On Gardening/State Flower in the Landscape

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University Park, Pa. -- Mountain laurel, Kalmia latifolia is the state flower of Pennsylvania, which grows in many counties. Gardeners observe this attractive native growing on rocky, tree-shaded ledges out in the wild and question why it often fails in a well-maintained landscape.

The answer to that question is that you have to meet the plant's needs.

In the relatively cool conditions of Pennsylvania, most mountain laurel will do quite well in open, woody shade, at the edges of other plantings. Excess wind and hot sun will tend to dry the plants. Optimum conditions are described as full morning sun until about mid-day, followed by shade protection during the hottest portions of the day.

Well-drained and acidic soil conditions are also required for success. Plants will not do well in any soil or location where water collects on the surface or drains slowly out of the soil. Laurels will thrive in raised beds filled with a 12-inch deep mixture of one-third ground pine bark and two-thirds loam soil. Attention to watering after planting and during the first growing season will assure survival.

Like other plants in the acid family, mountain laurel prefers acidic soils with a pH between 5.0 and 5.5. Avoid soils with a pH greater than 6.5 or the plants may not survive.

Laurel can be planted any time the soils are cool and the plants will not dry out. Generally, midfall or early spring are suggested times, especially if container-grown plants are available. The planting hole should be at least three time the width of the root ball and no deeper then its height. Never plant laurel deeper than it grew in the nursery, or set the top of the container root ball below the surround soil grade.

When planting, follow soil test recommendations, if available. Laurel does not require high soil fertility levels. A few handfuls of superphosphate mixed into the backfill soil may be all that is needed at planting. Firm the backfill soil around the root ball and water the plant thoroughly. Cover the planting hole out to several feet beyond with a 3 to 4 inch layer of coarse-textured mulch to keep the roots cool and conserve soil moisture. As with all mulch materials, keep it several inches away from the plant stem to prevent bark damage.

After the plants are established, they should respond to a light application of 10-10-10 fertilizer at a rate of about 1 1/2 cups of material per each 100 square feet of bed area.

Cultivars suited to Pennsylvania include 'Olympic Fire', and 'Sarah' - red-budded with pink flowers; 'Pink Charm', and 'Pink Globe' - pure pinks; and 'Elf' - with white flowers, or 'Minuet' - white with a red band. 'Nathan Hale' is red-budded with glossy foliage. Check with your local garden center for these and other possible cultivars to consider planting.

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Dr. Nuss is a horticulturist at Penn State. He coordinates all extension horticulture programs. He has bachelor's, master's, and doctoral degrees in ornamental horticulture and has been on the Penn State faculty since 1966.