Rhododendrons and azaleas flower in just about every color, are often fragrant, and have beautiful, dark green foliage. Some species are evergreen; various species bloom anywhere from spring to autumn. There are hundreds of types to choose from.

Plant facts

  • Common name: Azalea; rhododendron
  • Botanical name: Rhododendron spp.
  • Zones: 3 to 11, depending on species
  • Size: To 50 feet tall and 30 feet wide, depending on species
  • From: Areas of Europe, Asia, and North America
  • Family: Ericaceae (heather family)


Growing conditions

  • Sun: Full sun to shade, depending on species.
  • Soil: Moist, acidic, well-drained soils are important. The plants don't grow well in alkaline or neutral soils.
  • Moisture: Water during times of drought.

Care

  • Mulch: A layer of mulch around the base of the plant will help keep weeds at bay. Mulch also helps conserve moisture and keeps soil temperatures consistent. Leave a 4-inch gap between the mulch and the plant stems.
  • Pruning: Except for deadheading, pruning usually isn't necessary. Improper pruning can ruin the plants' natural forms. If pruning becomes necessary, do so immediately after the plants finish blooming.
  • Fertilizer: In average soil, they don't require fertilization. Use an acid-reacting fertilizer, such as ammonium nitrate, to help plant health in alkaline soils.


Propagation

  • Seed: Sow seeds in a cold frame or a sheltered spot in the garden in autumn as soon as they are ripe. Don't cover the seeds-they need light to germinate. The medium you sow them in must be acidic. Note: Seedlings from named cultivars usually won't look like their parents.
  • Cuttings: Take cuttings in early or midsummer. Cuttings can take more than 4 months to root.
  • Layering: Bend one of the growing shoots toward the ground in early spring. Remove the leaves along a section of the stem, gently nick the stem in that area, then bury that section under several inches of soil and anchor the shoot down to the ground. The stem should root in about a year. After it roots, cut it from the mother plant.

Pests

  • Aphids: These small insects often appear in large numbers on new growth. Spray them off daily with a stream of water; they will not attack a plant after being knocked off. Use an insecticidal soap or neem-oil spray for severe infestations.
  • Borers: These insects bore tunnels beneath the bark, so you might see small holes with sawdust beneath them. To deter borers, encourage beneficial insects and use horticultural oil while the trees are dormant.
  • Leaf spot: In summer or autumn, the leaves develop yellow or brown spots, often with concentric rings that form a bull's-eye pattern. To deter leaf spot, prune the plant to allow good airflow and avoid wetting the foliage in afternoons and evenings
  • Powdery mildew: This disease appears in mid- to late summer. Affected leaves are covered with a grayish powder and eventually drop off. To deter the disease, prune the plant to allow good airflow and avoid wetting the foliage in afternoons and evenings.
  • Rust: Leaves develop spots and small masses of rusty-colored powder. Infected leaves die by the end of the season. To deter it, avoid getting the foliage wet; make sure there's good air circulation around plants.
  • Scale: Scale insects crawl up plant stems and cling to the plant. They appear as small, raised spots and are easy to overlook. To deter scales, encourage beneficial insects or apply insecticidal soap or horticultural oil.


Garden notes

  • Deadhead plants to keep them healthy.
  • These plants are divided into several categories:
  • Large-leaf rhododendrons
  • Small-leaf rhododendrons
  • Vireya rhododendrons
  • Deciduous azaleas
  • Evergreen azaleas


Selections

  • There are hundreds of selections with different sizes, bloom times, and colors. Choose carefully to ensure the best performance. Below are a few selections:
  • Rhododendron arborescens: Grows to 20 feet tall and wide with fragrant white or pink flowers in autumn. Zones 5 to 9. Native to areas of North America.
  • Rhododendron catawbiense: Grows to 10 feet tall and wide with reddish purple flowers and evergreen foliage. Zones 4 to 8. Native to areas of North America.
  • Rhododendron ‘Fragrantissimum': Evergreen that grows to 6 feet tall and wide with scented white flowers in early summer. Zones 9 to 10.
  • Rhododendron jasminiflorum: Topical vireya type. Grows to 3 feet tall and wide with evergreen foliage and sweetly scented white flowers in autumn and winter. Zone 10.
  • Rhododendron ‘PJM': Hybrid that grows to 4 feet tall and wide with evergreen foliage and pinkish flowers in spring. Zones 4 to 8.
  • Rhododendron yakushimanum: Grows to 3 feet tall and wide with evergreen foliage and pinkish white flowers in early summer. Zones 5 to 9.