Sunday, April 25, 2010

Eucommia - Hardy Rubber Treee

Eucommia ulmoides

A distant relative of the Elms; the Hardy Rubber Tree is a native of China where it is now extinct in the wild. However it makes an excellent vigorous, decorative, shade tree and has been planted in not only China but also in Europe and North America however nowhere abundant. It is a relic tree that was once widely distributed in Europe and North America during ancient times. Some such fossils date back to 35 million years ago.
It grows very fast to 60 feet or more and under ideal conditions has been known to reach up to 100 x 80 feet with a trunk diameter of 3.5 feet with a dome shaped spreading canopy. Some records include: fastest growth rate - 6 feet and 0.5 inch diameter;
5 years - 12 feet with 3 inch diameter; 15 years - 33 + feet; longest lived - unknown but definately well over 100 years. Some large trees are known to grow in:
Cincinnati, Ohio - 56 x 72 x 3.5 feet; Westtown School in Westtown, PA - 50 x 60 x 3 feet
The leathery foliage appears early in the spring and is oval, taper pointed, very glossy dark green above, light green beneath. The toothed leaves have prominent deeply impressed, lateral veining and droop. They reach up to 9.5 x 4 inches in size and turn golden yellow in fall.
When the leaf is torn, thin strands of rubber often join the 2 halves.
The male and female flowers appear on separate plants in early spring, are very small, without petals and appear on old shoots.
The fruits are winged, green keys up to 2 inches long in clusters with each key containing one seed.
The bark is gray-brown and deeply fissured.
This is the only tree originating in temperate regions of the world that produces rubber ( the others all native of the tropics ) though the latex is in quantities too small for this tree to be used as a commercial crop.
Eucommia ulmoides is the one and only plant in the Eucommiaceae family and genus.
Hardy zones 4 to 8, it does suffer from occasional winter damage and remains stunted in the Ottawa Valley of Canada. Prefers full sun and moist, fertile, light, well drained soil. Easy to grow it is very drought tolerant as well as tolerant of heat, clay, urban conditions and alkaline soil. It is not tolerant of waterlogged soils and flooding. An excellent shade tree with a dense canopy and strong branches that are storm resistant; it is resistant to disease making it reliably long lived. I highly recommend the Hardy Rubber Tree as a landscape tree for much of the eastern U.S. and southern Ontario, Canada and it is excellent for street plantings and parking lots. It is unfortunate that most landscapers only know 10 kinds of trees with this not being one of them.

* photo taken on April 18 2010 @ U.S. National Arboretum, DC

* photos taken on May 16 2010 @ Cylburn Arboretum, Baltimore, MD

* photo taken on 4th of July @ U.S. National Arboretum, D.C.

* photos taken on August 4 2010 @ Birnam Arboretum, Stratford, Ontario

* photos taken on Aug 25 2011 @ Scott Arboretum, Swarthmore College, PA


  1. Those leaves are beauties -- I'd love to know more about the tree. :)

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  3. Here is all my research on this tree. As for the mature size; I think they can exceed 3.5 feet in trunk diameter however there really are none over 100 years in North America and the only ones left in China are in cultivation. No available on longeavity however just like other relic trees such as the Ginkgo and Dawn Redwood this tree seems to be ignored by pests and disease. I'll place my bets that the Hardy Rubber Tree can survive for hundreds of years. The climate of much of China mimics that of eastern North America with cold winters and hot humid summers. Hardiness has not been fully tested however is certainly at least -22 F ( -30 C ).
    Most certainly an excellent tree for replacing borer killed Ash in Ontario and the U.S. Midwest.