Abundant azaleas
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Springtime is azalea time. Sure, some azaleas have been showing flowers since mid-winter, but the real abundance occurs once spring is well established. Rhododendrons, particularly evergreen azaleas, have long been my favourite shrubs, so I always look forward to this time of year.
Evergreen azaleas are not plants to be stingy with. If you have the room, use it, plant them in drifts where they can create solid blocks of colour and make a real impact. When planting, I prefer to use at least three of each cultivar as one plant takes too long to reach the size where it makes an impact. Also, the patchwork effect of a multitude of cultivars tends to be confusing and is usually less attractive than drift planting. When the plants get too large and start to grow into one another they can be transplanted and spaced further apart.
Beautiful as evergreen azaleas can be, I am well aware that many gardeners find them difficult to grow. As a former specialist commercial azalea grower, I have seen some tremendous plants and fantastic gardens. But I have also seen just about every mistake that it is possible to make and I can say without doubt that failures with azaleas are very seldom due to any failings on the part of the plants. Gardeners make mistakes, not plants.
Really, they're not that hard to succeed with, the big mistake is choosing the wrong plants. Not choosing azaleas over some other plant, rather choosing the wrong azaleas, because contrary to what appears to be the popular opinion they are not all the same.
Where they differ most and where it makes the greatest difference is hardiness. Although all evergreen azaleas will tolerate frost, there is a wide range of tolerance. Some may withstand only a few -2°C frosts before succumbing while others may emerge relatively unscathed from repeated -15°C freezes.
So how do you tell the difference and choose the right plants? Easy: know and understand the azalea groups. Like other large groups of plants: roses, camellias, chrysanthemums etc., evergreen azaleas are divided into several groups based primarily on their parentage.
These groups are widely recognised in horticultural circles except, However, visit any non-specialist nursery or garden centre and the chances are you will find azaleas labelled Indica and Kurume and possibly the odd Satsuki, but nothing labelled Kaempferi or Inter-Group even though the plants may be there. And the chances are the labelling isn't accurate anyway.
The information the nurseries need in order to get their labelling right and to keep their customers properly informed is readily available, though seldom used. You don't see nurseries labelling David Austin roses as Hybrid Teas just to keep things simple, but that's effectively what happens with evergreen azaleas when a Kaempferi is labelled as an Indica.
If I seem somewhat disillusioned that's because I am, but I don't blame the nurseries entirely, the customers have to share some of the responsibility, because if they don't ask the right questions there's little need for the staff to become knowledgeable enough to provide the right answers. Look at perennials: in recent years customers have become far better informed about them and now the nurseries provide a wide range of plant with accurate labels and promotional material where little existed previously. And it's not that evergreen azaleas are unpopular plants, a quick look at the main growers suggests that at least 250,000 are sold every year.
This article gives a brief summary of the main evergreen azalea types and what to expect from them, and it is important that you let your nursery know that you know what you're looking for. If it becomes apparent that the staff does not understand your needs or what you mean by azalea groups, then they probably do not know their plants very well. A harsh judgement, but true.
The main evergreen azalea groups are:
Indica
The Indica azaleas are the most tender and the most tempting. The thousands of hybrids in this group can trace their parentage back to Rhododendron simsii, a species from southern China, northern Burma and Taiwan. Rhododendron simsii can withstand occasional exposure to -6°C or lower, but repeated freezing will cause damage. Because of the influence of other species in their development, some Indica hybrids are reasonably hardy. Most, however, will be damaged by repeated exposure to -4°C or lower.
Indica azaleas are not strictly seasonal in their flowering and are easily forced into bloom. This has made them popular with florists and the house plant trade. Thousands of forced winter-blooming specimens are sold every year as house azaleas.
Belgian growers in the middle of the nineteenth century developed the Indica azalea as we know it today and the ensuing years have seen hundreds of hybrids developed with more appearing every year. Although the centre of European azalea development is now Holland, these European azaleas are still known as Belgian Indicas. Other commonly seen subdivisions of the Indica group include the Kerrigan, Rutherford and Southern Indicas.
This intensive breeding has led to Indicas having the showy, large, often multi-coloured, frilly double flowers and that is where the temptation factor comes in. Garden centres and nurseries rely heavily on impulse sales to shift Indica azaleas and the appeal of plants like 'Southern Aurora', 'Eureka', 'Gretel' or 'Leopold Astrid' in full bloom can be hard to resist. However, unless you live in a mild area where frosts are relatively light, irregular and neither early nor late, take care and be prepared for winter damage.
Kurume
These azaleas are named after the city of Kurume, which is located on the Island of Kyushu, Japan. They were introduced into Western gardens in 1918 and 1919 by the plant hunter E.H. Wilson and the Domoto brothers, nurserymen from San Francisco.
Kurumes are among the most immediately recognisable evergreen azaleas. This is primarily because of their flowers, which are small and often so abundant as to hide the foliage. The hose in hose flower, a form in which the sepals or stamens become petaloid and form a secondary corolla, is very common in Kurumes.
Kurume azaleas are usually quite hardy and most will tolerate -10°C with minimal damage. Once established it takes a very severe winter indeed to knock them back. For sheer weight of bloom combined with hardiness it's hard to beat the Kurumes, which explains why 'Kirin', the epitome of a Kurume, is one of the best known and most popular evergreen azaleas.
Kaempferi
Kaempferi azaleas, which are derived from Rhododendron kaempferi and Rhododendron poukhanense are the hardiest of the commonly available evergreen azaleas. They will tolerate at least -15°C if the wood is well-ripened in the autumn and will survive in most New Zealand gardens. In very cold areas most of the foliage may fall over winter, but the plants should survive.
Kaempferis have large, showy flowers and the best of them, such as 'Johanna', 'Lorna', 'Girard's Border Gem' and 'Vuyk's Scarlet' could easily be used in cold climates in place of the tender Indicas with no loss of flower power. These azaleas have foliage that often develops bright red and orange tones in the autumn and winter as an added bonus.
There are several different types of Kaempferi azaleas, the most common are the Kaempferi, Vuyk and Gable strains. Specialist nurseries may also have some of the very attractive Girard hybrids. Gardeners in the lower South Island and the central North Island should insist on Kaempferis for maximum hardiness.
Satsuki
Satsuki azaleas flower late, some may still be in bloom at New Year, and they have very distinctive flowers. Almost all of the cultivars have large single blooms that have a heavy, almost waxy texture. The flowers may be of one colour or irregularly striped, sectored or flecked with one or more secondary colours. One bush can show a range of flower patterns.
Most Satsukis are dwarf bushes with large, deep green leaves and in Japan they are grown as much for their form as their flowers. The very dwarf Gumpo azaleas, very popular for rockeries, are a form of Satsuki, but unlike the typical Satsuki they have small leaves.
Satsukis are beautiful plants and my personal favourites, but they are not popular with garden centres because they do not flower until after the main spring selling season. Their late flowering also means that they need to be shaded, otherwise the display will be very brief.
Inter-Group hybrids
As might be expected, the Inter-group hybrids are the result of interbreeding between the other groups. As a consequence these hybrids show a wide range of size, flower form and hardiness.
There are many different types of Inter-Group azaleas. The hardiest, plants like the Glenn Dale, Greenwood and Kehr hybrids, are as hardy as Kaempferis. Others, such as some of the Nuccio hybrids, are Indica-based and quite tender. When selecting Inter-group azaleas you really have to know the plants or have a good reference, or a knowledgeable supplier.
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Take the time to choose carefully and make sure that you get plants that are suited to your climate.
Having chosen the right plants, treat them properly. Prepare the soil well, as you would for any acid-soil woodlander and keep on top of the pests and diseases. The most common pests in the north are thrips, while further south it is leaf-miner/roller caterpillar. Both can be controlled with systemic insecticides or with fatty-acid sprays for the more organically inclined. In all cases good coverage is vital.
The only common disease is azalea leaf gall, which causes a thickening and distorting of the new leaves and occasionally the flower petals. This is really more of a cosmetic problem than a life-threatening one. Nevertheless it is unsightly. Fungicides containing thiophanate methyl offer the best control. They are best used as preventatives but if your plants do have infected leaves they need to be removed as the disease is soil-borne and failure to remove infected foliage can lead to a recurrence of leaf gall in following seasons.
Azaleas are beautiful and only become more appealing as they grow older. Making sure you choose the right varieties will ensure many years of heavy flowering with minimal disappointment.
Copyright Geoff Bryant
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