Azaleas & Rhododendrons: What’s The Difference?

purple rhodendron

Dandy Man Purple Rhododendron. Flower buds and full bloom. Photos: Proven Winners

These evergreen flowering shrubs get lumped together and you may wonder which is which. Both are members of the same plant Genus: Rhododendron. Plant taxonomists once put Azaleas in their own plant group, but later realized they were wrong about that. Taxonomists tend to do this a lot. So, all azaleas are rhododendrons, but not all rhododendrons are azaleas.
Here are the differences between what we commonly call Azaleas and Rhododendrons:

Bloomathon lavender azalea in bloom. Note the mulch layer to keep roots cool and moist.

Bloomathon lavender azalea in bloom. Note the mulch layer to keep roots cool and moist.

Azaleas

  • Smaller, duller leaves with a rougher texture
  • Mostly deciduous (loses leaves in winter if grown outside)
  • Smaller flowers, with 5 stamens
  • Small shrub, up to 8 feet (although unlikely in Toronto climate!)
  • Often sold as an indoor flowering potted plant.
  • Can be kept in pot year round, but give it a summer outdoors, and let it stay outside in fall in the cooler weather before bringing it back inside for the winter. This will help it set flower buds. Keep in a cool, very bright location. I’ve kept azaleas in pots blooming all winter in a west-facing, cool window. Don’t let it dry out!
  • Flower colours range from the whites and purples to yellow-orange and orange

Amy Cotta Rhododendron blossoms closeup. Note large flower size and number of stamens.

Amy Cotta Rhododendron blossoms closeup. Note large flower size and number of stamens.

Rhododendrons

  • Larger, shinier leaves with a “leathery’ appearance
  • Evergreen leaves
  • Larger flowers, very showy, with 10 or more stamens
  • Large shrub, can grow up to 80 feet high (again, unlikely in Toronto)

What They Have In Common:

  • Bloom in late spring. Flowers come in purple, lavender, white
  • Need acidic soil
  • Both grow in shade or dappled shade best, yet with plenty of water can take more sun
  • Don’t over-fertilize these shallow rooted plants, but when you fertilize azaleas and rhododendrons, do it after flowering.
  • Both benefit from a mulch around their roots, to regulate soil moisture and temperature.
  • Keep roots moist but not soggy.
  • Both can suffer from a yellowing of the leaf, called Chlorosis, defined by the Flower Expert, here:

chlorosis, characterized by yellowing of a leaf between dark green veins. Chlorosis can be caused by malnutrition caused by alkalinity of the soil, potassium deficiency, calcium deficiency, iron deficiency or magnesium deficiency. A combination of acidification with sulfur and iron supplements such as chelated iron or iron sulfate will usually treat this problem. Chlorosis can also be caused by nitrogen toxicity (caused by nitrate fertilizers)

 

 

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