There are six or seven species of Kalmia or Mountain Laurel, ranging from the dwarf K. microphylla to K. latifolia, which can become almost tree-like at about 12 feet under ideal circumstances. Most of the time it will grow slowly, reaching about 5 or 6 feet tall in 20 years or so. All are members of the Ericaceae genus, like Rhododendrons.
Kalmia are native to North America, with a range, depending on species, in the west, from Alaska to central California; in the east from New Brunswick to central Florida, being most prevalent in the Appalachian Mountains, and spreading west to Louisiana, Ohio and Indiana. They require acid soils, but in nature will tolerate a range from moist to dry. In the garden, they want a moist, acid, highly organic soil - just like Rhododendrons. They do not do well in heavy clay or alkaline soils.
As the natural range suggests, most are rated hardy from USDA zones 4 through 9. All parts of Kalmia are poisonous to people and domestic animals, but not to Bambi. While my local herd has nibbled on mine, occasionally, they haven't done a lot of damage.
In the wild, they generally prefer a more open position and disappear as the tree canopy becomes heavier. I my area, clumps of Kalmia in the woods are often called 'laurel hells', which is something I've never figured out since they are so lovely in bloom. In hot areas, they do best with some mid-day and afternoon shade, but prefer at least partial sun. They won't do well or flower well in heavy shade. In northern areas, they can take more sun.
They flower from March to July, depending on location. Their flowers and buds are exquisite; probably among the most beautiful of any shrub. The flower color ranges from white, (photo courtesy of Albion College Vascular Plant Image Gallery) through pinks, (photo courtesy of Florida Wildflower Showcase) to the intense red of Kalmia latifolia 'Ostbo Red'. You can really see the structure of the ribbed buds in the second photo, showing the pink coloration. Another common name for K. latifolia is 'Calico Bush', and you can see where that came from. Kalmia do make a fruit capsule, which is brown and can hang on to the plant over the winter. These are not at all showy.
