Plant of the Week
Black Locust
Latin: Robinia pseudoacacia
Fayetteville is enjoying an annual rite of spring: the blooming of the
sweetly scented black locust. The pendant clusters of creamy white flowers of
these 60-foot tall trees are in great abundance this year, probably encouraged
by the dry weather we "enjoyed" last summer.
Every year when the black locust bloom, I am struck by the beauty of the tree
and the odd fact that it’s so seldom grown as an ornamental in its own native
range. This member of the legume family is native from Pennsylvania to Alabama
in the Appalachian chain and on the Ozark Plateau in our part of the world.
The black locust often grows in little groves. It produces root suckers.
Foresters consider it a medium-growing species. The trunk grows about a quarter
of an inch per year. The trunks is usually tall and straight with most of the
closely held limbs near the top of the tree.
The inch-long creamy white, pea-shaped flowers are borne in six-inch long
clusters and are highly fragrant. The plant produces pods similar to those found
on redbuds. The leaves are compound with 11 to 20 oval leaflets.
Pink-flowered and thornless forms are sold in drier parts of the western
United States where the tree is often used as a landscape plant. Several
selections with golden foliage such as ‘Aurea’ and ‘Frisia’ have been developed
and are common in gardens of the Pacific Northwest. These golden leaf forms may
not hold their yellow color all summer in our heat.
The black locust is the third most important hardwood timber species in the
world, behind only eucalyptus and hybrid poplar, but it’s seldom grown in the
United States because of a borer that infests trees grown for timber. In Europe
and Asia, thousands of acres of the trees are planted for both posts and lumber
purposes.
The story of the popularization of black locust in Europe is an interesting,
if somewhat bizarre, tale. The tree was first introduced into Europe in the
early 1600s, but it was not until the late 1700s that it began to be promoted as
a plantation tree, especially for use in ship building. The decay resistance of
black locust is legendary. It’s said to last 10 years longer than stone. In
reality, it’s estimated to last 500 years when exposed to wet conditions and
1,500 years when kept relatively dry.
The principle European apostle of the merits of black locust was William
Cobbett (1763-1835), a journalist with a knack for getting crosswise with
authority figures. He was forced to flee England and arrived in Philadelphia in
1792. There he became a vocal opponent of the democracy movement in the United
States.
He especially attacked Thomas Paine, the author of The Rights of Man
and The Age of Reason. But what eventually lead to his leaving the United
States was his public attack of Dr. Benjamin Rush for medical malpractice during
the good doctor’s treatment of the dying George Washington.
But his stay in America changed him. When he returned to England, he began to
rail against the Crown. This lead to his involvement with the British worker
movement, which again resulted in his expulsion back to America in 1816. On his
Long Island property, he started a tree farm and became convinced of the merits
of black locust.
After two years, things had cooled down and he decided to return to England,
but not alone. After undergoing a metamorphoses of belief, he now considered
Thomas Paine a hero, so he had his body dug up and took it back to England with
him with the intent of building a monument for the American author. Salt in the
wound of authority, so to speak.
To support his English farm, Cobbett began promoting and selling black locust
seeds and trees. His 1825 book, The Woodlands, was the real catalyst for
popularizing the tree throughout much of Europe. During the years that followed,
a black locust craze swept Europe, not unlike the emu farming craze of recent
years.
Oh, by the way, Thomas Paine never got his monument. On Cobbett’s death, the
coffin in which his remains were kept was sold to a London secondhand furniture
dealer and the bones were discarded so the coffin could be resold.
The black locust is one tough tree. It grows on almost any soil, making it a
popular choice for planting on mine-spoil sites. It’s been reported as growing
on soils with a pH as low as 2.5!
Because it fixes its own nitrogen by means of nodules on the roots, the black
locus fertilizes itself. It’s exceedingly drought tolerant and is a popular
street tree in the low rainfall areas of western states.
By: Gerald Klingaman, retired
Extension Horticulturist
- Ornamentals
Extension News -
May 4, 2001
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