Wildflower is published quarterly by the Wildflower Center. Its content is national in scope with articles about the conservation and use of native plants as well as news from the Wildflower Center. A subscription is provided to Wildflower Center members as a benefit of membership.
How to cope with the ups and downs of gardening on a slope
Article by Julie Bawden-Davis · Photography by Dennis Fagan except where noted
IF THE OWNERS OF THE NEARLY 1-ACRE PROPERTY IN AUSTIN had hired landscape designer and contractor Glee Ingram to build a ski slope, her job would have been easy. However, what they wanted on the 300-foot-deep hillside property that is a steady 20 percent drop from top to bottom was an environmentally sound haven for themselves and area wildlife.
“When I initially saw the property, I was challenged and perplexed. It wasn’t traversable and contained an overgrowth of exotics with natives clinging for their lives,” says Ingram, owner of Austin-based Growing Designs Custom Landscaping. “Conceptually, the homeowners knew that they wanted to enjoy full use of their steep hillside property, but they couldn’t visualize how that could be accomplished. They trusted me to translate that vision onto the land.”
Ingram worked on the property between 2007 and 2010, producing a stunning hillside garden replete with thriving natives that has attracted attention and was featured on the Wildflower Center’s Gardens On Tour in 2011 as well as KLRU’s “Central Texas Gardener.”
The transformation of the once-hard-to-navigate ski slope to a terraced native retreat was a monumental project.
Ingram’s first task was to free the native plants from the tangle of invasives that covered nearly half of the property. “The property was so covered in tenacious non-natives like true bamboo, heavenly bamboo (Nandina domestica), Ligustrum sp. and Italian jasmine (Jasminum humile) that it was hard to see all of the natives, some of which pre-dated the construction of the original home built in the 1950s,” she says, referring to established trees like escarpment live oak (Quercus fusiformis), shin oak (Quercus sinuata var. breviloba), Texas mountain laurel (Sophora secundiflora), red buckeye (Aesculus pavia), cedar elm (Ulmus crassifolia), evergreen sumac (Rhus virens) and Texas persimmon (Diospyros texana).
After the invasives were removed, Ingram improved navigation on the steep site by creating a 100-foot-long terraced stairway on one side of the house, made from the scattered boulders unearthed during the foundation preparation for the new LEED®-certified home. Later, additional natural boulder steps were created for access to the front upper garden and the pool behind the house. Formal steps of Oklahoma blue slabs (the only imported stone used) with risers of native river boulders were used for access to the garden with tiered stone patios built of recycled stone from the original driveway.
Ingram also created a variety of other destination points throughout the landscape, including an overlook bench in the upper entry garden, a vegetable garden and fruit tree orchard, as well as a deck beside one pool-entry point and a small patio beside another.
In keeping with the owners’ desire to recycle existing materials and promote sustainability, Ingram terraced the hillside of native plants with retaining walls constructed of remnant stone and boulder shards from the site. The walls were installed three to four feet out from the trunks of native trees and dropped down at least a foot. She also amended the soil and added mulch to keep plants moist and healthy.
Ingram designed the garden by clustering natives in patterns so the eye follows a natural course. “I chose native additions to the garden based on their variation in size, shape, form and color, as well as the fact that they would peak at different times of the year so the garden would have more diverse seasonal interest,” she says. “For instance, I added basket grass (Nolina texana) for its draping form, blackfoot daisy (Melampodium leucanthum) for its spring carpet of daisy-like flowers, flame acanthus (Anisacanthus quadrif idus var. wrightii) for its desirability to hummingbirds, coralberry (Symphoricarpos orbiculatus) to attract a wide variety of birds and butterfly weed (Asclepias tuberosa) because the owners also wanted butterflies.” Turk’s cap (Malvaviscus arboreus var. drummondii) became a resident of the garden as well because of its flaming-red summer and fall flowers and its ability to attract birds and butterflies.
“Thanks to the wide variety of natives planted in the garden, the property is a moving palette,” says Ingram. “There are always little surprises popping up. By simulating the natural world, we gave the garden a chance to recover and heal itself, and it’s a welcome retreat for people and wildlife. Now that the trees are healthier, they make a better nesting place for birds, and other animals have flocked to the property, like raccoons, possums and lizards.”
Besides choosing a diverse mix of plants and adding amended soils and top mulch to heal soil that had eroded over the years and been damaged by construction, Ingram feels the retaining walls were the key to bringing the garden back to health.
“All plants on a slope need to be protected from erosion, and slope containment is key,” she says. “Prior to the retaining walls, the natives on the site were hanging on like heroes, and I really respected them, but now that the water collects on the hillside and percolates down the slope, the garden is verdant and the plants are thriving.”