Rhododendron catawbiense ‘Boursault’ is an evergreen shrub, celebrated for its robust nature and striking floral displays. Gardeners often select this variety due to its ability to thrive in various conditions, making it a reliable choice for many landscapes. Its vibrant blooms and consistent performance offer an appealing presence.
Understanding Rhododendron Catawbiense Boursault
‘Rhododendron catawbiense Boursault’ is a cultivar of the Catawba Rhododendron, native to the eastern United States. This broadleaf evergreen typically grows 6 to 10 feet tall and wide, though some can reach 15 feet. It is winter hardy in USDA Zones 4 through 8.
The plant features dark green, leathery leaves, 3 to 6 inches long. Its bloom period is late spring to early summer, typically June. Flowers emerge as deep purple buds, opening into lavender-pink to purple or blue-violet hues. These funnel-shaped blooms often display green, yellowish-brown, or reddish-brown markings in their throats, forming showy terminal clusters called trusses, each with 15 to 20 flowers. The dense, upright habit and uniform branches contribute to its attractive structure.
Planting and Growing Care
Site Selection
This shrub thrives in partial shade, particularly morning sun and afternoon shade, which protects it from intense midday heat. Protection from strong winter winds is also beneficial, as exposed locations can lead to desiccation. Good air circulation is important to prevent fungal issues, so avoid overly confined spaces.
Soil Preparation
‘Rhododendron catawbiense Boursault’ requires acidic, well-draining soil with a pH range of 4.5 to 5.5. Heavy clay soils can lead to root rot, so incorporating organic matter like peat moss, pine bark fines, or compost improves drainage and aeration. A soil test helps determine existing pH, allowing for appropriate amendments before planting.
Planting Technique
When planting, ensure the root ball is thoroughly moist; soaking it until air bubbles disappear is recommended. Dig a hole twice as wide as the root ball but only as deep, ensuring the plant’s crown remains at or slightly above the soil line. This shallow planting is crucial because rhododendrons have fibrous, shallow root systems that need access to oxygen. Backfill gently, avoiding compaction, and water thoroughly to settle the soil.
Watering
Consistent moisture is important, especially during dry periods and establishment. The soil should remain evenly moist but never waterlogged, as poor drainage can lead to root rot. Applying a 2-3 inch layer of organic mulch, such as pine bark or pine needles, helps retain moisture, regulate temperature, and suppress weeds.
Fertilization
‘Rhododendron catawbiense Boursault’ benefits from an acid-loving plant fertilizer, applied in early spring before new growth. Over-fertilization can harm the plant, so follow product instructions carefully. Organic options like cottonseed meal can also provide nutrients while maintaining soil acidity.
Pruning
This rhododendron generally requires minimal pruning. Any necessary pruning for shaping or removing dead or damaged branches should be done immediately after flowering. Pruning after new flower buds have set can reduce the following year’s bloom. Deadheading spent flower clusters encourages energy into stronger root systems and future blooms rather than seed production.
Common Problems and Solutions
Pests
Rhododendrons can be susceptible to pests like rhododendron borers and lace bugs. Borers tunnel into stems, causing wilting and dieback, managed by pruning affected branches or, in severe cases, insecticides. Lace bugs feed on leaf undersides, leading to a mottled appearance; horticultural oil or insecticidal soap controls them. Maintaining plant health helps deter infestations.
Diseases
Fungal diseases like root rot, leaf spot, and powdery mildew can affect ‘Rhododendron catawbiense Boursault’. Root rot occurs in poorly drained soils, causing wilting and yellowing leaves; improving drainage is the primary solution. Leaf spot manifests as dark spots on foliage, often from excessive moisture, mitigated by good air circulation and avoiding overhead watering. Powdery mildew appears as a white coating on leaves, treated with fungicides or by improving air circulation and reducing humidity.
Environmental Stress
Environmental factors can also cause issues. Chlorosis, yellowing leaves with green veins, indicates high soil pH, limiting iron absorption. Correct this by acidifying the soil with elemental sulfur or using fertilizers for acid-loving plants. Leaf scorch, brown or burnt leaf margins, results from excessive sun or wind, suggesting more sheltered planting. Bud blast, where flower buds fail to open and turn brown, can be caused by fungal infections or extreme cold; ensuring proper air circulation and winter protection helps prevent this.
Landscape Uses
‘Rhododendron catawbiense Boursault’ is a versatile evergreen shrub that enhances garden designs. Its moderate growth rate makes it suitable as a specimen plant, providing a focal point with its vibrant spring blooms. It also performs well in mass plantings, creating a continuous display of color and texture, effective in woodland gardens or along shrub borders.
Its dense, upright habit lends itself to informal hedges or foundation plantings, offering year-round privacy and structure. Companion plants thriving in similar acidic, well-draining conditions include hostas, ferns, azaleas, and hydrangeas, which complement its form and flower colors.