Kalmia latifolia aka Mountain Laurel

Mountain laurel, Kalmia latifolia, is a broadleaf evergreen shrub in the heath family, Ericaceae. It is native to the eastern United States. Its range runs from Quebec and New Brunswick south to Florida and Louisiana. To the west it reaches Ohio, Tennessee and southern Indiana. In the wild it grows on rocky or sandy woodland, mountain slopes, balds, meadows and forest edges. Other common names include calico bush, spoonwood and sheepkill.

In gardens it forms a dense, rounded shrub, usually 5 to 12 feet (1.5 to 3.7 metres) tall. It spreads about as wide as it grows tall. Growth is slow, and the plant becomes looser and more open with age. On Appalachian slopes it can rarely become a small tree near 32 feet (about 10 metres). Old trunks twist and gnarl, and their red-brown bark cracks and shreds. The leathery, elliptic leaves measure 2 to 5 inches long. They are glossy dark green above and yellow-green below, and they cluster near the shoot tips.

Flowers open from late spring into early summer, mostly in May and June. They form rounded clusters 4 to 6 inches across at the branch ends. Each cup-shaped flower is under 1 inch wide and has five sides. Colours range from white to rose, with purple-red marks inside. The ten stamens sit bent back in small pockets in the petals. A visiting bee releases them, and they spring up to dust it with pollen. Small brown seed capsules follow and stay on the plant through winter. Breeders have produced dozens of cultivars, including dwarf and deep red-budded forms.

The plant prefers cool, moist, acid soil rich in organic matter, with good drainage. Partial shade suits it best. It copes with full sun where the soil stays moist. In deep shade it grows thin and flowers poorly. Heavy clay, wet ground and alkaline soils make it struggle. Mulch keeps the roots cool and damp. Deadhead spent flower clusters, then prune lightly after bloom. Next year's flowers form on old wood. It is hardy in USDA zones 4 to 9 and rates H6 in the UK.

Gardeners use it for massing in borders, foundation beds, woodland plantings and informal hedges. It pairs well with rhododendrons and azaleas. Deer and rabbits usually leave it alone, though deer may browse it in winter. It gives winter cover, and pollinators visit the flowers. The hard, heavy wood was once carved into spoons and tool handles. The leaves give a yellow-tan dye. The plant burns readily, so keep it away from houses in fire-prone areas.

Lace bugs, borers, scale insects and whitefly can attack it. Leaf spots and blights also occur, and leaf spot is worst in damp, heavy shade. Mealybugs, vine weevil and honey fungus are further risks. Exposed, windy sites can scorch the foliage. Every part of the plant is highly poisonous, and it has no food uses. Grayanotoxins in the plant upset the heart, muscles and nerves. It harms dogs, cats, horses and livestock, and small amounts of leaf can kill. Honey from bees that feed heavily on it may poison people.