Perfect Companions: Kalmia
Courtenay, British Columbia, Canada
Reprinted from the North Island Chapter newsletter
We always seem to be looking for a companion plant for our rhododendrons, well here is one of the finest if not the finest, Kalmia latifolia and its cultivars. Botanists recognize seven species of laurel and group them into the genus Kalmia. All are native to North America. Mountain Laurel (Kalmia latifolia) is the best known species and is considered by some to be the most beautiful flowering shrub in North America.
Kalmia latifolia is a member of the Heath family and its needs are very similar to rhododendrons. They require well drained acid soil with a pH of 4 to 5.5. The soil should contain at least 50% humus so that it is light enough for the fine roots to penetrate.
When planting kalmia the top of the root ball should never be lower than the soil surface, where drainage and soil aeration are poor, the root ball should be set on the surface and filled around with soil consisting of 50% peat or other organic material.
When selecting a planting site several factors should be taken into consideration the more sun they receive the more dense their growth and the more prolific their flowering. On the other hand, partial shade from a high canopy of well spaced trees will extend the life of the flowers and prolong the blooming period.
The northern side of a building is one of the best planting sites for kalmia, here the plants are shaded in winter because of the low sun angle, daytime temperatures are moderate and the ground is subject to less freezing and thawing. In summer, they receive early morning and late afternoon sun but are shaded from the intense midday sun.
After planting, mulch with bark, pine needles or any other coarse organic material to conserve moisture and keep the soil cool, this mulch will also help to restrict the growth of weeds. Kalmia, because of their shallow root system should not be cultivated, weeds should be pulled or shaved off with a sharp hoe.
Fertilizing kalmia should be done sparingly, as they are not heavy feeders, light applications are recommended. Plants in good nutritious soils have a lustrous green to blue-green colour, good growth and leaf retention. Those in poor soils grow slowly, have poor colour and only retain the current year's foliage.
Removal of faded flowers is essential to consistent flowering, failure to do so will restrict new growth from forming, thus reducing bud set for the following year.
In the past, kalmia have always been grown from seed, as they are slow and difficult to propagate from cuttings. From these seeds have come some very interesting colour forms and shapes. Now with the aid of micro-propagation, some beautiful cultivars are becoming readily available. Some of the forms well worth having are: Kalmia latifolia 'Ostbo Red', 'Pink Charm', 'Olympic Fire', 'Pink Frost', 'Nipmuch', 'Goodrich', 'Shooting Star', 'Silver Dollar'.