Planting Mountain-laurel

Kalmia latifolia 'Carol'
Kalmia latifolia ‘Carol’ with dark pink flower buds and pale pink flowers.
Joey Williamson, ©2009 HGIC, Clemson Extension

Joey Williamson, Ph.D.
Home & Garden Information Center

Nothing is more exciting in the spring than to see the star-shaped flower buds forming on the spectacular South Carolina native, mountain-laurel (Kalmia latifolia). Mountain-laurels are acid-loving plants in the blueberry family (Ericaceae) and thrive in well-drained soils with morning sunlight. The wild forms of mountain-laurel produce magnificent clusters of white to rose-pink buds that open in May to form 6-inch-diameter corymbs (clusters) of white to pale pink, ¾- to 1-inch flowers.

In their native habitats, these shrubs grow from 7 to 15 feet tall and wide, although older stands may reach 20 to 25 feet tall. However, in the garden setting the typical mature heights and widths of many cultivars are 5 to 8 feet. There also are several dwarf cultivars that reach only 3 or 4 feet tall and wide. These smaller mountain-laurel selections are perfect for the scale of the average landscape setting.

Native white-flowered Kalmia latifolia
The native white-flowered Kalmia latifolia at the South Carolina Botanical Garden.
Joey Williamson, ©2008 HGIC, Clemson Extension

Through breeding of the native forms, many cultivars possess more intense bud and flower colors of reds and pinks. For example, ‘Carol’ is a selection that grows only to 3 feet tall and wide, with dark pink buds that contrast well with its pale pink to almost white flowers. ‘Sarah’ may grow to 4 feet tall and wide and has vivid red buds that open into bright pink flowers.

Kalmia latifolia 'Sarah'
Kalmia latifolia ‘Sarah’ with deep pink flowers at the Pickens County Museum of Art & History.
Joey Williamson, ©2007 HGIC, Clemson Extension

Site selection is very important with mountain-laurels in terms of both light levels and soil moisture. If mountain-laurels are placed in total shade, their growth becomes leggy and flower production is reduced. With excessive sunlight, these natives often show marginal leaf burn from drought injury and sunburn on the foliage, and the plants generally struggle to survive. Afternoon sunlight is too intense for mountain-laurels, so landscape placement should be with morning sun, or with dappled sunlight beneath tall pines.

It is imperative to improve the drainage of heavy clay soils before planting. If an entire planting bed cannot be tilled, then dig individual planting holes 2 to 3 times wider than the plant container and add a soil conditioner made of composted, ground pine bark. The resulting soil mix should be approximately 20 percent pine bark by volume. Mountain-laurels prefer acid soils with a pH of 5.0 to 5.5. While many of the Upstate soils in South Carolina are within this range, it is important that these acid-loving shrubs are not planted in areas that have been recently limed. In addition, with the typically low nutrient levels in South Carolina soils, to enhance root growth and establishment of the plants, a complete organic fertilizer (such as Espoma Holly-tone or Bradfield Organics Acid Adoring Fertilizer) should be added at planting at ½ cup for a 3-gallon-containerized plant and thoroughly mixed with the backfill soil.

Never plant shrubs deeper than the soil level in the container, and with mountain-laurels it is best to place them slightly higher than the surrounding soil. As with all shrubs, mulch the soil with 3 to 4 inches of pine needles or 2 to 3 inches of bark mulch to conserve soil moisture and to keep the soil cooler during the summer. Water the new plant well as soon as planted to settle the soil, and continue to irrigate as needed to maintain soil moisture until established. Try to avoid wetting the foliage when watering the plant.

Mountain-laurels can provide both evergreen color and height to a partially shaded woodland site, and a sense of place to the South Carolina garden. They combine well with many other spring-blooming, native shrubs, such as dwarf witch-alder (Fothergilla gardenii ‘Mt. Airy’), dwarf summersweet (Clethra alnifolia ‘Hummingbird’) and Virginia sweetspire (Itea virginica ‘Henry’s Garnet’). Do consider planting one of the many wonderful mountain-laurels now available. It may turn out to be the focal point of your spring garden.

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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.