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Common Name:

Rhododendrons or Azaleas

Scientific Name:

Rhododendron spp.

Family Name:



Rhododendrons and Azaleas are America's favorite shrubs. They are valued for their flamboyant spring flowers and in some species handsome evergreen foliage. Newer selections may have extended flowering seasons. Heat and cold tolerance is extremely variable within and among species in the genus, but almost all require an acidic well drained soil with a steady moisture supply.

Plant Habit or Use:

Small shrub, medium shrub, large shrub, small tree, topiary


sun, partial sun, shade

Flower Color:

White, pink, yellow, red, orange, salmon, purple

Blooming Period:


Fruit Characteristics:

None ornamental woody capsule


variable, 2 ft to 10 ft, usually a rounded mound


2 ft to 10 ft

Earth–Kind® Index:

  • Heat Tolerance: High Heat Tolerance
  • Water Requirements: Medium Water Use
  • Soil Requirements: High Soil Requirements
  • Pest Tolerance: Medium Pest Resistance
  • Fertility Requirements: Low Fertility Requirements
Explanation of the Earth–Kind® Index breakdown

USDA Hardiness Zones:

4, 5, 6, 7, 8, 9, 10

Regions that intersect these hardiness zones:
Region A - Panhandle and High Plains Region B - North and Central Texas Region C - Northeast and East Texas Region D - West Texas Region E - Upper Rio Grande Region F - Hill Country and Central Coast Region G - Southeast Texas Region H - Rio Grande Valley
Click image for enlarged map of USDA Hardiness Zones

Additional Comments:

Cold hardiness varies from USDA zone 4 to only 8 or 9 for the tender types. Likewise, some species do not perfom well in zones warmer than 6 or 7. Avoid soil and foliar salt exposure to most genotypes. Rhododendrons are subject to desication in drying winds, particularly in regions where soils freeze.
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A Special Note about Cool Season Annuals

Cool season annuals typically are planted in the fall or early winter and flower in early spring under moderate temperatures. This group of plant materials includes: pansies, snapdragons, violas, dianthus, flowering cabbage/kale, etc. Because cool season annuals flower in the spring when conditions are mild, most have limited heat tolerance.

As a result cool season annuals do not receive a high Earth–Kind® index despite their outstanding landscape qualities.