be blown away to see rhododendrons with leaves that small."
A tree allee planted this spring points the way to the new rhododendron garden. Most tree allees, or avenues, are planted with one type of tree, making them susceptible to disease. Holden's allee is made of various types of trees, including American elm, paperbark hazel from Asia and 'Appalachian Spring' flowering dogwood, which is resistant to a fungal disease that kills native dogwood.
"It will be visually stunning," said Stephen Sedam, senior director of development.
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As with any gardening project, installation began with soil. Rhododendrons and azaleas grow best in slightly acidic and well-drained soil, so more than 4,000 cubic yards of sandy loam were trucked from Madison to form the new flower beds, Sedam said.
Two bio-retention ponds were installed to capture and filter rainwater. Each pond is about 6 feet deep and lined with 8 feet of sand. Underground drainage pipes under the Discovery Garden will direct water into the ponds. After rains, water will slowly leach through the sand and into the surrounding ground.
Wetlands species that can tolerate dry conditions -- bald cypress, winterberry holly and summersweet-- were planted around the retention ponds.
The Discovery Garden also highlights how Holden horticulturalists breed plants for color, hardiness and disease-resistance. 'Holden Solar Flare' and 'Holden Spring Herald,' two rhododendron varieties developed at Holden's research facility, will be on view. Parent plants and their offspring will grow side-by-side to invite comparisons.
It's all part of Holden's goal of becoming an educational institution as well as presenting nature's diversity in a lovely setting.
"A good garden should be beautiful, have unusual plants and tell stories. Just like a good museum exhibit," Hamilton said.
Here are tips on growing rhododendrons and azaleas, from the Holden Arboretum:
Assess your site: Consider year-round weather conditions. Winter winds can damage the plants. If your site is too exposed, group plants together to help break the wind.
Soil drainage: These plants need well-drained soil. To test the drainage of your soil, dig a small hole and fill it with water. If the water remains after an hour, your soil has poor drainage. Add coarse sand -- not builders or play sand -- to the soil. Aged tree bark, fine wood chips and compost also improve the soil and add nutrients.
Soil pH: This is the measure of soil acidity or alkalinity. Rhododendrons and azaleas prefer acidic soils. If you want to plant near a sidewalk or building, be aware that cement and concrete can leach lime into the soil, making it more alkaline. Test your soil to see if you need to adjust the pH. Contact your local county extension service to find a lab, or test it yourself with kits sold at garden stores.
Add sulphur or iron sulphate to increase soil acidity.
Selecting a plant: Large-leafed rhododendrons do best in shadier sites; small-leafed plants can take more sun. Rhododendrons like morning sun with dappled afternoon shade. Azaleas prefer more sun.
Planting: Create a raised bed to improve drainage. Set the plant so that the root flare -- the area of the trunk where the roots begin to flare out --is just above the soil. Put a 2-3 inch layer of mulch around the plant to retain moisture and insulate roots.
Care: Until the first winter, water every four days that your new plants go without an inch of rain. Tap water can raise the pH of your soil; use rain from a rain barrel if you can. These plants are adapted to low fertilizer in the soil. Use a product for acid-loving plants and fertilize in early spring before the flowers bloom.