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Elms

by Lionel Theron

The family Ulmaceae consists of Celtis, Ulmus and Zelkova. As a very good article has been written by Gail Theron entitled: "Celtis as bonsai" details of this genus will not be repeated here.

Zelkovas are rare in this country, the only ones we have seen are Z. serrata (Japanese zelkova) and Z. carpinifolia (Caucasian zelkova) and as we have had very little experience with them I will, in this article concentrate on the elms.

VARIETIES

There are many different elms listed and, as they hybridize readily and as there are many selected horticultural variations available they will not all be described, suffice to say that there are probably several that still need to be tried for their suitability for bonsai purposes. Elms are indigenous to the Northern Hemisphere including America, Europe and Asia.

Ulmus procera:

This is the English elm, so common in the hedgerows in the U.K. and which suckers so readily that it is avoided in all but the largest of gardens. The tree has been highly successful in the U.S.A. and is seen all over Europe and America, often as a parkland tree. This tree has been successfully used for bonsai purposes. In nature it reaches heights of up to 30m and some well known examples are many centuries old. Trees that were planted in gardens in the fifteenth and sixteenth century are still growing well!

Ulmus parvifolia (Chinese elm):

This is the elm which has particularly been found to be eminently suitable as a bonsai subject and deserves even more attention than it is currently getting and is resistant to the wood rot fungus often called Dutch elm disease.

The following varieties are reasonably well known:

U. parvifolia Catlin (Catlin elm):

a more or less evergreen variety with small dark green leaves which is widely used as bonsai, especially in California.

U. parvifolia Hokeido (miniature elm):

this is a very small leafed variant which is becoming more commonly available and is one of the most beautiful of elms.

U. parvifolia ?? (Golden elm):

This tree has a golden edge to its leaves which it may lose if it gets too much sun, especially late in the season.

U. parvifolia ?? (Kamura elm):

has variegated leaves splashed with cream and a little pink. They are the last of the elms to come out of their winter dormancy.

U. parvifolia corticata (cork-bark elm):

this variety develops the most interesting ribbed trunk much like the cork-barked black pine or the corticata variety of the Ginkgo.

U. parvifolia ?? (Sei-ju elm):

This remarkable elm from the Seiju-en Bonsai Nursery of Carl and Shin Young has miniature leaves and a cork bark and in addition is a vigorous grower combining the best traits of all the Chinese elms.

CULTIVATION

1. Soil.

In a bonsai pot these trees require a rich soil with extra leaf mould but must drain well. In a large training container pure coarse compost may be used.

2. Feeding.

Fertilizing should be specifically carried out for what one is trying to achieve:

a. Spring:

2.3.4. Spring feeding is most important as the winter rains will have leached out most of the nutrients from the soil. Remember that it is preferable to give light doses more frequently rather than one heavy dose. Do not use high nitrogen feed at this time as excessively sappy growth is prone to fungus attack.

b. Summer:

Feeds which are "high nitrogen" may now be used to feed the leaves. Seagro, Nitrosol, LAN, chicken manure or blood meal are all suitable.

c. Autumn:

Feeding in fall is very important to enable the tree to build up a good store of carbohydrates enabling it to grow strongly next spring and also to prevent small branches from dying back during the winter rest period. Feeding in fall also encourages the trunk to develop girth. Use Superphosphate and 2.3.4 plus Nitrosol.

d. Winter:

As deciduous trees do not take up nutrients when they are dormant, we do not feed in winter at all. In addition to the above program, one can also use micro-elements and growth hormones for specific problems or to assist in attaining special results but here it is best to consult further information on specialized feeding.

3. Position.

These trees seem to do best where they receive a few hours of morning sun otherwise they seem to be very adaptable.

4. Water.

Elms prefer a fairly moist environment and usually daily watering is sufficient. They should not be allowed to dry out totally.

5. Propagation.

a. Branch cuttings:

Both softwood and hardwood cuttings produce moderate success and are rooted in clean, coarse river sand, the cuttings having been dipped in rooting hormone.

b. Root cuttings:

An excellent success rate is obtained in this manner.

c. Air layering:

The method used, is ring barking, surrounding with compost and covering with dark plastic foil. This method is very successful.

d. Seed:

Seed produces excellent results but some either do not set fertile seeds or do not produce progeny true to type.

6. Development.

Some of the genetic variations are rather slow to develop whilst in the true species development is remarkably fast especially if they are developed to an advanced stage in a large container. Their growth is both apically and terminally dominant and consequently it is necessary to be on the watch lest heavy branches develop at the top of the tree or at the ends of branches whilst the the lower branches should preferably be thicker and also the tertiary branches should be thicker nearer the trunk with the thinner branches at the ends of the branch structure.

7. Defoliation.

It is unnecessary to defoliate most elms as their leaves are very small. If they should defoliate by themselves it is due to stress such as lack of moisture or using an unsuitable pesticide. The new foliage comes out strongly and this seems to have no major ill effects. The leaves of elms miniaturize considerably when the tree is grown in a bonsai container.

8. Pruning.

a. Summer:

It is necessary to nip frequently as otherwise one is liable to achieve undesirably long straight branchlets, a guide would be to prune back to one or two leaves after each spurt of growth.

b. Winter:

Whilst the tree is bare it is a good time to sort out branchlets and to trim each little branchlet to one or two eyes.

9. Wiring.

Directional pruning, anchoring and tying down methods may all be used but elms often require a considerable amount of training by wiring as many are prone to produce herring-bone patterns of branches which have to be sorted out to achieve a pleasing tree. Watch wires carefully as the branches and trunk can swell considerably in a very short space of time. Usually, unless the part being wired is very old, the new position is set quickly. When wiring thin branchlets great care must be taken or they may die back.

10. Potting.

Elms are one of the first trees to sprout in spring and we do our potting in late winter namely July through August. They are very tolerant of heavy root pruning. Frequent re-potting is recommended if the trees are to remain vigorous and healthy.

11. Pests and diseases.

Fortunately Chinese elms are resistant to the woodrot fungus known as Dutch elm disease and which attacks the new ring of wood just inside the bark on which the tree relies almost totally for its flow of sap and the tree loses branches or eventually the whole tree may die. This disease is difficult to treat and has seemingly made an appearance locally. Ulmus procera and other trees are prone to this dreaded disease. Chinese elms sometimes are attacked by grey scale and snout beetles and we have found a broad spectrum insecticide called Folithion is suitable and does not cause defoliation. The only other problem we have encountered is black spot and the fungicide Benlate controls this, again without the defoliation effect which some pesticides have on elms.

12. Styles:

Chinese elms lend themselves to be grown in any style and an open mind will enable you to try new methods and styles, some of them  will surely prove to be a contribution to the art of bonsai. These trees are ideal candidates for shohin and as they row to 15m lend themselves well to be grown as BIG bonsai.

In conclusion, the Chinese elms must surely be one of the best bonsai subjects - they invariably put out growth exactly where it is needed, they have wonderful small foliage of the most refreshing gree, are relatively disease free ad have all the attributes to make them close to perfect. It is probably fairly obvious that they are much loved in gardens and as bonsai.

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