Kalmia Latifolia, known to most as mountain laurel, is an evergreen shrub that blooms during spring. The shrubs are made out of multiple stems, which intertwine and, when full of shiny, deep-green leaves, give out a beautiful aspect similar to rhododendrons.
I. Appearance and Characteristics
Kalmia latifolia, the mountain laurel, calico-bush, or spoonwood, is a species of flowering plant in the heath family Ericaceae, that is native to the eastern United States. Its range stretches from southern Maine south to northern Florida, and west to Indiana and Louisiana. Mountain laurel is the state flower of Connecticut and Pennsylvania. It is the namesake of Laurel County in Kentucky, the city of Laurel, Mississippi, and the Laurel Highlands in southwestern Pennsylvania.
The plant is naturally found on rocky slopes and mountainous forest areas. It thrives in acid soil, preferring a soil pH in the 4.5 to 5.5 range. The plant often grows in large thickets, covering great areas of forest floor. In the Appalachians, it can become a tree but is a shrub farther north. The species is a frequent component of oak-heath forests. In low, wet areas it grows densely, but in dry uplands it has a more sparse form. In the southern Appalachians, laurel thickets are referred to as “laurel hells” because it is nearly impossible to pass through one.
Kalmia latifolia is an evergreen shrub growing 3–9 m (9.8–29.5 ft) tall. The leaves are 3–12 cm long and 1–4 cm wide. The flowers are hexagonal, sometimes appearing to be pentagonal, ranging from light pink to white, and occur in clusters. There are several named cultivars that have darker shades of pink, red and maroon. It blooms in May and June. All parts of the plant are poisonous. The roots are fibrous and matted.
Kalmia latifolia has been marked as a pollinator plant, supporting and attracting butterflies and hummingbirds.
It is also notable for its unusual method of dispensing its pollen. As the flower grows, the filaments of its stamens are bent and brought into tension. When an insect lands on the flower, the tension is released, catapulting the pollen forcefully onto the insect. Experiments have shown the flower capable of flinging its pollen up to 15 cm. Physicist Lyman J. Briggs became fascinated with this phenomenon in the 1950s after his retirement from the National Bureau of Standards and conducted a series of experiments in order to explain it.
Toxicity
Mountain laurel is poisonous to several animals, including horses, goats, cattle, deer, monkeys, and humans, due to grayanotoxin and arbutin. The green parts of the plant, flowers, twigs, and pollen are all toxic, including food products made from them, such as toxic honey that may produce neurotoxic and gastrointestinal symptoms in humans eating more than a modest amount. Symptoms of toxicity begin to appear about 6 hours following ingestion. Symptoms include irregular or difficulty breathing, anorexia, repeated swallowing, profuse salivation, watering of the eyes and nose, cardiac distress, incoordination, depression, vomiting, frequent defecation, weakness, convulsions, paralysis, coma, and eventually death. Necropsy of animals who have died from spoonwood poisoning show gastrointestinal hemorrhage.
II. How to Grow and Care
Sunlight
Mountain laurel is highly prized because it performs well in part shade, but deep shade may reduce its flowering and cause leaf spots. It can tolerate full sun but the deep-green leaves may turn yellowish.
Temperature and Humidity
The shrub will do fine in warm weather 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.
Watering
A newly planted mountain laurel needs watering every three to four days for the first few weeks. Give it enough water to thoroughly moisten the soil without making it soggy. For the rest of the first growing season, water it about once a week. Ideally, the soil should always be moist, but once established this shrub has fairly good resistance to drought, as long as the soil does not dry out and overheat from too much sun exposure. In the absence of rain, water mountain laurel every two to three weeks in the spring and every week in the summer. Water it slowly and deeply until the first few inches of soil are moist to the touch.
Soil
These shrubs like cool, moist but well-drained, acidic soil (pH 5.0 to 5.5). Its natural habitat is wooded 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 berms or planters filled with a well-draining soil mix.
Fertilizing
Mountain laurel requires nutrient-rich soil to grow and produce flowers. They are acid-loving plants, so make sure to add acidic fertilizers. Fertilize just once, in spring or fall, to get the best results. More fertilization than that may lead to excessive foliage rather than flower growth.
Planting Instructions
Mountain laurel bushes should be planted from spring through summer when all dangers of frost have gone. Plant them in acidic, cold soil that is wet yet well-drained. The bushes should be spaced 4 to 6 feet apart; they like partial shade but can handle full sun. If at all possible, keep them away from windy locations.
These bushes should not be planted too deep in the ground. Make sure the top of the shrub – the place where the trunk meets the roots – isn’t buried. This situation should be avoided because your Mountain Laurel shrub will most likely perish as a result of decay on the buried crowns. When the shrubs are young, give them plenty of water and use wood chips or evergreen bark mulch to keep the soil wet and acidic.
If you are wondering where in the garden you should plant your laurel bushes, a woodland setting is the best way to go. They prefer to sit under tall trees, where bright sunlight is filtered by the tree foliage and does not burn them.
Pruning
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.
Propagation
Mountain laurel is fairly easy to propagate by rooting stem cuttings, though it will take up to six months. Growing mountain laurel from seed is possible but a finicky and lengthy process and not recommended. The seeds need to be collected at the right time before they develop their extremely hard seed coat, which can make the germination process take years. In addition, you will need to wait another ten years to see a seed-propagated mountain laurel reaching the stage where it blooms.
Here’s how to propagate mountain laurel from cuttings:
- In the late summer, or warmer climates in the fall, take six-inch cuttings from current-year growth using sharp pruners. Remove all the leaves from the lower half of the cuttings so the nodes are exposed—that’s where new roots will form.
- Slice across the base of each cutting from the bottom to about one inch up and dip the end of the cutting in rooting hormone.
- Fill four-inch plastic pots with a potting mix. With a pencil or a stick, poke a hole in the soil that is deep enough to fit the leafless portion of the cutting. Insert the cutting into the soil and press it down. Water it well until the soil is evenly moist.
- Place the pots in a bright location with indirect light, away from the hot sun. Keep them moist at all times and with a bottom heat of around 75 degrees F. In cooler climates, you’ll need to keep the pots indoors on a warming mat near a window with sufficient light.
- In a month or two, new roots will develop, and you should see new leaf growth. Once the root system is well developed—which is indicated by roots growing out of the pot’s drain holes—your rooted cuttings can be transplanted into the landscape. Make sure to harden off plants that were grown indoors. Gradually expose them to outdoor light during the day for about a week and return them indoors for the night, then leave them outdoors for a couple of days and nights before planting them.
Pests and Diseases
Mountain laurel is vulnerable to fungal diseases like leaf spot and blights. It’s also susceptible to insects like borers, whiteflies and lace bugs.
In heavy, clay soils, mountain laurel can get root rot. There’s no cure for root rot. The only solution is to dig up the plant, toss it in the compost pile and start over with a new mountain laurel.
III. Recommended Mountain Laurel Varieties
There are many types of mountain laurel, ranging from giants that reach 20 feet or higher to dwarfs that stay under 3 feet tall. Here are some of our favorites.
- ‘Elf’ is a dwarf mountain laurel with large, pink buds that turn almost white when they open. Elf grows to 3 feet tall and 4 feet wide.
- ‘Minuet’ is another dwarf variety. This one has light pink flowers with a bold red band. It grows 3 feet tall.
- ‘Olympic Fire’ grows to a sprawling 10 feet tall and wide. It has red-pink buds that open to dark pink flowers.
- ‘Snowdrift’ produces gorgeous white flowers on shiny, deep green foliage. Shrubs grow to an impressive 10 feet tall and 10 feet wide, making this a good choice for a spot where you want a tree-sized shrub.
IV. Uses and Benefits
- Medicinal uses
The Cherokee use the plant as an analgesic, placing an infusion of leaves on scratches made over location of the pain. They also rub the bristly edges of ten to twelve leaves over the skin for rheumatism, crush the leaves to rub brier scratches, use an infusion as a wash “to get rid of pests”, use a compound as a liniment, rub leaf ooze into the scratched skin of ball players to prevent cramps, and use a leaf salve for healing. They also use the wood for carving.
- Wood
Wood railing section made with mountain laurel branches
The wood of the mountain laurel is heavy and strong but brittle, with a close, straight grain. It has never been a viable commercial crop as it does not grow large enough, yet it is suitable for wreaths, furniture, bowls and other household items. It was used in the early 19th century in wooden-works clocks. Root burls were used for pipe bowls in place of imported briar burls unattainable during World War II. It can be used for handrails or guardrails.
- Ornamental uses
Mountain laurel (Kalmia latifolia) is a common evergreen shrub that offers plenty of ornamental appeal with its year-round glossy leaves and plentiful pink flowers. This shrub is well suited to mass plantings and border growth in informal and cottage gardens. Mountain laurel loves slight shade and grows well with similar species like Christmas fern and wild ginger.
Buy Plants
