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Written by davethetreecenters • May 08 In Search of Blue Rhododendrons

When a gardener’s mind turns to rhododendrons, they are most likely to picture a shrub with pink, or perhaps red, flowers. That’s because most species and varieties do indeed have flowers in that broad color range. But gardeners are a determined bunch, and the lure of something different is always there. That’s why, like the blue rose, the idea of a blue rhododendron has a special allure, and has captivated growers and breeders for a hundred years or more. Today we have varieties that come very close to true blue, and certainly fall well inside the rather forgiving boundaries that gardeners use to define ‘blue’. Some may disagree, and say, “Huh, that’s purple!”, and it’s true that if for you ‘blue’ is the sky, then these plants are not that, nor are they the blue of the best hydrangeas in acidic soil, or of tall blue delphiniums (plants today sadly hardly grown, and then often only as inferior varieties).

Most gardeners, though, are more forgiving, with elastic boundaries for their ‘blues’, and they will happily include the silver-greens of spruce, the obvious purples of lavender and catmint, and the softer ‘blues’ of some lilacs and even roses. Which opens us up to a good number of rhododendrons that certainly fall within those boundaries, and can easily and happily be seen as blue. It’s worth noting that we will never have a truly-blue rhododendron for a simple scientific reason. Among all the hundreds of species, not one of them has the necessary gene to make true-blue pigment, so no matter how hard we pray, we will have to rely on those purples and lilacs to get our ‘blue hit’ in the rhododendron garden.

Using Blue Rhododendrons in Your Garden

As we said, most rhododendrons fall into the pink and red range, and if you have a collection of them, you will have a gorgeous display for several weeks in spring. But if you aren’t careful, those big swathes of pink will get a bit ‘Barbie’ and maybe you want a more sophisticated look. That’s where these blues come in, and they do a fabulous job of cooling down a collection of the hottest reds or pinks, and also for adding range and depth to a grouping of strong purples.

Not only are these plants great in the typical woodland area where most of us grow our rhododendrons, they are also wonderful plants for a larger rock garden, especially in colder zones, where they will grow on slopes, in rocky pockets, and be right at home. In warmer zones you can also grow these plants in pots, where they thrive in a gritty, lime-free potting soil. Then you can place them on a table to truly enjoy their blooming, and put them in a less high-profile place until next year.

Blue Rhododendron Species

Most, but not all, of the blue rhododendrons are varieties produced by hybridizing older varieties and/or wild species, but some of the parent species of these hybrids are grown and relatively available, so let’s start with those.

Rhododendron impeditum – the Dwarf Purple Rhododendron

Rhododendron fastigiatum
credit: Steve Hootman, Co-Executive Director/Curator of the Rhododendron Species Botanical Garden, Federal Way, Washington

For reasons unknown, the best blue wild rhododendrons are found in the remote western mountains of China, a place of great romance in the folk-lore of gardening. Here it is, the low plants you can see clinging to the cliffs in western Yunnan, almost 12,000 feet above sea level. It is found growing with another, similar species, called Rhododendron fastigiatum. And here that species is, growing in a garden – if that isn’t blue enough for you, I’m sorry.

As you can see, these are low-growing plants, that are ideal for edging and grow especially well in rock gardens, thriving in full sun (if the soil is moist) in cooler zones. They are hardy in zone 5, and among the best evergreen rhododendrons for those colder zones. Their introduction via seeds is connected to two of the ‘big guns’ of Chinese plant collecting – the Englishman George Forrest in 1911 and the American Joseph Rock in 1924. Both struggled with war-lords, bandits and the climate to penetrate the remote mountain fastness that hid these plants. It is likely that plants sold in America come originally from seeds collected by Rock. Although usually given the prosaic name of Dwarf Purple, (obviously be someone who was pedantic about ‘blue’), personally I favor the more romantic alternative name of Cloudland Rhododendron, which has so much more charm to it.

Rhododendron fastigiatum

This sister species, already mentioned, is not so widely grown in it’s natural form, since it seems to be less hardy then the Cloudland Rhododendron. It has been used successfully, though, in hybrids with hardier species, giving us two terrific dwarf, purple-blue varieties, ‘Ramapo’ and ‘Purple Gem’.

Rhododendron ‘Ramapo’

The first is more widely grown, and is known to be hardy in zone 4, and it is likely that ‘Purple Gem’ is too. This means these are among the very few evergreen rhododendrons that can be grown in that zone, challenging for anything evergreen, and that makes them doubly delicious.

Rhododendron ‘Purple Gem’

These are perfect plants for edging in front of larger plants, or using in rock gardens or on slopes and banks. Of the two, ‘Ramapo’ is more acceptably ‘blue’, while it’s perhaps best to surrender and agree with the ‘purple’ in ‘Purple Gem’.

Blue Baron Rhododendron

The Cloudland Rhododendron shows up in another hybrid too, this time as part of an impressively-complex mix. Every gardener in the coldest zones has heard of – and likely grown – the hardiest evergreen rhododendron of them all, ‘PJM’. It was created by Ed Mezzitt, whose family owned Weston Nurseries in Massachusetts. Founded in 1923 the nursery became famous for the most cold-resistant of all rhododendrons, ‘PJM’ named by Ed after his father, Peter.

Ed didn’t stop there, though, and created a whole range of hybrids named after the nursery. Among these Weston Hybrids is ‘Blue Baron’, a a plant of complex lineage that includes Rhododendron impeditum among its ancestors. With this plant we are really getting into true-blue territory, and the vibrant blooms make quite a statement, on a bush that will in time reach 4 feet. In larger trusses than its Chinese parent, this is a plant for high-profile, more formal settings. Feast your eyes on this beauty, and weep because it isn’t in your garden.

Sadly not as hardy as the others we have mentioned, you will need to be in zone 6 at least to enjoy it, but otherwise it is as tough and as easy to grow as they are.

We could branch out at this point into other sources of blue, but it’s perhaps time to stop on a high point, and leave that for another time. So, don’t be blue, plant a blue rhododendron instead, make your neighbors green with envy and put yourself in the pink. (I’ll go now. . .)