Tree Talk: Thoroughbreds or mutts? Pondering rhododendrons

Provided to the MPT

There was a time, not long ago, when the horticultural world was abuzz with a snobby classism, not unlike the social registering of Edwardian Era Britain. Somehow rhododendrons took the brunt of it. The purists touted growing species rhododendrons (plants as nature made them, collected and cataloged from around the World). They scorned the gaudy newcomers, the hybrids, bred, as they would say, for big floppy flower clusters in popsicle colors, marketed to dazzle the unrefined? Fortunately, that silliness has passed. We’ve come to realize that hybridization, as is seen in the cross breeding of animals, often results in gorgeous and brilliant offspring.

All the same, the importance of pure species is not to be dismissed. There’s an intellectual side to knowing and growing them. The curious gardener takes pleasure in finding out where in the world the plant came from, how it might have been used in its indigenous habitat, and when it was introduced into cultivation. It is in knowing the species that the vastness of forms, sizes and leaf shapes can be seen, making the flowers secondary to the overall plant.

To understand that, go south on Interstate 5 to Federal Way and the Rhododendron Species Botanical Garden, 2525 South, 336th St., (253) 838-4646. Visit the website, With over 700 plants cultivated in this 22-acre garden, it is the world’s largest repository of species rhododendrons. This month the garden will be a symphony of bloom.

Most of the 1,024 known species of rhododendrons are native to eastern Asia and the Himalayas. But the United States has a few. Our Washington State Flower is Rhododendron macrophyllum. Rhododendron sinogrande, native to China and Tibet, has leathery, bright, dark green leaves that can measure 2 feet long and a foot wide. From Japan, R. yakusimanum is a compact shrub, to 3 feet tall with 3 inch leaves. Introduced into horticulture in 1760, R. ponticum is likely the most extensively cultivated rhododendron in Europe. It is native from the Iberian Peninsula to Western Asia. It naturalizes so easily that it is considered a pest in Ireland. Still, this rhododendron has had centuries of adoration, being the grandparent of many modern hybrids.      

Yes, the species are as fun to know as they are to grow. So why have rhododendrons been so extensively hybridized? For the most part: Flowers… big clusters of robust flowers in an assortment of vivid colors. For pop-your-eyes red, R. ‘Jean Marie de Montague’. For heavenly fragrance on large plants, look into the ‘Loderi’ hybrids. If you want a midseason bloomer filled with tight clusters of bloom in a blend of apricot, cream and pink, look for R. ‘Lem’s Cameo.’ Some breeders have developed plants for cold tolerance (an avocation that flourished in Finland). Others crossed species for interesting foliage, like R. ‘President Roosevelt’, most loved for its dark green leaves marked with golden yellow. If you’re looking for a handsome plant with dark burgundy leaves that will take full sun, heat, and cold (-25 F), R. ‘PJM’ is the classic.The offerings seem infinite. Even gardeners with huge estates complain that they have more on their wish list than they have room to grow.

Hybridization is an art, an arduous and long term process of isolating two species and cross pollinating them, then growing the seeds that germinate, waiting (often for years) and watching to see what the offspring is. If it’s a wonderful new plant, it is named, registered, propagated and put on the market. Many of the nursery people of the Pacific Northwes were and are, great hybridizers of rhododendrons and other plants. We all owe a debt of gratitude and affection to all of them for what they have given us and our gardens.

Shop for rhododendrons when they are in bloom. If you water them well through the summer, you can plant them when you buy them. Perfectly at home in our relatively cool, often overcast climate, they thrive in our loose, rich acid  soil. The ground they grow in needs to be constantly moist, albeit excellent drainage is essential to ward off root rot. Fertilize lightly with a 12-12-12 or the like, mid February, early April, late May and July. Water copiously in the dry season. On the hottest days it’s a good idea to give the plants a heavy misting early in the morning. A generous covering of compost atop the root zone is a good idea in November. 

So, species or hybrids? It really doesn’t matter. It’s what you like in any plant that counts. Rhododendrons are a bit like beloved dogs. Once you have one, whether it comes with a pedigree or came from the pound, you’re invested, you’re in love… thoroughbred or mutt.