Origin
Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. is a plant species belonging to the family Ericaceae. It is commonly known as bog laurel and can be found in the northern areas of North America including Canada, Alaska, and some parts of the United States.
Common Names
Bog laurel is the most common name of Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. Other names include swamp laurel, pale laurel, mountain laurel, bog kalmia, and lesser laurel.
Uses
The bog laurel plant has limited use in modern medicine, however, it has been used for traditional medicine among Native Americans. The leaves were ground into a poultice and applied topically for the treatment of sores and inflammation. The plant also has some ornamental value, and its attractive flowers can add a splash of color to a garden or landscape. However, it is important to note that the plant is toxic if ingested, and its use should be avoided for most purposes.
General Appearance
Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. is a deciduous shrub that can grow up to 2 feet tall. The plant has small, narrow, and elongated leaves that are dark green in color and glossy in texture. In late spring and early summer, the plant produces clusters of stunning pink or white flowers that are shaped like little cups. The flowers are highly fragrant and attract pollinators such as bees and butterflies. The plant thrives in wet and boggy conditions and is adapted to grow in acidic soils. Its hardiness and adaptability make it a popular choice for landscape designers seeking to create low-maintenance gardens in damp areas.
Light Requirements
Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. prefers partial shade to full sun exposure. The plant can tolerate full sun exposure, but it needs moist soil to thrive under such conditions. Therefore, it is advisable to grow K. polifolia var. rosmarinifolia in partial shade to protect the soil from drying out. Moreover, partial shade helps mitigate the plant's sensitivity to low temperatures by reducing the intensity of solar radiation which can cause damage.
Temperature Requirements
The optimal temperature range for Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. is between 55°F to 70°F. Avoid planting this species in regions where temperatures fall below 45°F, as the frost can damage the roots and reduce its general vitality. On the other hand, temperatures above 75°F can cause excessive transpiration, leading to desiccation and reduced growth rate. Therefore, the species is suitable for regions with moderate temperature ranges or grown under optimal temperatures through greenhouse farming.
Soil Requirements
Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. thrives in well-drained soils with high moisture retention capacity. The species prefers acidic soils that are rich in humus and organic matter. It should be grown in soils with a pH range of 4.5 to 5.5, as the plant cannot survive in soils with a pH level greater than 5.5. It is important to note that K. polifolia var. rosmarinifolia has low salt tolerance, and therefore, soils with a high salinity level should be avoided. When planting, amend the soil with organic matter to enhance its nutrient properties and water-holding capacity.
Cultivation Methods
Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd., commonly known as bog laurel, thrives in cool and moist climates. This plant can be cultivated either in containers or directly in the garden.
If planting directly in the garden, ensure that the area has rich, well-draining, and acidic soil. The ideal pH for Kalmia polifolia Wangenh. var. rosmarinifolia is between 4.5 to 6.0. Amend the soil with compost and peat moss to increase the acidity levels.
When it comes to sunlight, Kalmia polifolia Wangenh. var. rosmarinifolia prefers partial shade. However, it can tolerate full sunlight if the soil is constantly moist. When growing in a container, ensure that the pot has drainage holes and use a potting mix designed for acid-loving plants.
Watering Needs
Bog laurel needs to be watered frequently, especially during dry conditions. Keep the soil consistently moist and avoid overwatering, which can lead to root rot. Use rainwater or tap water that has been left to sit for 24 hours to remove chlorine.
Avoid applying water directly to the leaves and flowers, as it can cause fungal diseases. Instead, water at the base of the plant to ensure the soil is well-moistened.
Fertilization
Kalmia polifolia Wangenh. var. rosmarinifolia doesn't require heavy fertilization. Apply a slow-release, acid-loving fertilizer in spring following the manufacturer's instructions to avoid over-fertilization, which can damage the plant.
Alternatively, use organic matter like compost or aged manure to provide nutrients to the soil. Avoid using fresh manure as it can burn the plant roots.
Pruning
Pruning is not necessary for Kalmia polifolia Wangenh. var. rosmarinifolia, but it can help to shape the plant and promote healthy growth. Prune dead or damaged branches, and trim back new growth in early spring before flowering, if necessary. Avoid pruning after the flowering period as it can impact the next year's bloom.
It's essential to wear gloves when pruning Kalmia polifolia Wangenh. var. rosmarinifolia as the plant contains toxic compounds that can cause skin irritations.
Propagation of Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd.
Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd., also known as bog laurel or mountain laurel, can be propagated through several methods such as seed propagation, vegetative propagation, and cutting propagation.
Seed propagation
Kalmia polifolia can be propagated by seed, but it can be challenging. The seeds need a cold stratification period of around three months before planting. Cold stratification can be achieved by placing the seeds in moist sand or peat moss in a container and then storing them in a refrigerator for three months. After stratification, the seeds can be placed in a container with a planting mix and kept in a cool and moist area until germination.
Vegetative propagation
Vegetative propagation is a reliable method for propagating Kalmia polifolia. This method includes layering, division, and transplanting. Layering involves bending a branch down and burying part of it in the ground to allow it to root. After rooting, the new plant can be removed and transplanted. Division involves separating an established clump into smaller clumps, each containing roots and shoots. The separated segments can then be planted. Transplanting involves digging up a mature plant and dividing it into multiple smaller plants to be transplanted into new areas.
Cutting propagation
Propagation using cuttings can also be done with Kalmia polifolia. Softwood cuttings are taken from new growth in early to mid-summer and placed in a mixture of peat moss and sand. Semi-hardwood cuttings are taken in late summer and treated in the same way. The cuttings need to be kept moist and in a humid environment until they begin to root, usually around six to eight weeks. After rooting, the new plants can be transplanted.
Disease Management
Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. is generally resistant to most diseases, but it can still be susceptible to leaf spots, stem cankers, and root rots. These diseases can lead to discoloration of leaves, stem dieback, and plant death if not adequately managed.
Leaf Spots
Leaf spots are commonly caused by fungal pathogens such as Phyllosticta spp. and Septoria spp. Infected leaves develop small circular or irregular-shaped spots with gray or brown centers. Over time, the spots can blend together, leading to premature leaf drop. To manage leaf spots, remove infected leaves and ensure proper plant spacing to promote good air circulation around the plant.
Stem Cankers
Stem cankers are caused by fungal pathogens such as Botryosphaeria spp. and can affect the stems of Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. Infected stems develop sunken, brown spots that can girdle the plant, leading to wilting and death. To manage stem cankers, prune affected stems and apply a fungicide to the infected area.
Root Rots
Root rots are caused by fungal pathogens such as Phytophthora spp. and Pythium spp. Infected plants may show signs of stunting, yellowing, and wilting. The roots are often discolored, and the outer tissue can easily be pulled away from the inner tissue. To manage root rots, ensure proper drainage and do not overwater the plant. Fungicides can also be applied to the soil to help control the disease.
Pest Management
Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. is commonly attacked by pests such as lace bugs and spider mites. These pests can cause significant damage to the plant if not managed properly.
Lace Bugs
Lace bugs are small, winged insects that suck sap from the leaves of Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. Infested leaves develop a stippled or bleached appearance, and heavy infestations can cause premature leaf drop. To manage lace bugs, use insecticidal soap or a neem oil-based product to control the pest.
Spider Mites
Spider mites are common pests that feed on the leaves of Kalmia polifolia Wangenh. var. rosmarinifolia (Pursh) Rehd. Infested leaves develop a stippled appearance and may have webbing present. Heavy infestations can cause the plant to defoliate. To manage spider mites, use insecticidal soap or a neem oil-based product to control the pest.
