by Randy davis

Last month we delved into the world of Elms and found that there are many interesting aspects of that tree genus, including its obtuse history and entry into the art of Bonsai. This month, through requests I've received in response to last month's article, it might be of interest to discuss Ulmus parvifolia in a little more detail. Ulmus parvifolia, better known by its common name of "Chinese elm" or "Chinese evergreen elm", is the most commonly used elm for bonsai not only in the United States but in fact the world. Owing to its horticultural history being the most focused on species as a replacement tree that is resistant to Dutch elm disease, it has had many cultivars selected over the years and now numbers at least 50 or more.

Along with the species, 8 of the cultivars with "Seiju" and "Corticosa" being the most popular, are used as bonsai. All of the cultivars can be broadly categorized into two basic groups; the smooth bark group and the rough bark group. Within the groups, various forms exist including large growing, dwarf, contorted and weeping. As you can tell, it can get quite confusing to the uninitiated. So let's just dwell on the species and the 8 cultivars, which will give you a good idea of the rich diversity of this elm.

The Smooth Bark Group

This group has the largest number of cultivars for the species as a whole, of which 5 are used for bonsai. The smooth bark group is charac--terized by the bark being relatively smooth during the entire life of the tree. The bark is not completely smooth, but is rather and more correctly termed "Flaky", as it flakes off as the tree gains age and girth. This flaking of the trunks bark makes for a mottled effect of predominately Grey with Brownish-red splotches and is the common feature of the species and all of the cultivars in this group. Trunk girth of this group is rather slow to develop even when grown in the ground, but more markedly so when grown in a container. It is not uncommon for container-grown material to be pencil-sized for years in some of the cultivars such as Catlin and Frosty. For bonsai, it is recommended that this group be grown and developed in the ground for a number of years to develop reasonable trunk girth in advance of initial bonsai training.

Parvifolia (the species) - The species is by far the most used for bonsai and is seen in every bonsai nursery in the country. More often than not these trees are imported from both China and Korea and are trained in more of a "penjing" style rather than the traditional Japanese bonsai style.

Catlin - This cultivar is very similar to the species but is differentiated by its smaller and more diminutive leaves. The growth is slower than the species, and girth is very slow to develop. It is not found in the general nursery trade but can be found at the larger bonsai shows and should be used more often than it is.

Catlin Contorted - This is a very dwarf contorted form of Catlin and is very difficult to find in the trade. It is available through Evergreen Garden Works on the web, where they also have very good information on its culture. This is one of those dwarfs that is very slow-growing and often only develops a single root, which must be worked on carefully to develop a well structured root system.

Drake - I only mention this cultivar in that it was one of the very first cultivars in the United States to be used on a commercial scale in the nursery trade. It is very similar to the species in growth habit. It was developed and introduced by Monrovia Nursery located in Southern California in the 1950's. It is not often used anymore but examples of it surely exist in the Western part of the United States.

Frosty - One of the only variegated forms of this elm. The growth habit in the ground is a tall thinly clothed tree. The leaves are the feature of this tree, with the leaves sporting white teeth around the leaf which are very prominent in the spring and early summer and becoming less prominent as the summer progresses. This cultivar is very slow to develop trunk girth unless grown in the ground.

The Rough Bark Group

The rough bark group is the smaller group in this elm, but is widely grown and used as excellent bonsai material. The rough bark group is charac-terized by its thick corky bark which comes with age. The cultivar "Corticosa" (or Cork bark) is faster at developing the corky bark than the other cultivars and is particularly fast when it is grown in the ground. All of the other cultivars are slower to develop the corky bark and should be ground grown to hasten their development. Some have said that there are multiple forms of these slower developing cultivars, but in fact it is just the way they have been grown. Seiju, for example, when container grown will retain a smooth bark for years before it starts to develop the corky structure, which is why it should be grown in the ground for a number of years.

Corticosa - This is the "Cork bark" elm so often found in the bonsai community. It is said to be of an unknown North American origin and is not generally available in the nursery trade. It is an excellent bonsai subject and can be used for both small and large styles. The leaves are rather large when the roots have enough room but will reduce quite nicely when subjected to bonsai culture.

Hokkaido - This is a dwarf cultivar of unknown Japanese origin and has the smallest leaves of the cultivars. It is an excellent candidate for small bonsai and will develop that corky bark at a moderate rate even when container grown. This cultivar should be grown in strong sun and the soil should be kept moist. Over watering during the winter months can cause root rot and is more often than not the reason for its demise.

Seiju - Another dwarf cultivar of American origin in the late 1950's. This cultivar was found as a sport on Hokkaido by Carl Young of California and has been exclusively grown as cuttings. Of all the cultivars, this is probably the most prized one for the bonsai enthusiast. This is another small leaved cultivar.

Yatsubusa - This cultivar is another introduction by Carl Young. It has most of the same characteristics of Seiju but the leaf is somewhat elongated and is a little slower to develop the corky bark structure. Not generally available in the trade, but not impossible to find if you look for it.

While all of these cultivars used in bonsai are Ulmus parvifolia, they do have some cultural differences that need to be taken into account. In general they are all strong growers with the exception of the dwarfs like Catlin contorted and, in our area, should be grown in the ground to get the maximum girth on the trunks prior to starting their bonsai training. The roots systems are generally aggressive and can be worked on equally aggressively except for the dwarfs. The fast growing cultivars like Corticosa when grown in the ground will develop "structural" roots rather quickly. Some refer to these roots as "water roots" which is true as the Chinese elm is a water hog, and it's these roots that are the water highway for the tree when it is in the ground and growing fast. The structural root system is what holds the tree in place in the ground and thus gains girth and length rather quickly as it extends deeper into the ground. Root pruning of these structural roots every other year along with top pruning in alternating years will give way to a very fibrous feeder root system which is so desired in quality bonsai. Good strong structural surface roots giving way quickly to feeder roots is just what the doctor orders for us bonsai enthusiasts.

One of the common misconceptions for this tree is that it can be over wintered in the house. This is one of the myths more prevalent with bonsai people in the colder climates. Why this is, I don't know. It is true that Ulmus parvifolia has a very wide distribution in its native habitat from northern China and Korea to northern Vietnam. In the United States, it is common to see them in Southern California and Florida where they are what they call semi-evergreen in that they only have minimal (50%) leaf drop in the winter months and never go completely dormant. While they will grow in those environments, their life span is diminished because of it. It is far better to let this tree go completely dormant outside in our local environments but give the roots some protection from the extreme winter cold when grown in a container. Ulmus parvifolia is an excellent bonsai subject and will work for small diminutive bonsai as well as large bonsai and everything in between. More often than not they are used in the "informal upright" style, but will also perform well as "Broom", "Natural", "root over rock" and "forest" styles. From a cultural standpoint, one should watch for black spot in the early spring and summer months, particularly in areas of high humidity. Using a good dormant spraying program with horticultural oil and lime sulpher, in addition to spraying with a fungicide in the spring when the fungus appears, will go a long way to eliminating the problem.

Wiring is usually done in the late fall and removed when the buds begin to swell in the early spring. While wiring can be done at anytime of year it is wise to watch for branch girdling during the rapid growth periods of spring and early summer. Branch pruning for ramification development can and should be done often for the fast growing cultivars such as "Corticosa". Owing to its ease of culture and excellent response to pruning, this tree is a good candidate for not only the experienced bonsai enthusiast but particularly well suited for the beginner. For the beginner, it is an excellent training tree on all of those techniques that we must learn in bonsai to expand our knowledge on what works and doesn't work. Ulmus parvifolia will give almost immediate feedback to the enthusiast because it's fast to response in both root and branch work. It is no wonder that it is one of the most popular trees used for bonsai in the world. If you have one of these trees in your collection, I'm sure you enjoy working with it; and, if you don't, it is one that you should look to add to your collection for years of enjoyment and learning.