Choosing Perfect Azaleas and Rhododendrons

Azaleas and Rhododendrons, with their magnificent flowers, are one of the best-loved sights of spring. Producing a blaze of color from early spring through the summer, and even into the fall, Azaleas and Rhododendrons are popular ornamental shrubs for gardens of all sizes. Evergreen or deciduous, they come in all shapes and sizes, from small, ground-hugging shrubs to large, tree-like specimens. Their flowers range from the tiny and delicate blossoms of floriferous dwarf shrubs to the huge clusters or ‘trusses’ of tall growing hybrids and species. Some are fragrant and others feature a wonderful foliage adding glorious fall color to the landscape. All are fascinating.

Azaleas and Rhododendrons are members of the genus Rhododendron, one of the largest genera in the plant world which includes over 900 species and over 20,000 named hybrids of Rhododendrons and Azaleas. Since finding the right plant can be daunting, here are some aspects to consider before buying a Rhododendron or Azalea.

Azaleas and Rhododendrons​ Hardiness

Azaleas and Rhododendrons must be suitable for the climate in which they will be planted. 

• Some varieties can tolerate severe winter conditions while others cannot.
  Many Azaleas and Rhododendrons are fully cold hardy, however, a few of them have frost-resistant flowers. Any flowers blooming before the last spring frost are susceptible to damage. Since the frost damage is generally caused when the early morning sun strikes the plants’ frozen tissues, you should site your Azalea or Rhododendron where both leaves and flowers are protected from the early morning sun, and where they will adapt slowly to the increasing temperatures of the day. Since frost flows downward, avoid planting them in low-lying spots known to be frost pockets.
  Amongst the varieties with frost-resistant flowers are Rhododendron lapponicum and Rhododendron hippophaeoides. There are also Rhododendron varieties that open their flowers in flushes over a long period, such as ‘Ptarmigan’ or ‘Christmas Cheer’. If one flush of flowers is damaged, another one will follow, and you will still be in a position to admire the new blossoms.
• Aside from spring frosts, winter winds are another source of danger. Azaleas and Rhododendrons may be harmed in winter by frozen grounds and drying winds or bright sun which will cause severe foliage desiccation. Protect their shallow roots with a mulch of oak leaves or pine needles and their foliage with woven material such as burlap screens. This will help in preventing bark-split (when the sap running in the stem is frozen and bursts the bark). 
• Here is a list of Azaleas and Rhododendrons that are exceptionally cold hardy and can withstand temperatures as low as -26ºF (-32ºC). They have all been recognized as proven performers and have received the Rhododendron of the Year Award from the American Rhododendron Society. Amongst them are some Iron-clads hybrids, which are regarded as the hardiest Rhododendrons and can tolerate open sites in sun (provided their roots remain moist).
• Heat tolerance is an issue that also needs to be considered. Most Rhododendron varieties exposed to the all-day sun are virtually guaranteed to die. In general, Rhododendrons in extreme climates benefit from filtered light and partial shade. However, there are available Rhododendron varieties that can stand the summer heat. 
  ‘Brown Eyes’ – pink with a golden-brown flare, 6 ft. (180 cm),
  ‘Janet Blair’ – very pale pinkish mauve with golden bronze rays, 6 ft. (180 cm)
  ‘Margaret Douglas’- pale pink with an orange-pink edge, 3 ft. (90 cm),
  ‘Mary Ann Egan’ – greenish-white edged with reddish-orange, 3 ft. (90 cm),
  ‘Mary Fleming’- cream flushed strong to light purplish pink, darker blotch in the throat, 2 ft. (60 cm),
  ‘Michelle Smith’- white with thickly dappled maroon flecks, 5 ft. (150 cm),
  ‘PJM Group’ – lilac purple to light violet, 4 ft. (120 cm),
  R. austrinum – in shades of yellow, gold, and orange. Very fragrant. 10 ft. (3 m)

When placing plants, always choose locations that mitigate extreme temperature changes, especially in spring and fall, and provide protection from drying summer or winter winds. 

Azaleas and Rhododendrons​ Size 

• Choose varieties that will grow on a scale appropriate for your landscape needs. Rhododendrons have no final size and can grow almost indefinitely. They range from dwarf, ground-hugging varieties which may reach 16 in. in 10 years (40 cm) to giant tree-like specimens as tall as 20 ft. or more (6 m). Both moisture and length of the growing season will have a serious impact on their growth rate. Some Rhododendrons will enjoy a fast growth rate (2 ft. per or 60 cm) while others will slowly grow less than 0.5 in. per year (1cm ). 
• If you choose plants that are the right size, to begin with, they are relatively maintenance-free. If not, Azaleas and Rhododendrons can be pruned to be kept small. Most varieties can be cut back if they get too large, except for some species with smooth bark which will not regenerate. All small-leaved Rhododendrons (Lepidote Rhododendrons) and deciduous or evergreen Azaleas can be cut back or pruned. 
• Plant habit is something that also needs to be considered. Some varieties enjoy a naturally rounded, ball-shaped habit, others are open and spreading as opposed to others with an upright growth habit. Tall growing rhododendrons make ideal screens or flowering hedges while medium-sized Rhododendrons and Azaleas are perfectly suited for beds and borders. Low-growing rhododendrons can be placed in front of other rhododendrons or used as foundation plantings. Dwarf Alpine Rhododendrons are effective in a rock garden, larger Rhododendrons are excellent for woodland gardens while compact hybrids are ideal in containers for shaded patios.

Azaleas and Rhododendrons Foliage

Rhododendrons often get chosen for their exquisite flowers, but their handsome foliage should not be overlooked. Rhododendrons have leaves in many shapes, colors, textures, and sizes that add striking interest and beauty to the garden all year-round year.  

• Some varieties have strikingly-colored new leaves that add dramatic beauty as the new leaves unfurl. Rhododendron keiskei, lutescens, decorum, or williamsianum would be good examples.
• Others are clothed with fine hair with hues ranging from silver to chestnut-bronze to gold, which can be seen when the leaves are ruffled by the wind. They include Rhododendron bureavii and pachysantum.
• Most deciduous Azaleas have glorious fall colors, extending the season of interest of your flowering shrubs. Here is a list of Azaleas and Rhododendrons with unusual charm in terms of fall color. Most of them have been recognized as proven performers and have received the Rhododendron of the Year Award of the American Rhododendron Society and/or the prestigious Award of Garden Merit of the Royal Horticultural Society. Some are delightfully fragrant, others are incredibly hardy and can withstand temperatures are low as -25°F (-32°C).
• Finally, many species have incredibly pretty peeling or colored bark such as Rhododendron thomsonii, faucium, or hodgsonii.

Azaleas and Rhododendrons Blooming Time

• Coveted for their spectacular blooms which come in a wide range of shapes and colors, Azaleas and Rhododendrons usually proudly display their colorful blooms for about three weeks, depending on the weather. According to the species, cultivar, and climate, Rhododendrons will bloom any time from late winter to late summer. In mild and maritime climates, their flowering season can extend up to 7 months of gorgeous blooms while in cold climates, it may be sharply reduced to 3 months. The very early flowering Rhododendrons may need frost protection while the late flowering varieties might require more shade to extend their bloom time. 

• Rhododendrons bloom best when they get good care. Their soil should be acidic, organic, moist, fertile, and well-drained. Each of these conditions is important to growing Azaleas and Rhododendrons successfully. 
• Choose a site with dappled shade in sheltered conditions. Avoid deep shade beneath other trees. Most Rhododendrons will tolerate a more open site if sheltered from cold, dry winds. Dwarf alpine species will tolerate full sun provided the soil is kept evenly moist. Avoid frost pockets and sites exposed to the early morning sun.
• For a long-lasting show of flowers, you may want to choose Rhododendrons and Azaleas that bloom at different seasons and enjoy the succession of their glorious blooms across the season. 

Azaleas and Rhododendrons​ Fragrance

There are many fragrant Rhododendron species and hybrids to pick from, some being so strongly perfumed that they will stop you as you walk past with their heady scent hanging in the air. 

Here is a list of fragrant Azaleas and Rhododendrons with staggering blossoms and reliable performances. Most of them have been recognized as proven performers and have received the Rhododendron of the Year Award of the American Rhododendron Society and/or the prestigious Award of Garden Merit of the Royal Horticultural Society. Some are tender and should be grown as patio plants or plants for the conservatory in cool winter areas, others are incredibly hardy and can withstand temperatures are low as -25°F (-32°C).

Be aware that fragrance fluctuates with temperature (on a warm day you will smell more perfume in the air), weather (strongest during damp mild weather), and time of day (most noticeable in the early morning or evening). Each of us has our own peculiarly individual perception of smell too!