Boursault Catawba Rhododendron

Hardy in USDA zones 4 to 8, the Boursault Catawba Rhododendron grows best in full to part sun with afternoon shade in hotter climates. Like all rhododendrons, it demands acidic, consistently moist but well-drained soil rich in organic matter; it will struggle in heavy clay or soggy ground.

Planting

1. Choose a spot with morning sun and afternoon shade and protection from harsh, drying winter wind.
2. Work plenty of compost or peat into the bed to create the loose, acidic, well-draining soil rhododendrons need; amend heavy clay generously or plant in a raised mound.
3. Dig a hole twice as wide as the root ball but no deeper, so the plant sits a touch high rather than too low.
4. Set the plant with the top of the root ball slightly above the surrounding soil line, since rhododendrons are shallow-rooted and resent being planted deep; backfill and water in well to settle the roots.
5. Spread a 2 to 3 inch layer of bark, pine straw, or other acidic mulch over the root zone, keeping it pulled back a few inches from the stems.

Care & maintenance

• Water. Keep the soil evenly moist, especially the first two seasons and during dry spells; the shallow roots dry out fast, but never let the plant sit in standing water.
• Feed. Apply an acid-forming fertilizer formulated for rhododendrons, azaleas, and camellias (a holly-tone type) in early spring after bloom; avoid heavy late-season feeding.
• Light. Full to part sun is ideal, with afternoon shade in warm zones to prevent leaf scorch; too much deep shade reduces flowering.
• Prune. This rhododendron blooms on old wood, so prune right after flowering finishes in spring. Snap off spent flower trusses just above the new growth buds, and shape lightly; pruning later in the season removes next year's flower buds.
• Mulch & winter care. Maintain an acidic mulch layer year-round to conserve moisture, moderate soil temperature, and protect the shallow roots; in exposed sites, shield young plants from drying winter wind.
• Pests & disease. Watch for lace bugs, root weevils, and spider mites, and guard against root rot by ensuring sharp drainage; yellowing leaves with green veins usually signal soil that is too alkaline and calls for added soil acidifier.

When does it bloom and how long?

The Boursault flowers in spring, opening large trusses of lavender-purple blooms that typically put on a show for a few weeks. As a spring bloomer it sets its flower buds the previous summer, so the buds you see in fall and winter are next spring's display.

Why isn't my rhododendron blooming?

The most common cause is pruning at the wrong time. Because this plant blooms on old wood, cutting it back in late summer, fall, or winter removes the buds that would have opened in spring. Too much deep shade, a hard late frost on swelling buds, or excessive high-nitrogen fertilizer (which pushes leaves at the expense of flowers) can also reduce bloom.

When and how should I prune it?

Prune right after the flowers fade in spring. Remove spent trusses by snapping them off just above the emerging growth buds, and make any shaping cuts at the same time. This gives the plant the rest of the season to set buds for the following spring.

Does it grow in sun or shade?

It performs best in full to part sun. In cooler zones it can take more sun, while in hotter regions it appreciates afternoon shade to prevent leaf scorch. The sweet spot for most gardens is morning sun with shelter from intense afternoon heat.

Is it deer resistant and good for pollinators?

Rhododendrons are generally considered deer resistant, as deer tend to avoid the leathery, toxic foliage, though no plant is entirely deer-proof when food is scarce. The spring trusses provide an early nectar source that draws bees and hummingbirds.

Why are the leaves turning yellow?

Yellowing leaves with green veins (chlorosis) usually mean the soil is too alkaline for this acid-loving shrub. Restore acidity with an iron-sulfur soil acidifier and an acid-forming fertilizer, and refresh acidic mulch such as pine straw. Uniform yellowing or wilting, by contrast, often points to poor drainage or root rot, so check that the plant is not sitting in soggy soil.