Ulmus Rubra

by Randy Davis

Botanical Name – Ulmus rubra

Common Name – Slippery or red Elm

Description

Native to – Eastern United States from Quebec to northern Florida and west to the Dakotas and Texas

Botanical Information – Tree to 60 feet with spreading branches forming a broad flat-topped head.  The leaves are oblong and very unequal at the base where the leaf connects to the petiole. Leaves are doubly serrate, of firm texture and very rough above and pubescent beneath 4-7” long.  Flowers are red, form dense clusters close to the branch and appear in early spring along with the ripening seed.  A reddish brown pubescence of the bud-scale is very conspicuous in the spring as the buds are unfolding from which it gets its common name of "Red Elm".

General – First described by the French horticulturist Andre Michaux in the latter half of the 18th century during a 10 year stay in North America. This tree has had many names and was formerly know as U. fulva, U. elliptica, u. Heyderi and U. sibirica.  Its bark has been used as a medicinal for gastric ulcers, colitis, digestive problems, sore throat, coughs and other ailments.  Due to its medicinal properties, it is restricted in some countries.  Ulmus rubra is found in many environments and always found as a precursor tree in damaged soils along with U. alata.  It favors bright sunny locations and is very tolerant of many soil types from moist clay soils to hard rocky limestone outcroppings.  The bark of the tree is very fissured and with age forms a distinct white cork which adds to its beauty.  Little used for bonsai this tree should be used far more than it is. In its native habitat it is easily collected in the early spring before bud break when large caliper trunks up to 5 inches may be taken.  Branches are easily ramified and will become very tight and slender the more you work them making for fine winter specimens.  Leaves will reduce without difficulty and back budding is excellent, so typical of the elm family.  If you plan on collecting trees from the wild, large caliper trunk trees should be done over a number of years so as to develop taper and encourage wound healing while the tree is still in the ground. As with most collected trees once they are out of the ground and in a container, wound healing slows down dramatically

Cultivars – None known

Sun

In bonsai culture, Ulmus rubra should be given strong full sun during the spring and early summer months to encourage tighter growth and smaller leaves.  During the hot months of summer some light afternoon shade would be appreciated to moderate the soil temperature of the roots.

Temperature

Ulmus rubra in its native habitat are capable of withstanding extreme cold temperatures to as low as -37 degrees F during the winter and as high as 110 F during the summer months provided sufficient water is supplied.   Only in the far northern regions is it necessary to provide winter shelter for the root system of container plants. Containers covered in a blanket of snow or pine needles to the base of the trunk, is more than adequate.  Protection of the root system from continual freezing and thawing is the most important element of winter protection

Watering

As with all elms, Ulmus rubra will appreciate a continually moist soil.  The frequency of watering will depend on your soil mix and sun exposure during the growing season. Under dry conditions, the leaves will roll upward and inward and is an indication of the need of water.  Under wet conditions, the leaves will become flaccid and weak and drop from the tree which is an indication of root damage and should be resolved immediately. Watering should be done in the morning when you can sprinkle the leaves of the tree and be assured that the leaves will be dry by nightfall.  Keeping the leaves of this tree dry at night will help eliminate the encouragement of blackspot and other molds during the humid springtime weather of the Eastern United States

Fertilizing

Any balanced general purpose fertilizer is more than adequate for Ulmus rubra.  Fertilizing should commence in the early spring and continue through mid fall.  Application of the fertilizer can be at full strength at the recommended interval or a highly diluted form applied at each watering.  Fertilizer burn is indicated by a browning of the leaf along the primary mid-rib of the leaf.

Pruning

Major pruning should be done in the late winter and early spring, prior to bud break.  Minor pruning and ramification can be done anytime during the growing season. To encourage good ramification, let a branch grow 5 internodes in length and then cut back to the first internode.  Continual pruning of this type will produce tight ramified growth.

Wiring

Ulmus rubra is a strong growing tree during the spring and early summer and, is when most of the branches put on their girth.  It is for this reason that wiring should be done in the late fall, as soon as the leaves drop, and then removed in the very early spring.  The absolute best time to wire is right after leaf drop and before the first killing frost, as it is during this period that the branches are firm but pliable and respond to wiring well.  Once the tree is exposed to one or two killing frosts, the branches will have hardened and care should be taken in wiring, as they will be more subject to breakage during the wiring process. Guy wiring may be done at anytime of the year but you should be watchful of girdling.

Repotting

A finished bonsai of Ulmus rubra will require repotting about every 2-3 years, with 3 years being the more common timeframe.  As with most trees with vigorous root systems, Ulmus rubra will develop a mat of roots at the bottom of the container and begin to lift out of the pot, which is the signal for repotting the following year.  You can remove 1/3-1/2 of the feeder roots and trim back to the larger structural roots in the repotting process without damaging the tree.   For newly collected trees from the wild, it is important to take a larger root ball to ensure that you get enough structural root mass. Over time, begin to cut the structural roots back to encourage feeder roots to develop to an appropriate size for the finished bonsai.  Soil composition for a newly collected tree should be on the light side with more humus, so a 40% structural material, 50% humus and 10% clay composition would be more than adequate.  For a finished  tree, reduce the humus and add more structural and clay components to the mix to about 50% structural, 25% humus and 25% clay.

Propagation

Propagation of Ulmus rubra is usually from seed collected in late spring and planted immediately.  Cuttings may also be taken in mid summer when the wood is “half hard”  in 100% perlite, using a mild rooting hormone.  It is important to make sure the leaves of the cuttings are dry by nightfall to eliminate premature leaf drop during the rooting process.

Pests and Diseases

Ulmus rubra is for the most part pest and disease free but may be subject to blackspot mold during the wet humid springtime weather in the Southeastern US.  Any good fungicide that will control blackspot will be more than adequate to reduce the infestation.  Your watering regimen will greatly influence the development of molds in your trees.  By watering early enough in the day to ensure the leaves are dry by nightfall will greatly reduce any problems that might occur.  A winter spraying with a dormant spray (horticultural oil and lime sulpher) will control most pests and molds.  1 tablespoon horticultural oil and 1 tablespoon lime sulpher to a gallon water as a spray should be applied after leaf drop when you’re putting the tree away for the winter, one spraying in mid winter and then the final and most important spraying at bud break in the early spring.  As a side note, Ulmus rubra is very resistant to Dutch elm disease.

Source: http://feeds.feedburner.com/~r/louisvillebonsai/~3/262300183/post.aspx