The Strong and Adaptable Black Locust

The black locust tree is prolific and unstoppable once established. You find these trees thriving after wildfires where nitrogen has been incinerated out of the soil.
By: Maureen Gilmer
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The black locust blooms resemble those of garden peas, indicating they share the same family. (SHNS photo by Maureen Gilmer / Do It Yourself)

If you were a tree, what kind would you be?

This often asked question by famed interviewer Barbara Walters has been put to world famous celebrities and politicians. If she asked me I'd be stymied by choosing one of my arboreal children over the others. But recently I've matured enough to admit a me-tree wouldn't be particularly beautiful, but it must be strong, tenacious as hell and all-American.

The Mo-tree is black locust, a native to the Appalachian Mountains southward to Georgia and west to Missouri and Oklahoma, and it's a member of the pea family. You can tell by the huge clusters of white pea shaped flowers in spring.

Like most other legumes, black locust doesn't depend on soil born nitrogen. It shares a unique ability to derive it from the atmosphere. You find these trees thriving after wildfires where nitrogen has been incinerated out of the soil. It is equally happy in sandy river beds with little fertility. It is a colonizer of disturbed ground.

The black locust is prolific and unstoppable once established. Its aggressive roots travel seeking water. In the wild, gophers and other burrowing rodents feed on them. This causes new sucker shoots to spring up wherever roots are damaged. This helps the tree spread more rapidly than by seedlings.

While this mechanism is very effective in the wild, it has not endeared the tree as an urban species. But such an easily propagated shade tree is desirable for rural homesites, frontier farms and ranches of the west. The tendency to sucker makes it a valuable erosion control plant for holding cut slopes and river banks.



The graceful compound leaves give locust foliage a beautiful texture. (SHNS photo by Maureen Gilmer / Do It Yourself)

The wood of black locust is exceptionally dense and resistant to decay. Settlers planted it for strong, long lasting fence post wood. Remember that before widespread logging of the California redwood forests this was an important foundation grade lumber. In the east the native trees had long been harvested for ship building as treenails or trunnels. These locust wood fasteners hold the exterior planking to the futtocks, the ship's internal ribs.

Fast growth made shade quickly in hot climates. The trees are so drought resistant they have naturalized in many parts of the arid Southwest. They tend to develop dense thickets useful to wildlife needing cover and nesting habitat. Some ecologists aren't happy about this eastern tree appearing in western wildlands.



Robinia pseudoacacia naturalized in the Sierra Nevada Mountains blooming in spring. (SHNS photo by Maureen Gilmer / do It Yourself)

In recent years black locust has become more civilized. Growers have crossed it with Robinia viscosa, another eastern U.S. native. The offspring are classified as Robinia ambigua hybrids which include really great cultivars with showier flowers. The most well known is 'Purple Robe,' a good suburban tree that blooms with wisteria-like deep pink to purple flowers.

It is large enough to create shade but it won't overwhelm a yard. Variety 'Idahoensis' is considered the best flowering and offers a more graceful habit. Its rich magenta to lavender pink blossoms are showy and more dense than the species. It will reach 35 feet tall and 20 feet wide at maturity.

Both 'Purple Robe' and 'Idahoensis' are widely available in the nursery trade from coast to coast. If plants are not in stock, the garden center will easily order it in the size you desire. Since this is a fast growing deciduous tree, it's not cost effective to plant them from stock any larger than fifteen gallon containers.

I wish I could mirror all the great qualities of the black locust. Sure, we're not the prettiest kids on the block, but we have staying power.

When things get hot, we don't get out of the kitchen. When the larder is bare we abide. When the hard winds blow, we stand strong. And though we might be unsuited to city life due to our tenacious and prolific nature, in the plains and the fields and the mountains we are country western stars.

Maureen Gilmer is a horticulturist and host of "Weekend Gardening" on DIY-Do It Yourself Network.

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