• Date: 22nd January 2016
  • author: Lesley Eaton

The material upon which this discussion is based was created originally for use in connection with Short Courses in "Gardening with Azaleas & Rhododendrons" conducted by the Victorian Branch. The plants nominated are selected on their observed performance in Melbourne (the suburbs, rather than the more benign mountain environments nearby). There are enough similarities in climatic conditions in other locations in southeastern Australia that the nominations can be expected generally to be among the "hardier" of choices for the garden.

In the following lists, species are shown in italics, and hybrid plants in ordinary typeface.

Recommended for Growing
A short list of rhododendrons which have been found over time to do well in Melbourne gardens:

ASIATICS (cooler climate) rhododendrons

SPECIES: R.aberconwayii, R.arboreum, R.ciliicalyx, R.cubittii, R.davidsonianum, R.delavayii, R.irroratum, R.maddenii, R.ponticum, R.racemosum, R.yunnanense

HYBRIDS: Anne Teese*, Donvale Pearl*, Donvale Ruby*, Donvale Ruffles*, Florence Mann*, Wedding Gown*, Seta*, Loder's White, Bibiani, Mrs. EC. Stirling, Pink Delight, Sir Robert Peel, Unique, Fragrantissimum, Van Nes Sensation, Ivery's Scarlet, Hugh Koster, White Pearl, Jean Marie de Montague, Lamplighter

SPECIES: R.austrinum, R.luteum, R.occidentale, R.reticulatum
HYBRIDS: Cecile, Homebush, Gibraltar, Dr. Oesthoek

SPECIES: R.indicum, R.kaempferi, R.oldhamii, R.simsii,
HYBRIDS: Advent Bells, Kirin and Hinomayo , Alba Magnifica, Princess Maude, Apple Blossom, Red Ruffles, Blaaw's Pink, Red Wing, Coral Bells, Rose Queen,
Fielder's White, Splendens

SPECIES: R.aurigeranum, R. javanicum, R.laetum, R.lochiae, R.macgregoriae, R. zoelleri
HYBRIDS: Arthur's Choice, Liberty Bar, Bulolo Gold, Pink Seedling, Buttermilk, St. Valentine, Carillion Bells, Simbu Sunset, Coral Flare, Sunny

Asiatic rhododendrons which have indumentum under their leaves are well worth considering. The foliage has added decorative appeal (a feature to be enjoyed particularly in the non-flowering period of the year) and is long-lasting, and the indumentum provides added resistance to insect attack (especially against lacewing).

Many of the hybrids which were grown here in the early days (many still grown even today) were raised in England or Holland to suit conditions there. In general, their special requirements were that the plants should be cold-hardy and that they should flower late in the season to avoid their hard frosts. Here in Australia, our requirements in these two respects are quite different. We need plants which are heat-tolerant and preferably drought-tolerant, but which do not need to be particularly cold-hardy. Furthermore, we want plants which flower early in the season to avoid our hot weather with its accompanying dry winds which can ruin flowers in one day unless they are very well sheltered. A good deal of work has been done both by nurserymen and amateurs with these aims in mind, and there are now many hybrids available which suit our conditions quite well. Many can be seen in the "Australian Hybrids" section of the Rhododendron Garden at Olinda. A few appear in the above list - indicated by an asterisk * after the name. Our message to Australian gardeners is: don't overlook Australian hybrids!

These remarks so far refer to the Asiatic rhododendrons. So far as vireyas are concerned, many of the hybrids available in the trade here today have been raised in Australia, and naturally selections have been made with our requirements in mind. The fact that vireyas collectively flower throughout the year overcomes some of the problems discussed earlier regarding desirable flowering times, remembering, however, that as most are tropical (although typically not native to the hottest zones, but rather growing at relatively cooler altitudes), care needs to be taken even with our mild frosts.

Many of the small species and hybrids are available if you look for them, and should be considered seriously for use in the smaller suburban garden, or even for a town house balcony. You get more variety per square metre of garden with them.

As a general rule, the smaller the leaf size, the smaller the plant (or, at least, a plant which will flower while still quite small and which can then be kept down in size by judicious pruning after flowering).

Nature, of course, does not stick fast to such generalisations, and some specific knowledge is required for precision in predicting mature size of plants. This can be obtained from appropriate reference books, from experienced nursery growers, or from experienced amateur growers such as members of the Australian Rhododendron Society. Due to our different conditions, figures given in overseas books may not apply here.

As might be expected, some of the smaller rhododendrons are not as sturdy or as easy to grow as most of the larger ones. Here again, for appropriate information, experience from one source or another is required. A brief list of some easier-to-grow small plants of the 'Asiatic'-type rhododendrons follows:

SPECIES: R.moupinense, R.racemosum, R. cilipinense, R. chrysomanicum
HYBRIDS: Bowbells, Emasculum, Bric-a-brac, Florence Mann*, Chikor, Kimberley,
Ruby Hart, Saffron Queen, Elisabeth Hobbie, Seta

Position of your plant is very important and often not addressed as it can be a subtle thing. Your plant might thrive in one spot in your garden but not another. As a general statement your Rhododendron plant prefers an easterly aspect with morning sun and sheltered from afternoon sun, good air circulation and protection from strong dry winds but not in a cold dank place.

Rhododendrons & Azaleas

When you visit a flower display, nursery, garden centre or many of our chain stores during the rhododendron flowering time, you are confronted with a dazzling array of plants, which can at times be quite overwhelming. Therefore the question arises: "How do I choose some rhododendrons for my garden? "Your eyes will immediately lead you to either flower colours which are your personal favourites, or to something spectacular sometimes in a colour or shape which you would not normally expect to choose.
The questions you should then ask yourself are: "What size will this plant ultimately reach?" and "Will it grow to my satisfaction in my garden's conditions?" If your questions cannot be answered to your satisfaction by either the cultural notes attached to the plant or by the salesperson, do not hesitate to seek further information from either a specialist nursery, the ARS or from books in your local library.

Do remember that rhododendrons can grow from a few centimetres high, to great treelike dimensions. One word of warning - take the sizes on the plant labels as a guide only, as we have found that plants, if happy with Australian conditions, can exceed what has been stated. Remember, too, that size can vary depending on where in Australia you are growing your rhododendrons. Once again, personal preferences or what area is available in your garden will be your determining factors.
Do try a variety of growth habits to add interest. The bulk of the hardier rhododendrons have a good, bushy shape, but the leaves tend to be a matt green. Persevere though, as you can find some exciting alternatives.

There are some rhododendrons which have a light, willowy structure - ideal to use as a background for your borders, rock garden, or dwarf growing rhododendrons or azaleas. The soft mauve R. 'Emasculum' (often incorrectly labelled R. 'Praecox') is one willowy grower which immediately springs to mind, as is another early flowerer named 'PJM'. This plant has, as an added bonus, beautiful bronze foliage throughout the winter months - a most attractive feature!
Many rhododendrons can be used effectively as hedging or screening plants. The larger, upright growers with silver or cinnamon-backed leaves can make useful hedging subjects. As well as good, compact trusses of flowers, the interesting foliage allows these varieties to be attractive all year round, an important point to consider.

R. 'Pink Delight', an old cultivar with cinnamon-backed leaves, is one to seek, as is the brilliant red R. 'Ivery's Scarlet'. Don't be alarmed when seeing drooping leaves on these plants during winter. They are not showing signs of poor health, but are just adapting to the weather conditions. Some of the smaller cultivars can enjoy being clipped and made into small hedges. R. 'Blue Diamond' is an excellent example of this if you are fortunate enough to be able to provide the right conditions for 'the Blues'.!

Hedges could also be made using many of the azaleas. The Kurume types can be highly recommended for this purpose. Then to the other end of the scale, there are many rhododendrons which will fit perfectly into a rock garden setting.

Some of these small delights relish getting their roots under and between rocks, thus providing perfect conditions for their wellbeing. Within this rock garden group one can encounter quite a large range of flower shapes and sizes. In fact one often hears the comment 'Is that really a rhododendron?" The tiny thimble-shaped flowers of the species R. campylogynum come into this category, and some of its hybrids, such as R. 'Kim' and R. 'Canada', retain the unusual shape. Other dwarfs have small heads of flowers reminiscent of those of the daphnes, e.g. R. 'Sarled', and even have pungent foliage, another outstanding attribute. These dwarf growers are quite social plants and just love to be mass planted.

One must not forget the importance of foliage either, for after all, that is what is seen the whole year round. We have mentioned the silver and cinnamon-backed leaves earlier Often new growers are confused by this, and fear their plants are suffering from some terrible affliction. This coloured substance is known as indumentum and can be either soft and velvety or hard plastered. It can be generally said that the plants which have this lovely covering under their leaves seem to be able to stand up to attack of the azalea lace bug and other pests and diseases much better than some of the other softer, green-leafed cousins.

It cannot be stressed too much that the two most important needs for successful rhododendron culture are an acid soil and excellent drainage. It is always better to build up your garden beds than to dig holes in heavy soil and fill with compost etc. This can create a sump which can rot the roots. If you were to dig a 30cm hole and fill it with water, it should drain within a couple of hours. If your hole drains more slowly or stays full of water, you obviously have problems which need rectifying. There have been many articles in gardening magazines and on TV programs which give the experts' recipes for improving your drainage, and we are sure that we do not need to elaborate on the subject. We only wish to reiterate that good drainage is paramount for successful rhododendron culture.

After the establishment of good drainage and acid soil comes the question: What aspect do I give my rhododendron, and how much sun or shade?" Ideally, an easterly or south easterly aspect is the optimum. However, as this is not always possible, you must look for ways of providing a suitable microclimate. Although a good rule of thumb is "the smaller the leaf, the more sun, and vice versa", this has to be used with a good measure of common sense. The hot northerly and westerly winds in summer can play havoc with rhododendrons, so some shelter is obviously required. This could be in the form of a small deciduous tree or an evergreen whose roots are not greedy and would not compete with the rhododendron's food and water requirements. Here the choice is huge and only restricted by your own personal likes and dislikes. One word of warning however, silver birches are lovely trees but have very shallow; greedy root systems. Instead, maples, enkianthus, sorbuses, viburnums to name but a few, would be more appropriate.

Another alternative could be a light structure covered with shade cloth. This cloth is available in many colours and weights so it is possible to obtain the right choice for any situation. Once again, dealers will provide the expertise needed to make the right choice for each individual garden. With the exception of the vireya rhododendrons, frost is not the problem that growers in the northern hemisphere experience. However, shelter from trees, shrubs or shadecloth w~ lessen any damage which may occur if a heavier than usual frost is encountered. If your garden is in a frost-prone area, try selecting plants with a high hardiness rating. Many of the European hybrids come into this category, e.g. R. 'Tarantella' (a rich red), R. 'Bernstein' (biscuit yellow) or even some of the newer hybrids with R. yakushimanum in their parentage.

Companion plants can also help in producing that ideal micro-climate. Our nurseries provide a huge range of plants these days, so providing the cultural requirements are basically similar to those of rhododendrons, the sky's the limit.

Remember to try to choose shrubs which will either flower at a different time to rhododendrons or will provide colour in a different season, for rhododendrons have a solidity which needs enlivening by contrasting shrubs of lighter texture. Other trees and shrubs should shelter and protect rhododendrons from wind, temperature extremes and excessive sun. Don't forget though, that in too much shade rhododendrons will become long and lanky and flower only spasmodically, and can become targets for insect and fungal attack. Beware also of planting dwarf rhododendrons where falling leaves could smother the tiny plants.

Perennials and bulbs can make a lovely contrast. These could be planted in drifts between, or in front of your rhododendrons. Some suitable bulbs could be daffodils, scillas (Nuebells), snowdrops, snowflakes or liliums, to name but a few. Some perennials could include hostas, hellebores, primroses and other members of the primula family, woodland anemone or meconopsis. Ferns also associate perfectly with rhododendrons. Once again, personal preference plays an important role, for, after all, you are creating your own piece of paradise. Try not to let these companion plantings grow too close to your rhododendron roots, as rhododendrons detest too much disturbance around their shallow root systems.

Choosing a good specimen to take home to plant in your garden need not be an arduous task if these few pointers are considered. Firstly, look for a wellshaped bush with lush, unblemished foliage. Reject those with long, spindly growth and damaged, undersized or discoloured foliage. Beware of plants which look obviously pot-bound as they could be difficult to establish due to the absence of vigorous young roots.

Planting can be done year round, but probably the best time is in autumn, before the ground becomes too cold and wet, or in spring as the weather and the ground begin to warm up. We tend to favour the autumn as the roots are given a chance to develop into the surrounding soil before the winter sets in.
After working compost, a mild general fertiliser and drainage material into your ground or raised garden beds, it is time to start planting. Newly planted rhododendrons settle better into loose soil, so a little more effort before planting will certainly pay dividends. The soil-less potting mixes used in the present day, if allowed to dry out are almost impossible to wet again by any other method than soaking in a tub of water until the bubbles stop. It is important to do this as a rhododendron planted dry will not succeed. Make the hole at least twice the size of the plant's root ball, then place the well-soaked plant into it. Remember also to gently tease the roots so that they may quickly grow out into your own soil. Failure to do this can mean certain death to the plant as the roots tend to grow round and round in the potting mix and finally the plant succumbs to strangulation and starvation. Always water in your newly planted acquisitions to not only settle the roots, but to reduce any air pockets. We like to use a root stimulating formula at this time as the most important factor is to establish a good root system first, before worrying about producing flowers.

Many new plants will be bought either in flower or with flower buds. Nurserymen these days fertilise or add chemical retardants to induce early flowering to satisfy their customers. Do not despair then, if your rhododendron does not bud up as well in the following season. As long as the plant remains healthy looking it is probably just settling in and making a good root system.

When looking at plants to buy, don't automatically reject those devoid of flower buds. This may mean that the nurseryman is letting the plant develop at its own rate, or perhaps it is a variety that takes a few years to become mature enough to set flower buds. Many of the species rhododendrons come into this category as does the beautiful, old, early-flowering hybrid R. 'Cornubia'. Although patience is required, this is an excellent plant and is highly recommended, for when its red flowers appear, it is a sight to be seen.

Rhododendrons generally do not require large amounts of fertiliser. Good mulch, as it breaks down, can feed the plant sufficiently. However, some extra food can be used around the plants in early autumn and spring. Blood and bone or fertilisers produced specifically for rhododendrons are recommended. Osmocote® or similar slow release fertilisers, used according to the directions on the container can be used with good results. Azaleas and vireyas also respond well to liquid fertiliser, but care should be taken not to overdo the nitrogen content, as the soft, sappy growth it can encourage can be a perfect target for hungry insects or damage if an unexpected hot spell arrives.

Constant pruning of rhododendrons is not really necessary. The best way to develop good plants is to pinch out young buds when the plants are small as this can help develop a bushy plant. As with any plant, dead wood can be cut away at any time. Severe pruning, such as with very old plants can be achieved with a little care and a lot of patience as many old plants will have layered as well as grown tall. Many rhododendrons have latent growth buds along their stems which burst into life after pruning has taken place. Rhododendrons with smooth, peeling bark present a few more problems as sometimes after pruning regrowth is slow; or in some cases the cut stems will fail to shoot at all. We always remember being told by an astute nurseryman that the best way to prune most plants was to cut the flowers for the house, or to give them away to friends. Over the years we have taken his advice and can testify to the wisdom of his sentiments.

If your rhododendron is not looking happy in the position you have chosen for it, don't hesitate to move it. As a general rule, rhododendrons can be moved quite easily; just make sure the soil is moist around the plant, dig around the plant and carefully lift it into the new position. Water in with a root stimulant, mulch, and the plant should never look back.

Rhododendrons and azaleas lend themselves well to growing in containers, and today, with an abundance of beautiful pots and pans, you are only limited by your space and what size pot you can move around. With a little tender loving care, plants can live for many years or even indefinitely in containers. If you wish them to stay in containers indefinitely, you can lightly root prune them every year or so, refresh some of the potting mix, soak and feed. You will be pleasantly surprised at their longevity.
Azaleas are probably thought of first for growing in containers, but don't restrict yourself. Vireyas and some of the dwarf rhododendrons will grow in containers for many years as long as some basic requirements are met. Vireyas, often called 'tropical rhododendrons', are outstanding as potted plants. They do not require frequent repotting as they haven't a huge root system. An extra advantage is that they seem to flower periodically throughout the year, which certainly makes them good value. The dwarf rhododendrons prefer a wider than high container, commonly known as a pan, and, provided that they are kept out of the hot drying winds of summer, they will delight with masses of flowers for many a year. Some dwarf varieties to try in pots are: R. 'Patty Bee', R. 'Pink Silk', R. 'Dora Amateis', R. 'Snipe' or R. 'Ginny Gee'.

The first requirement is a container of suitable size for the chosen plant. Then a good quality, well drained potting mix should be purchased. Do not be tempted to overpot your plant as this can lead to disappointment and death of the plant. Once again, remember to water your newly potted plant, and place it in a sheltered place for a couple of weeks. As the plant becomes established, some fertiliser can be applied and the container placed in your selected position. We find it best to raise the pot off the ground as this allows the pot to drain more easily. Container plants can be brought inside for short periods whilst they are flowering, but care should be taken that they receive adequate water and light and are kept away from drying heating systems.

Lesley Eaton is a Past President of the national Society, and also a Past President of its Victorian Branch. Lesley now lives in Tasmania. This paper was written for use at Short Courses on "Gardening with Azaleas and Rhododendrons" presented by the Victorian Branch.