Tough as nails

Plants that can tough out the hottest hot and the driest dry are the best. I admire them for their tenacity and ability to stand up to the elements, showing us that even plants of the hot-dry-tough type can be beautiful.

During the early part of June, when temperatures soared and the skies were cloudless, I was repeatedly drawn to the parking area outside the North Carolina Arboretum’s Visitor Education Center. There I found an incredible group of plants rooted in the red-clay soil alongside the pavement, flourishing under the hot, full sun. Grasses, perennials, shrubs and a few trees do a great job of bringing life to parking lots and other harsh landscapes.

Most grasses seem genetically designed to withstand the toughest of environments. With their varying colors and textures, they add a great deal of diversity to any planting. We use a lot of prairie dropseed here at the Arboretum, because it comes from seed easily and works well in production. “Tall Tails” fountain grass quickly taught us how important it is in a small parking lot like ours to give car users space to climb into their vehicles without feeling like nature is also coming along for the ride. If planted, it should be placed at the back of the bed, since it tends to fall over when it blooms.

“Blue Dune” wild rye is a nice spreading plant that sends up a narrow, 3- to 4-foot-tall flower spike. These short-lived plants provide a nice low carpet of blue foliage well into the fall.

For this type of planting, we typically include perennials such as purple coneflower, blanket flower, blazing star, butterfly weed, sedum and goldenrod. “Mini Stella” daylily, the smaller version of “Stella”, is another hardy selection, which may be why we see it used so abundantly by the Department of Transportation in its highway plantings.

The three-lobed coneflower, not commonly seen in most gardens, is listed as a biennial. But it returns year after year at the Arboretum, providing a perpetual show of 3-foot-tall, flowering stems topped with the namesake black cone and yellow-fringed flowers.

The native “Adam’s Needle” yucca, aka “Spanish Bayonet”, brings color and texture to the planting. Like the yucca, sea holly — with its stiff, narrow leaves and bristled margins — adds interest and is suitable for a wide range of habitats, since its native range stretches west from New Jersey to Minnesota and south to Texas and Florida. Planted in the midst of a large sweep of praire dropseed, it provides a nice architectural element and contrasts of textures.

The shrub group in this parking-lot planting is quite impressive and speaks to the durable nature of plants. Cutleaf staghorn sumac is probably the most at home here, as it likes hot, dry weather and well-drained soil. It’s great for naturalizing, as it spreads to form large colonies and adds beauty to the landscape with its spectacular fall foliage.

Bush honeysuckle, a low-growing (3- to 5-feet-tall) suckering shrub, develops arching stems smothered in sulfur-yellow blooms through most of the summer months. This problem-free North Carolina native is at home in the most rugged sites and contributes a sense of grace to a landscape. Old-fashioned weigela is more commonly seen in the shrub border but is pollution-tolerant and does very well in full sun. The dark-burgundy leaves and rose-pink flowers of the “Wine and Roses” variety contrast beautifully with the blue foliage of the “Blue Dune” wild rye.

“Diablo” ninebark is extremely tough and adaptable to most situations. It can grow up to 10 feet tall and is best used in masses or at the back of the border. The red-purple foliage of this variety again provides a nice backdrop and contrast to the gray-green foliage of the zenobia, which is said to prefer moist, well-drained soils but seems to thrive anywhere.

Sweetfern, uncommon and often overlooked, is reminiscent of sumac in its capacity to thrive even in a cut-and-fill site, most likely because of its nitrogen-fixing ability. This low-growing, strongly spreading woody plant is not a fern, as its name implies. But its fernlike leaves are long, narrow and notched along the edges. When the leaf is crushed, it releases a sweet smell, hence the name.

The Rugosa rose has edible rose hips, is pest-free and withstands all types of soils and temperatures. “Blanc Double de Coubert”, a double-white flowering form, is a rose grower’s dream: very fragrant and resistant to black spot and powdery mildew. The “Knock Out” rose is a clean, compact-growing shrub with bright, eye-popping red flowers. The clean foliage of this drought-tolerant beauty turns burgundy in the fall and puts a nice finish on the season.

The main tree used is the adaptable willow oak, which provides nice shade and requires little care. Other trees in the area include white pine, kousa dogwood, sassafras and “Little Gem” magnolia.

In the end, it’s comforting to know that there are so many choices for plants that are tough as nails. Fortunately for us, though, even endurance plants have a softer side that can be highlighted in challenging places such as parking lots. Filling these difficult sites with diverse and colorful plant life is a wonderful thing.

[Allison Arnold is director of horticulture at The North Carolina Arboretum. She can be reached at 665-2492.]