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updated: 7/8/2018 10:44 AM

How to create a rock garden that looks centuries old

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  • The seed heads of pasque flowers are as pretty as their flowers.

    The seed heads of pasque flowers are as pretty as their flowers.
    Photos Courtesy of Diana Stoll

  • Euphorbia polychroma brightens the rock garden in spring.

    Euphorbia polychroma brightens the rock garden in spring.

 
By Diana Stoll

Take advantage of a sunny, sloping area in the landscape to create a rock garden. Begin by choosing very large rocks that are common to the region and burying more than half of each one in the soil. They will look like they have always been there if they all protrude from the ground at the same angle. Fewer large rocks are better than twice as many small ones.

Fill in the area between rocks with a mix of very well-drained soil. When creating my rock garden, I mixed native soil with peat moss and pea gravel.

Once the bones (or rocks) of the garden are in place, it is time to choose the plants. It's best to select small plants that tuck beside rocks, complementing instead of hiding them. Here is a sampling of perennials perfect for a sunny rock garden.

Rock cress, botanically named Arabis, forms a ground-covering mat of gray-green foliage 8 to 12 inches tall. Small, white flowers blanket the plant in spring. After flowering, plants can be cut back to keep them compact.

Armeria maritima, commonly called sea thrift, is a cutie in flower and foliage. Sweet, pink or white orbs of flowers rise well above charming tufts of dark green, grasslike leaves in spring. If deadheaded, their bloom time can be extended.

Dianthus Rockin' Red is the newest addition to my rock garden. It has been showing off its glowing red, lacy flowers since I planted it in late spring and is showing no signs of stopping. The plant grows up to 2 feet tall and half as wide.

The bright sulfur-yellow flowers (actually bracts) of Euphorbia polychroma, commonly called cushion spurge, glow over a perfect cushion of foliage in the spring rock garden. In fall, the leaves turn red. Bonfire is a cultivar with burgundy-colored foliage most of the season before turning rich red in fall. Both grow up to 18 inches tall and slightly wider.

Candytuft, or Iberis sempervirens, shows off small, bright white flowers in spring. It grows up to 12 inches tall and 18 inches wide. Cut plants back by a third after flowering to keep them compact.

One of the favorites in my rock garden is Iris pumila, commonly known as dwarf iris. It is a miniature version of tall bearded iris with varieties in a rainbow of colors. The blooms in spring are outstanding, but I love it for its swordlike foliage. Once new leaves grow after they have been cut back to a few inches after flowering (and spent flower stalks cut to the ground), they are a striking contrast to other finer-foliaged perennials.

Enjoy a jolt of color when Phlox subulata is in bloom. Flowers in shades of lavender, pink, red, violet or white completely cover the needlelike foliage in spring. Cutting the plant back by half after flowering keeps it compact while spurring on another, but less dramatic, round of flowers. Give creeping phlox some elbow room. It may only grow 6 inches tall but spreads 24 inches wide.

With seed heads as striking as its flowers, pasque flower (Pulsatilla vulgaris) is a must have in sunny rock gardens. Soft purple, bell-shaped flowers turn to silky seed heads. The foliage is also attractive -- soft, hairy and light green. Plants grow 12 inches tall and wide.

A rock garden isn't a rock garden without sedums. They boast distinctive, succulent foliage in a wide range of shapes and colors. Some are ground covers; others grow upright. The bloom time of flower clusters varies depending on cultivar, but many flower in late summer and fall.

Knit the plants in the rock garden together with thyme. Trailing stems of tiny leaves crawl across rocks, softening edges. An added bonus is its fragrant foliage -- delightful when working in the garden.

• Diana Stoll is a horticulturist, garden writer and speaker. She blogs at gardenwithdiana.com.

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