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Rhododendron Choices for Small Gardens

May 23, 2020
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Rhododendrons are wonderful plants for many gardens.  John Good’s dwarf Rhododendron recommendations help you choose the best varieties for the smaller garden.

There are several hundred dwarf rhododendrons that are suitable for the smaller garden.

Those I have picked, all in my own garden, are small enough for most plots. None will grow to more than 1m high or wide in ten years. Those marked ‘AGM’ have received the Award of Garden Merit from the Royal Horticultural Society. This assures buyers that the plant in question is of outstanding merit, easy to cultivate, and readily available.

I will cover cultivation in detail in a following article. Suffice it to say here that dwarf rhododendrons, like all their kin, have an Achilles heel, they are lime (calcium) haters. They can, with difficulty, be grown on limy soils, requiring special like-free compost and lime-free watering.

But real success is only likely to be achieved in the long term on acid or neutral soils. The more organic matter that you provide, the better, and the soil should be kept moist at all times. While many rhododendrons grow best in woodland conditions, providing dappled shade, dwarf rhododendrons flower best in full sun.

Colour Palette in Dwarf Rhododendrons

Dwarf rhododendrons come in a dazzling rainbow array of colours, unmatched by any other group of dwarf shrubs.

They range from purest white, through palest yellows and pinks, stronger yellows and orange, dark pink and red, to true (and not so true) blues. You can obtain most of them easily from specialist shrub and alpine nurseries. A few may be more difficult to obtain, but well worth the chase.

Pink Rhododendron Choices

There are probably more pink dwarf rhododendrons than those of any other colour. So, its really a matter of seeing them in flower at a good nursery, or elsewhere, and choosing those you like best.

They generally blend well with most other colours, including the ‘blues’, which mostly contain some pink pigment.

Rhododendron ‘Kirin’

I am not generally a ‘fan’ of double flowers, but there are exceptions, and this is one of them.

The double, pale-pink, so-called hose-in-hose flowers, reliably cover the evergreen bush in late April. It thrives in full sun or partial shade, but flowers more profusely in the open.

This selection is more than a century old in cultivation. It is one of the best 50 evergreen azaleas selected by the famous plant collector,  Ernest Wilson, in Japan, known as ‘Wilson’s 50’. He introduced it to cultivation  with the others, in 1918, when they took the horticultural world by storm.

I am sometimes asked by gardeners, “what is the difference between azaleas and rhododendrons?”  The answer is, not much, chiefly botanical differences that need not concern most of us. In fact, azaleas are included as a division of the great Rhododendron ‘tribe’, so all azaleas belong to the Rhododendron genus, but not all Rhododendrons are azaleas.

However, most azaleas do look different from other rhododendrons.

Nearly all are deciduous, whereas most of the rest are evergreen, and azaleas generally have more numerous, smaller flowers. The confusion is compounded by the fact that azaleas for sale are sometimes labelled, say, ‘Azalea ‘Kirin’, sometimes (more correctly) as Rhododendron ‘Kirin’.

As most of those readily available are cultivars with ‘fancy’ names, your best bet is to look for the cultivar name of those you seek.

Rhododendron uniflorum var. imperator (syn. R. patulum)

A long name for a short plant! R. uniflorum var. imperator is among the first to flower here, generally at the end of March into early April.

It is also one of the prettiest, with plentiful blooms that are large in relation to the size of the plant. It is compact, slow-growing, a true alpine. Its mountain home is on steep banks, always above 3000 m altitude, in the Upper Irrawaddy river valley in Myanmar.

As so often with alpine plants, I am astonished that it is happy to exchange that distant, and very different homeland, for a mild, coastal garden in Wales.

Yellow Rhododendron Selections

Rhododendon ‘Sleeping Beauty’ and R. keiskei subsp. ozawae ‘Yaku Fairy’ AGM

These two little charmers are closely related. Rhododendron keiskei subsp. ozawae ‘Yaku Fairy’ is one of the parents of ‘Sleeping Beauty’.  The other parent is R. cinnabarinum subsp. xanthocodon, a much taller, yellow-flowered species which is too large to be included in this article.

The ‘mother, daughter’ relationship is clear in the photos, the chief difference is that  ‘Sleeping Beauty’ grows into a larger plant. It is also, as is often the case with hybrids, easier to grow than ‘Yaku Fairy’.  Both cover themselves in fulsome miniature trusses of pale yellow blossoms from late April to early May.

After twenty years, ‘Yaku Fairy’ is still only 25 cm high x 40 cm across, while ‘Sleeping Beauty’ has increased to almost twice those dimensions.

Rhododendron ‘Wren’ AGM

This easily available plant is yet another wonderful offspring of  R. keiskei ‘Yaku Fairy’, in this case crossed with R. ludlowii. The latter is quite challenging to grow.

This is not surprising, as its rocky home is at or above 4000 m in the Himalaya, on the border between N.E. India and Tibet.

Rhododendron ‘Wren’, however, has hybrid vigour aplenty and is one of the easiest, and most striking, yellow dwarf rhododendrons. Its flowers are larger, and more cup shaped than those of ‘Sleeping Beauty’ and ‘Yaku Fairy’. It is seen here growing on top of a raised bed, which seems to suit it, along with a number of others.

Rhododendron lowndesii

I cannot leave the ‘yellows’ without showing you one of my favourites among all plants, not just dwarf rhododendrons. Be warned, R. lowndesii is not easy to obtain, or to grow. But if you can manage it, you will surely be utterly beguiled.

Its elfin flowers, borne only 2cm above the dense, prostrate, creeping, evergreen foliage, are something  to behold. There may not be many, and you may need to get down on hands and knees to fully appreciate them, but its well worth the effort.

I grow the plant illustrated in permanently damp soil, in dappled shade, in a very rocky raised crevice bed. This is the nearest conditions I can provide to those in its homeland, on peaty banks and rock ledges, at around 4000 m altitude, in Nepal. It was named for Colonel Donald Lowndes (1899-1956), a retired Colonel in the Royal Garhwal Rifles and eminent plant hunter. He collected it there on a 1950 expedition.

Blue and Mauve Rhododendrons

No dwarf rhododendrons have pure blue flowers to rival those of, say, an alpine gentian. Most are some shade of mauve, or darker purplish blue, but they contribute greatly to the display. They look particularly well mixed with yellow and white varieties.

Rhododendron ‘Augfast’ (R. augustinii x fastigiatum)

This is one of the best blue dwarf rhododendrons in our garden, having grown to 75 cm high x 100 cm wide in 20 years. It is not surprising it is so good, as both its parents are first rate species.

Indeed, R. augustinii in full flower provides one of the highlights of the rhododendron season in many of our great British gardens, including Bodnant, near where I live.

Rhododendron fastigiatum (the other parent), is a true dwarf,  and probably in its best forms the nearest to a true blue. However, it is not as easy to grow as the hybrid, and in my experience is much more miserly in its flower production.

Rhododendron keleticum var. radicans

Another long name for a very short plant (radicans, in botanical Latin, means creeping). Strictly, it should be even longer as its full name is R. calostrotum subsp. keleticum var. radicans!

Of similar habit and stature to R. lowndesii, this is growing nearby in our garden. As you can see, it is certainly not ‘true, blue’, more a pinkish-mauve. This is a diminutive form, from high altitude, of a plant which in its ‘normal’ type makes a flat-topped bush about 25 cm high.

The species has a limited range in the wild in Tibet and Yunnan, just reaching into Myanmar. It comes from rather more densely vegetated habitats in the mountains than R. lowndesii, including meadows and bamboo thickets, from 3000-4000 m. In the garden it is one of the last to flower, often being at its best in late June, or even early July.

White Rhododendron Varieties

White rhododendrons are rare in the wild. But, selection by gardeners and rhododendron breeders, over many years, have produced a good range to choose from.

Quite a few have a pink tinge, but the flowers of those I have illustrated here are pure white when fully opened.

Rhododendron leucaspis

This entrancing species was introduced into cultivation in 1924 by the famed plant collector, Frank Kingdon Ward. He collected it in the Tsangpo Gorge, S.E. Tibet, at altitudes from 2500-3600 m.

For many people (including Kingdon Ward), this is their favourite dwarf rhododendron; it is certainly one of mine. Perhaps its most appealing feature is the chocolate coloured anthers, which contrast beautifully with the white petals. Its chief failings are that it is not easy to grow well, and that the flowers are easily damaged by frost which is not surprising, as they are produced in early March.

This is not, therefore, a plant for those who garden on frost-prone sites, unless protection can be provided. But it can be grown easily and well in a pot, or other container, where it can be protected from the vagaries of the late winter weather under glass.

There are some very good hybrids of  R. leucaspis. I have ‘Snow Lady’ and ‘Ptarmigan’. Both are as early flowering as R. leucaspis, with slightly more frost hardy flowers, and are easier to grow. But the chocolate coloured anthers are neither as dark, or as large and imposing as those of their illustrious parent.

Rhododendron ‘Sarled’ AGM

The flowers of this plant, and the group of dwarf rhododendrons to which it belongs, are quite unlike those of the other species and cultivars described so far. They are popularly known as daphne flowered rhododendrons, for obvious reasons.

Rhododendron ‘Sarled’ is easy to grow, long-lived, and the flowers last longer than those of most dwarf rhododendrons; up to 4 weeks. They open palest pink, but soon age to a clear, bright white.

While the flowers are scentless, the foliage has a strong resinous odour which will make itself apparent if you happen to brush it when passing, or weeding nearby.

The smell tells you immediately that this is a ‘lepidote’ (meaning scaly) rhododendron. All other rhododendrons (most larger species and some dwarfs) are in the ‘elepidote’ group.

The scales of the lepidote rhododendrons, that produce the resinous oil, may cover the whole plant or be mainly or exclusively limited to the under-surfaces of the leaves.  They are typically hardly noticeable without close inspection, preferably with a hand lens. Technically, they are modified glandular hairs.

Rhododendron ‘Egret’ AGM

The bell-shaped, waxy flowers of this hybrid owe these attractive characteristics to the seed parent, R. campylogynum.

This is a variable, slow-growing species that can be had in a range of colours from white, through various shades of pink, to dark claret. It is a very good parent, having been used to produce a range of hybrids in this colour range and more.

But the pure white bells of ‘Egret’, with their dark anthers and protruding, clapper-like styles (female reproductive organs), take some beating.

Red Rhododendrons

There are relatively few, good, red-flowered dwarf rhododendrons, but the best are outstanding.

One piece of advice is to ensure that, particularly those with very dark red flowers, are placed in a situation that is well lit at the time of flowering. Otherwise they can look too dark and loose their impact.

Rhododendron ‘Scarlet Wonder’ AGM

This is a reliable, strong, bright red, that will eventually make a bush twice as wide as high. It is widely available.

Rhododendron camtschaticum

This is a rare, miniature, creeping rhododendron from the vast boglands (muskeg in N. America) of the Kamchatka Peninsula, Japan and Alaska. That tells you that it must never be allowed to dry out at the root.

It is unusual in being deciduous, even though it is not in the azalea section of rhododendron. It is a uniform plant in all but flower colour, which ranges from a rather wishy-washy, pale pink, to the strong, vibrant red illustrated. So you need to know what you are buying.

There is an even rarer, pure white albino in cultivation, but I have never managed to acquire it… yet!

Rhododendron nakaharae ‘Mariko’

This is one of several selections of this creeping, evergreen species, which is only found on one Taiwanese mountain, at elevations between 2000-2500 m. It is particularly valuable in the garden for its dwarf, tidy habit.

Also, because it does not produce its bright orange-red flowers until June-July, long after most other dwarf rhododendrons are finished. It is more tolerant of dry soils than many others, and grows well in fairly deep shade beneath trees.

Enjoy your Dwarf Rhododendrons!

I hope that this small personal selection of dwarf rhododendrons will whet your appetite to try some in your garden.

They will be with you a long time, 25 year old plants in good vigour and flowering freely are not unusual. So take some time in choosing those that you like best. And don’t forget to top-dress them occasionally with a good ericaceous compost, mixed with fine sand, working it well down into the plants.

An occasional watering with specially prepared rhododendron (ericaceous) liquid feed, available from good garden centres, will also help to keep your plants in good condition.

Image of John Good John Good