On the suitability of satsuki azalea cultivars for bonsai

When growing azaleas as bonsai, the characteristics of the cultivar can affect bonsai decisions and outcomes. With respect to bonsai of species other than azaleas, it is generally the wild forms that are preferred over the cultivars. Cltivated forms of pine and juniper usually have traits that make them more attractive to the nursery industry, like dwarf growth or improved bark. And while at first sight this may seem as an advantage for bonsai, there has often been a preference for the more durable and faster growing wild species. For this article on the suitablity of different azalea varieties, I will generally ignore the flowers. When it comes to azaleas and bonsai, the satsuki azalea is often seen as the ideal azalea variety group. However, bonsai can be created out of any type of evergreen azaleas. The most important reason that satsuki azaleas are preferred for bonsai is that in Japan, satsuki bonsai enthusiasts are often first and foremost satsuki enthusiasts. A second reason is that with the dominance of satsuki and the importance of exhibitions, most other type of varieties bloom earlier. So in terms of logistics, it would be a challenge to show an azalea that is not a satsuki at a flower exhebition. Additionally, the rules of the competition may not allow varieties that are not recognized. That said, there are many satsuki that have genetics from other cultivar groups, like kurume and Belgian Indica azaleas.

The satsuki varieties do have some inherent advantages when it comes to bonsai. Some satsuki have small leaves and shorter internode growth. Furthermore, satsuki generally respond better to pruning than many other azalea varieties, producing more buds. Satsuki generally are more bushy and have slower growth, which can be advantages for bonsai. However, it is not actually true that satsuki azaleas were deliberately bred for their ability to grow trunks, though there are some varieties that are noted to have better characteristiscs for developing tapered trunks. Since it takes many decades to develop a massive trunk, varieties are adopted and becaome popular irregardless of their suitability for bulking up trunks. However, at some point in the future it may be considered that indeed a subset of satsuki were bred to be superior for this style of bonsai. It is very rare to find an evergreen azalea this a true species rather than a cultivated varieety, even in a botanical garden. So for bonsai, one would generally prefer satsuki azalea cultivars that are most suitable for bonsai. In this article I list the most famous ones.

Azaleas are a popular bonsai species and the satsuki cultivars are by far the most common azalea varieties used for bonsai. This article gives an overview of some of the most common satsuki varieties and explains their advantages and popularity. The most popular variety by far is ‘Osakazuki’¹. This is a pink flowering version of Rhododendron indicum and there is no indication it is a hybrid with genetics from a different species. Most landscape satsuki in Japan are ‘Osakazuki’ This variety shows the typical narrow leaf of R. indicum as well as the compact bushy growth habit. Because it is a durable tough variety, it is the ideal variety for satsuki bonsai that are on display outside of the flowering season. Since it is such an old variety that was mass-planted all over Japan, there are many old specimen of ‘Osakazuki’.

Some believe there are different versions of ‘Osakazuki’ that can be told apart and that 'Osakazuki number 2' is a form with superior foliage. It may also be that think pink mutation of Rhododendron indicum has been collected many times from the wild population, and that there are many distinct 'Osakazuki' that are too similar to tell apart. And because ‘Osakazuki’ is said to be at least 300 years old, it may also be that there are different strains of ‘Osakazuki’ that can all trace back to the same original plant, but different clonal lines have slightly diverged over time. ‘Osakazuki’ has produced several sports with a different growth habit. The most famous sport if ‘Chinzan’, which has smaller leaves than the original.

At every satsuki bonsai exhibition you will always find at least a few 'Yata no Kagami' and 'Kinsai' are the second most common varieties for bonsai. The former in many respect is similar to ‘Osakazuki’, however the flowers are larger and or a more salmon orangy-red. Additionally, 'Yata no Kagami' produces pale coloured sports, ranging from paler spots or egg-shaped patterns in the center of each petal, to almost entirely pale flowers, sometimes only the tips maintaining the original reddish colour. 'Kinsai' is a quite different and distinct variety, having some of the most narrow leaves of all satsuki. It is praised for it's growth rate and ability to trunk up during field growing. But what makes 'Kinsai' stand out the most are it's tassled flowers. These flowers with narrow strips of red petal, give the plant an unusual and supernatural look.

The first Japanese book on satsuki dates back to 1670, but the Japanese have very likely started growing satsuki many centuries before that. For a long time, satsuki were grown as potted plants for their flowers. The type of flowers that were popular must have changed throughout the times, and this is not well-documented. But at the start of the 20th century, satsuki with very large flowers were all the rage. At the same time, bonsai techniques for growing pines and maples were becoming more advanced, in part through the introduction of metal wire. An important change in how satsuki were cultivated ooccured when a farmer discovered that the vulcanic pumice found in the Kanuma region made an excellent substrate for growing satsuki. Having been a waste product and a nuisiance to rice farmers before that, Mr. Shinzo Akimoto of Angyo popularized it's use for satsuki cultivation.² This also changed the geographical shift of satsuki nurseries towards the Kanuma city in the Utsunomiya region, about 200 km north of Toyko. With the kanuma substrate, horticulture practices improved and the skills of growing satsuki with large trunks were obtained. This allowed for azaleas as bonsai of superior quality. And it caused a shift towards satsuki varieties with smaller flowers.

One such variety was found in the middle of the 19th century, at Shoyo En garden at Rinno-ji temple near the city of Nikko. This variety was later named ‘Kozan’. Because Kobori Enshū was one of the garden designers of Shoyo En, and considering that Kobori Enshū used satsuki from the Kyoto region for some of his other gardens, it is possible that ‘Kozan’ originally came from Kyoto, and was known there under another name. More likely, ‘Kozan’ is a chance seedling that occured in Shoyo En, and it's parents came from Kyoto.³ Whatever its origins, once discovered ‘Kozan’ became a popular variety widely cultivated. And since it has small flower and leaves and grows relatively slowly, ‘Kozan’ became the key variety for this new trend of satsuki bonsai. Besides the small flowers, ‘Kozan’ also has the ability to form massive trunks. So by the 1920's, ‘Kozan’ was widely cultivated.

As Japan recovered from the second world war and both bonsai and satsuki experienced a huge boom, those with foresight that had planted ‘Kozan’ for field growing, now had massive satsuki trunks to train into bonsai. Because ‘Kozan’ was so popular and widely grown, it also produecd many sports. ‘Kozan’ itself is a simple very pale link flower. The most common sport of ‘Kozan’ is ‘Nikko’, which sports darker shades of pink alongside the original pale shade. ‘Nyohozan’ is a version of ‘Kozan’ with a strong blotch that gives a flower with a stronger contrast. Because of all these excellent traits, ‘Kozan’ is the satsuki variety most associated with bonsai. Additionally, it has been used in extensive cross-breedings, producing many new varieties. Most new satsuki varieties can trade their lineage back to ‘Kozan’ at several different spots in their family tree. This makes ‘Kozan’ the shogun of satsuki bonsai.

One of the more recent sports from the ‘Kozan’-group is ‘Hi-no-Maru’. This variety has a unique flower pattern with a central red round spot on a white background. This produces the same effect as the Japanese national flag, and thus was given the same name; 'ball of the sun' and has naturally become quite popular. As a sport, ‘Hi-no-Maru’ shares most of the plant habit and traits with ‘Kozan’.

Considering that ‘Osakazuki’ and ‘Kozan’ and it's sports are the most popular varieties for bonsai, it only makes sense to try to combine these traits in a new azalea. ‘Korin’ is therefore the product of crossbreeding ‘Kozan’ with ‘Osakazuki’, leading to a variety that gained a lot of popularity itself. Additonally, ‘Korin’ has also produced sports and have been extensively used as a parent in additional breeding. For a lot of breeding work, ‘Korin’ has cross-bred with a satsuki with impressive flowers, with ‘Korin’ using acting as a source for desirable plant habit. ‘Korin’ has the rapid growth and narrow leaves similar to ‘Kinsai’, and combines the flower colour of ‘Osakazuki’ with the more symmetrical flower of ‘Kozan’. If today, one was to decide to field grow satsuki trunks for several decades, completely focussing on bonsai for out-of-flower exhibitions, ‘Korin’ would probably be the ideal variety for such a project.

‘Osakazuki’, ‘Kozan’ and ‘Korin’, and their sports, are the best satsuki for bonsai.