Mountain laurel (Kalmia latifolia) is flowering broadleaf evergreen shrub with a gnarly, multi-stemmed growth habit. It has beautiful spring blooms, and its elliptical, glossy deep-green leaves (resembling those of rhododendrons) and gnarled stems make it attractive in all seasons. This shade-loving shrub produces clusters of rose, pink, or white flowers with purple markings in late May to early June. If the flowers are not deadheaded, nondescript brown fruits will appear. Many different cultivars are available that offer various sizes and bloom colors.
Mountain laurel usually grows as a dense, rounded shrub, with branches that grow gnarlier as the shrub ages. It is a relatively slow-growing shrub, adding about 1 foot per year. While mountain laurel is particular about its soil needs, this plant is easy to grow in the right environment. It is a good flowering shrub for mass plantings in shady shrub borders, woodland gardens, or for foundation plantings. It partners well with rhododendrons and azaleas.
|Botanical Name||Kalmia latifolia|
|Common Names||Mountain laurel, ivy bush, spoonwood, calico bush, American laurel|
|Plant Type||Broadleaf evergreen shrub|
|Mature Size||5-15 feet in height, similar spread|
|Sun Exposure||Prefers part shade, but can tolerate full sun|
|Soil Type||Thrives in cool, rich, acidic soil that is moist but well-drained; does not do well in clay|
|Soil pH||5–5.5 (acidic)|
|Bloom Time||Late spring|
|Flower Color||Rose, pink, white; blooms may have purple markings|
|Hardiness Zones||4–9 (USDA)|
|Native Area||Woodlands of eastern North America (New England south to southern Indiana, Louisiana, and the Florida panhandle)|
|Toxicity||All parts highly toxic to animals and humans|
How to Grow Mountain Laurel
Plant mountain laurel shrubs from spring after all danger of frost has passed, to summer. Plant them in soil that is cool, moist but well-drained, and acidic in pH. Space the shrubs 4 to 6 feet apart; they prefer part shade but will tolerate full sun. Avoid windy areas, if possible, especially in the northern part of the hardiness range.
Do not plant these shrubs too deeply. Make sure the shrub's crown (the point where its trunk meets its roots) is not buried. Buried crowns will suffer from rot and your shrub will likely die.
When they are young, keep the shrubs well-watered, and keep the soil moist and acidic by using a layer of wood chips or evergreen bark mulch. Feed the shrubs in spring with a plant food formulated for acid-loving shrubs, such as rhododendron food.
Remove the flower clusters immediately after they have finished blooming. Pruning lightly after the blooming is finished will help keep the shrubs full and bushy.
Mountain Laurel Care
Mountain laurel is highly prized because it performs well in part shade, but deep shade may reduce its flowering and cause leaf spots. In full sun, the deep-green leaves may turn yellowish.
These shrubs like moist but well-drained, acidic soil. Its natural habitat is woodsy areas near swampy zones, but not in soggy soil. It dislikes heavy clay soils. If you have dense soil, consider planting mountain laurel in raised beds filled with a well-draining soil mix.
Ideally, soils should be kept moist, but once established this shrub has fairly good resistance to drought, provided the soil does not overheat. To avoid allowing the roots to get soggy, planting mountain laurel in raised berms or planters can be a good idea.
Temperature and Humidity
Mountain laurel likes soil that is relatively cool, and it will do fine in the warm months provided the soil remains shaded. It normally does not like the high temperatures and dense humidity of southern coastal climates, but some cultivars are somewhat more tolerant of these conditions.
This shrub should be fed in spring with an acid fertilizer, such as that formulated for azaleas and rhododendrons. Feeding will encourage more vigorous blooming.
Is Mountain Laurel Toxic?
Mountain laurel plants contain the chemicals grayanotoxin and arbutin in all parts of the plant, which can cause neurological and gastrointestinal symptoms in people or animals. Even honey made by bees using the pollen of this plant can be toxic. Poison control agencies list this plant as dangerously toxic; the response to any suspected ingestion should be a call to the poison center. Severe human poisoning is rare, but grazing animals are known to feed on it.
Symptoms of Poisoning
Symptoms of mountain laurel ingestion include irregular breathing, anorexia, heavy salivation, watering of the eyes and nose, vomiting, diahrea weakness, convulsions. Severe cases can result in intestinal hemorrhage followed by coma and death.
Varieties of Mountain Laurel
The mountain laurel cultivars available offer various color options, including many that are bicolored. Most are 4 to 6 feet tall, but there are also several dwarfs that will reach just 3 feet in height. The European Kalmia Society provides a full list of cultivars; these are some of the most popular choices:
- Kalmia latifolia 'Elf': This cultivar has white flowers and grows to just 3 feet tall and wide.
- K. latifolia 'Minuet': This cultivar flowers with white centers speckled with cherry red markings and surrounded by cherry-red margins. It reaches a mature size of just 3 feet tall and wide.
- K. latifolia 'Olympic Fire': This shrub red-pink buds that open to dark pink flowers; it grows 10 feet tall and wide.
- K. latifolia 'Peppermint': The flowers have red stripes that radiate from the flower center out to the edges of the petals, resembling hard peppermint candies. It grows 10 feet tall.
- K.'latifolia Firecracker': This cultivar tops out at 3 feet in height and has intense red-colored buds that open white then turn to light pink.
Mountain laurel is a slow-growing shrub that requires little pruning. Dead or broken branches can be removed anytime. Shaping pruning should be done in the spring, just after blooming is completed. Spent flower clusters should be deadheaded after the blooms fade.
Should your mountain laurel plants get too tall or gangly for your landscape design, cut them back almost to ground level to rejuvenate them. These tough shrubs can take a severe pruning when necessary. From stubs just a few inches above the ground, new foliage will arise, and your plants will mature into large shrubs once again in about ten years’ time.
Propagating Mountain Laurel
Mountain laurel is fairly easy to propagate by rooting stem cuttings, though it will take several months.
Take 6-inch cuttings from current-year growth and remove the leaves at the bottom of the cutting. Slice across the base of each cutting from the bottom to about 1 inch up. Dip the end of the cutting in rooting hormone, then plant it in potting soil. Put the potted cutting in a bright location and keep it moist and warm as roots develop and new leaf growth starts—this can take as much as six months.
Once the root system is well developed, your rooted cutting can be transplanted into the landscape.
Common Diseases and Pests
Mountain laurel is susceptible to leaf spots and blights. It is also prone to borers, scale, whiteflies, and lace bugs.
In heavy soils, mountain laurel can develop root rot, for which there is no cure. Affected plants will need to be removed.