Rhododendron arborescens
Sweet Azalea, Smooth Azalea
Type Shrub, woody plant
Hardy range 6A to 8A
Height 4' to 6' / 1.20m to 1.80m
Spread 6' to 10' / 1.80m to 3.00m
Growth rate Slow
Form Oval and upright or erect
Exposure Partial shade or partial sun
Persistence Deciduous
Bloom Color Pink and white
Bloom Time Spring
The flowers are fragrant and very showy.
Environment
This plant tolerates some drought.
This plant will grow in dry soil.
Suitable soil is well-drained/loamy, sandy or clay.
The pH preference is an acidic to neutral (less than 6.8 to 7.2) soil.
Leaf Color Green
Fall Color No change in fall color
Culture Notes
Provide this plant with excellent drainage and organic soil. It is not salt tolerant or drought tolerant and does not do well to sweeping winter winds. Rhododendrons are ornamental, ericaceous, broad-leaved evergreens. They grow best in shade or partial shade. A south or southwest exposure increases the chance of winter injury to evergreen types when grown in northern climates.
Plant in an acid, moist, well-drained soil with a pH between 4.5 and 6.5. Flowers are said to be fragrant but I (Dr. Gilman) can smell nothing from this flower. This plant is considered mostly allergy free and causes little or no allergy problems in most people. Foliage from most members of this genus is considered poisonous when ingested.
Transplanting balled and burlapped or potted plants is most successful. The shallow root systems are easily injured by deep cultivation but benefit from mulching. Remove the old flower clusters as the flowers fade. Plants fail to absorb iron and have yellow leaves with green veins if the soil is not sufficiently acid. Finely ground sulphur can be added to the soil to increase acidity. Have the soil tested before planting in order to determine the pH. Apply a 2:1:1 N:P:K ratio fertilizer two or three times each year before and after bloom and perhaps again as plants enter dormancy - timing is not as critical as previously believed. Prevent winter burn in northern climates by avoiding exposed planting sites and by shading during winter.
Plants serve as butterfly nectar sources.
Planting and establishing shrubs
The most common cause of young plant failure is planting too deep. Plant the root ball no deeper than it was in the nursery. In most instances, the root flare zone (point where the top-most root in the root ball originates from the trunk) should be located just above the landscape soil surface. Sometimes plants come from the nursery with soil over the root flare. If there is soil over this area, scrape it off. The planting hole should be at least twice the width of the root ball, preferably wider. In all but exceptional circumstances where the soil is very poor, there is no need to incorporate anything into the backfill soil except the loosened soil that came out of the planting hole. Never place ANY soil over the root ball. If a row or grouping of plants is to be installed, excavating or loosening the soil in the entire bed and incorporating organic matter enhances root growth and establishment rate.
Weed suppression during establishment is essential. Apply a 3-inch thick layer of mulch around the plant to help control weed growth. Keep it at least 10 inches from the trunk. If you apply it over the root ball, apply only a one or two inch layer. This allows rainwater and air to easily enter the root ball and keeps the trunk dry. Placing mulch against the trunk or applying too thick a layer above the root ball can kill the plant by oxygen starvation, death of bark, stem and root diseases, prevention of hardening off for winter, vole and other rodent damage to the trunk, keeping soil too wet, or repelling water. Regular irrigation through the first growing season after planting encourages rapid root growth, which is essential for quick plant establishment.
