Rhododendron williamsianum

Rhododendron williamsianum, introduced to horticulturists of the western world in 1908 by Ernest "Chinese" Wilson is at once one of the most recognizable and one of the most enchanting rhododendrons. Its unique combination of almost orbicular, mid-green leaves, spreading and somewhat rounded or dome-shaped habit, and disproportionately large, candy-pink, campanulate flowers make it easy to recognize and well-adapted to gardens both large and small. Its densely mounded shape often has a somewhat brooding appearance, a bit like having a very large toadstool in the garden...but its solid presence makes a good anchor to a plant grouping, and can provide an effective screen, if needed.

Although never thought of as a large rhododendron, it can in time become quite massive, spreading up and out in large billowy curves that are certainly beyond the reach of vertically-challenged gardeners.

R. williamsianum flower
Photo by Chris Klapwijk

It was a species that has so captured the imagination of rhododendron fanciers that a veritable frenzy of hybridizing ensured. After all, there were so many positive characteristics to try to attach to other rhododendrons: small, tidy, glabrous leaves, with lovely bronze new growth, well-shaped, pretty pink blossoms that were large in relation to the leaf size, and a spreading compact habit that keep the blossom down where people could easily admire them.

Looking through Salley and Greer's book Rhododendron Hybrids, I gave up counting at the end of the C's, having reached something over 55 hybrids. Each decade seemed to bring on a new wave of williamsianum crosses:

  • Rothschild in the early 30s, including the iconic hybrid 'Bow Bells'.
  • Lord Aberconway in the late 30s and early 40s, with a whole series of hybrids beginning with "A" ('Adrastia', 'Adrean', 'Amata') as if he were trying to get in first in the Yellow Pages, but also developing the wonderful 'Cowslip', a williamsianum x wardii cross.
  • Hobbie in the mid 40s, with his 'Gartendirektor(s) 'Glocker' and 'Reiger'
  • all the way up to Weldon Delp and Hans Hachman's more recent hybrids.
  • Even J. C . Williams of Caerhays Castle used this namesake rhodo in his inspired 'Hummingbird' cross with R. haematodes.

R. williamsianum is truly endemic to Sichuan, China, being found only there, and even within that province its distribution is very limited. However, it is now in constant and widespread production and cultivation all over the world.

Lepidote Rhododendrons

Rhododendron enthusiasts are often asked what they mean when they refer to a rhododendron as a "lepidote". The confusion is compounded when one sees quite a bit of space devoted to lepidotes in flower shows.

A nurseryman may tell you casually that it refers to the small-leaved evergreen rhododendron. This can be used as a generality...but not as a hard and fast rule...as there is a fair amount of overlap between lepidotes and the "large-leaved" elepidotes.

Real traits that make it a useful distinction is lepidote rhododendrons have scales on the underside of the leaf which protect the plant's stomata (leaf pores) through which oxygen, carbon dioxide, and water vapor pass. The scales evolved originally to regulate moisture, to help keep water in the cells in dry times, and help shed it in times of surfeit . This allowed plants evolving in the tropics to live in the quick-drying forest duff on the very thin soils of the tropics, or even epiphytically on rocks or tree trunks. Turn a leaf of the lepidote over and look for the tiny scales; some are big enough to see with the naked eye, but a hand lens will reveal a world of otherwise hidden detail. Elepidotes, on the other hand, are without scales to cover their stomata.

But winter brings many of the same demands as the tropics on a plant...encasing it in wet snow or desiccating it with cold dry winds, and the scales evolved to become adept at dealing with harsh winters as well. As a result, lepidote rhododendrons have adopted and spread to nearly all environments, from tropical jungles and Siberian woodlands to mountain meadows and alpine tundra. Because of this wide tolerance of soils, temperatures and exposures, they are especially useful to gardeners in the Northeast United States. Other adaptations, such as fast regrowth after predation from grazing animals, and early bloom to deal with short growing seasons in cold climates, give us a plant that is easily pruned to shape and early to give the gardener a boost after a long winter.

Most lepidotes have axillary buds...extra flower buds under the terminal flower bud or along the branch...and in bloom often smother the foliage until all you can see are the flowers. Lepidote species range from tiny creeping alpines suitable for the rock garden to tall forest and meadow plants for woodland wildflower gardens and formal borders.

Best of all, the hybrids developed by plant breeders bring hybrid vigor to the party, giving us a huge range of plants, among them some of the easiest and the hardiest rhododendrons to grow in cold climates. A commonly grown lepidote cultivar is "Rhododendron 'PJM', which was hybridized by the Mezitts, and is now grown and admired all around the gardening world.

The large-leaved fancy varieties of rhododendrons may get all the big press...but for vigor, hardiness, adaptability, easy of culture, and sheer traffic-stopping, eye-popping show of flowers in the spring...my money is on the lepidotes!

 From the Massachusetts Chapter Newsletter, September 2006.

Growing Rhododendrons From Seed

Rhododendrons and azaleas are easily grown from seed. Unless the parent plants are species from isolated areas, the resulting seedlings will exhibit much variability. Unless you are interested in hybridizing and selecting new cultivars, use of seeds as a means of propagation should thus be limited to species plants. Even then some physical differences will be evident.


  1. Obtain clean seeds.
  2. Prepare a sterile container at least three inches deep, with bottom drainage; size depending on how many seeds you wish to plant.
  3. Fill the container to within ½ inch of the top with a mixture of 40% perlite and 60% fine sphagnum peat moss. This mixture should be moist...but not wet.
  4. Level and firm the surface of the mix.
  5. To control fungal disease, spray the soil surface with fungicide Captan. Read and follow product instructions.
  6. Sprinkle seeds thinly on the surface...do not water again.
  7. Put plastic or glass over the container to make it moisture tight.
  8. Place in a warm dimly lit area until seeds germinate.
  9. Put under fluorescent light for 18 hours a day at 70-75°F.
  10. Anytime after true leaves have formed, harden the seedlings off by gradually opening the cover over the period of at least one week. Water carefully as needed to keep moist. Watering through drainage holes in the bottom is safest.
  11. Transplant when ½ to 1 inch tall to flats using 50% sphagnum peat and 50% perlite. Lift under the roots and handle by a leaf. Plant at same depth. Water to settle in.
  12. Water to keep moist, but not wet. Fertilize with azalea food or other acid fertilizer once a month using ½ half strength. Always water at least once between fertilizer applications. To slow growth and harden off, stop fertilizing and water less frequently.
  13. Transplant when seedlings become crowded.

Keep the growing area clean to prevent damping off, water properly, and...success is almost assured!

Black-flowered Rhododendron

Looking for a rhododendron with black-looking flowers? Rhododendron 'Black Widow' is causing quite a stir among collectors as its very dark maroon flowers appear to be almost black. Also, to add even more interest, this interesting hybrid has white stamens which stand out against the black, wavy-edged petals. Up to 21 flowers are held in ball-shaped flower trusses. Bloom-time is typically May in North America.

Photo by Harold Greer

This unique cultivar was created by Roy Thompson of Waldport, Oregon by first crossing the dark purple, flowered rhododendron 'Frank Galsworthy' with 'Leo', which has a rich, dark-red flower. He called this hybrid 'Gal-Leo'. He then crossed this plant with the maroon-flowered rhododendron 'Warlock'. In order to increase his chances of finding a black flower, he planted out several hundred seedlings of this cross. The best one of the lot Roy named 'Black Widow'

The plant's bright green foliage is 6.5" long, elliptic in shape, ribbed and shiny on top. It has an upright and spreading growth habit, and it grows to a typical height of 3 feet in 10 years. The plant is cold hardy to at least -5°F (-21°C).

Consider having this wonderful rhododendron cultivar in your garden.

Winter Protection For Rhododendrons

If you haven't planted your rhododendrons in a protected location, you may have to consider providing them with some winter protection! Rhododendrons, particularly large-leafed forms, are sensitive to winter sun as well as winter winds, and if not protected properly, you may have serious damage or lose the plant by spring.

Damage to plants is likely to happened if the plant did not receive ample moisture before in the Fall. During the winter, drying winds and frozen ground deprives plants of their natural moisture intake. The exposed portions of the leaf...usually the central portion when the leaf was curled...may become brown. This may also appear on the edges of some leaves.

To prevent scorch, plants should be well watered in November, especially if rainfall has been sparse; protected from drying winds; mulched well, and given some shade. New plant growth may not have a sufficient amount of time to become woodsy and harden off for the winter. Also, flower buds are the least cold hardy part of the plant.

Rhododendrons, boxwood, azaleas, hollies, and laurel will benefit from an application of an anti-desiccant, such as Wilt-Pruf. Read and follow all instructions. Spraying should occur in late Fall when temperatures are near 40 degrees F. Most anti-desiccants are composed of a "waxy" substance that can break down during winter's thaws necessitating a reapplication.

If you do not get a chance to apply an anti-desiccant, you may want to provide a wind-shield, such as burlap to these shrubs as well as some mulch protection around the base of the shrub. Young plants can be enclosed with chicken wire or dog fencing, and packed loosely with oak leaves. Remove the protection in the spring as buds start expanding. Mature plants can be mulched with several inches of wood chips at the base.

Evergreen boughs can be leaned or tied against plants to limit winter injury. A teepee-like structure constructed with three or four evergreen trees or branches with their points forced into the ground and tips tied together provides adequate protection...or use a burlap covering around individual plants. Snow fencing alone or with a polyethylene plastic sheeting attached to it also gives effective wind protection. Cover the plants just before freeze up in the Fall and uncover after all the frost is out of the ground in the spring.

Weigela...a companion plant

Once the main splash of rhododendrons is over, there is a charming group of plants that fills the color gaps in our landscapes quite nicely. Named after a German botanist, Christian von Weigel, Weigelas are deciduous shrubs of open woodland areas in parts of Asia which have a multitude of foliage and flower features.

Most of our available varieties are selections or hybrids of two species: W. florida and W. praecox, although the wild forms are rarely offered. The blooms, in May and June, are tubular, in small clusters along older stems, often with nicely contrasting stamens. In blossom, they attract hummingbirds by the flock.

The "in" thing these days among plant introducers is purple leaves, starting back with 'Foiliis Purpureis' ('Java Red')...on to 'Victoria', then 'Wine and Roses' ('Alexandra'), 'Ruby Queen', and now 'Midnight Wine'! The color is getting darker, and the plant habit is getting smaller...what's next...a black groundcover Weigela? Attractive and useful plants nevertheless...most of them have pink to bright pink blooms.

The 'Dance Series', developed by Agriculture Canada, have all been selected for very compact habits, extra hardiness, and richly colored blooms. Foliage variations are from green to burgundy, with deep pink or red blooms. Look for 'Tango', 'Polka', 'Samba', 'Rumba' and 'Minuet'.

Gold-leafed forms are a bit more finicky...they need partial shade to avoid foliage burn but too much shade makes them go green so it's a fine line. 'Looymansii Aurea' has pale pink blooms, while the newer 'Briant Rubidor' (aka 'Olympiade' or 'Golden Ruby') has dark ruby flowers that offer a striking contrast. Variegated leaves, with cream to light yellow margins, occur in both species, and have pink flowers. The variegated areas take on rich pink to red tones in fall, for extra punch.

White-flowered forms are available as 'Bristol Snowflake', 'Candida', 'Mont Blanc', and others...but I must admit I don't really care for them...although 'Mont Blanc' is highly rated. Possibly I just haven't seen one at the right stage or in the right setting. A new introduction, 'Carnaval', has blooms of white and two shades of pink all at once on the same plant. That's kind of neat! For deep red, the old 'Bristol Ruby' and 'Eva Rathke', although good and reliable, have been superseded by newer, tidier, non-fading varieties like 'Red Prince', 'Lucifer', and the even smaller 'Nain Rouge'.

Weigelas grow easily in any well-drained moderate soil...and old bloomed-out stems can be cut to the ground to allow new ones to take their place. Trim right after blossoming in the early summer to keep leggy branches in order, and to give time for the wood to ripen and set bloom for next year. Some varieties will bloom off and on throughout the summer, and other appear in early summer and again in early fall.

Two unusual species, W. middendorffiana and W. maximowiczii, have light yellow flowers in late spring...most "un-weigela-like", but truthfully I have not seen either offered for sale locally. Good for you if you can fine one!

Look around in the plant centers when you've gotten all your beddings settled and your rhodos are on the wane...and you'll find one of these to be a delightful addition to your garden...big or small!

Happy Planting!