When it's hot and dry, rock gardens thrive

In a changing Maryland climate, gardeners seek the drought-tolerant

In The Garden

August 11, 2002|By Lucie L. Snodgrass | Lucie L. Snodgrass,Special to the Sun

Maryland's unrelenting drought has gardeners questioning the wisdom of planting thirsty annuals and perennials. Autumn gardeners should be equally cautious and consider putting in drought-tolerant perennials, like rock garden plants, for next year.

What exactly is a rock garden plant? It doesn't have to be an alpine plant, according to Baldassare Mineo, one of America's pre-eminent rock garden experts and the author of Rock Garden Plants: A Color Encyclopedia (Timber Press, 1999). Rather, he says, "A rock garden plant looks good growing among rocks." While there are many types of rock gardens in different climates and in varying soils, he says, the plants in them all share some characteristics:

* They are generally no higher than 24 inches.

* They do best in areas that have excellent drainage, such as hills or slopes.

* They typically require less water than more traditional garden perennials.

Rock garden plants also take advantage of their surroundings in ways that most plants can't. "Planting with rocks of medium size acts as one of the best mulches on earth," Mineo says.

Gardeners who don't have the time or space to create a full-scale rock garden can still reap many of its benefits in traditional beds by planting around a few well-chosen rocks. Most rock garden plants, like sedums, require very little topsoil to begin with, and will thrive almost anywhere, including in the front of most well-drained borders. And because rock garden plants are typically smaller than the perennials found in traditional garden beds, it's possible to plant many varieties and species of plants in a small area.

Maryland is an especially good place for rock garden plants. Our hot and increasingly dry summers are well suited for alpines like Sempervivum (commonly known as hens and chicks or houseleek) and Thymus (thyme), which, though not native to the area, come in a wide array of varieties and colors; are hardy in our winters, require little or no water and spread quickly to form green carpets over large surfaces. Other rock garden plants that work well here are miniature varieties of common species like Dianthus, Penstemon, Phlox, Gentiana and Iris.

Dr. John White, professor emeritus of horticulture at Penn State University and a leading researcher on drought-tolerant plants, sees a measurable movement toward rock-garden plants. "There is a trend toward growing perennials and away from annuals. And, there is a fairly high concentration in rock garden plants." White attributes the growing popularity of rock gardens and their plants to changing weather patterns and lower rainfalls. Thirsty plants that require daily care, deep soil and heavy watering are increasingly being dropped from must-have lists for gardeners. Instead, he says, they are gravitating toward low-maintenance plants, including natives like Lewisia, as well as xeriscapic plants, which store water in their leaves.

Fortunately, information on rock garden plants is abundant and easy to find. The North American Rock Garden Society (NARGS) has thousands of members and dozens of local chapters across America. The society's excellent Web site (www.nargs.org) is filled with information on everything from which plants to select for our area to more detailed information on constructing entire rock gardens.

Plant selection can be done at some local nurseries and through the mail. Consult with an expert, if need be, to ensure that you pick appropriate plants for your location. Try, also, to achieve a relaxed and even random look in your garden. Avoid perfectly spaced clumps of plants and geometrically arranged rocks. Instead, go for an effect that nature might create: drifts of plants surrounding and growing in rocks, and plenty of low spreaders like phlox and creeping thyme.

In our area, one of the best reasons to choose rock gardens plants is that they are relatively low maintenance. Once you've placed your rocks, put in your plants and made sure they are watered enough to get established, they can pretty much be left alone. Because they grow low to the ground and spread in and around rock outcroppings, they leave little room for weeds to grow. And since they require so little water (which encourages weeds), gardeners don't have to worry about wasting that precious resource to keep them alive.

For more information

WEB SITES

The North American Rock Garden Society, www.nargs.org

www.alpinegardensociety. org

www.backyardgardener.com / mttahoma

BOOKS

Rock Garden Plants: A Color Encyclopedia by Baldassare Mineo (Timber Press, $59.95)

Alpines: The Illustrated Dictionary by Clive Innes (Timber Press, $39.95)

Stone Rock & Gravel: Natural Features for Modern Gardens by Kathryn Bradley-Hole (Sterling Publishing Co., $19.95)

SEED AND PLANT SUPPLIERS

* Siskiyou Rare Plant Nursery

2825 Cummings Road

Medford, OR 97501

541-772-6846

www.siskiyourareplant nursery.com

* Fieldstone Gardens, Inc.

620 Quaker Lane

Vassalboro, ME 04989

207-923-3836

www.fieldstonegardens. com

* Niche Gardens

1111 Dawson Road

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