Though they are beautiful natives, black locust trees may be pests

Backyard Q&A

In the Garden

October 19, 2003|By Dennis Bishop | Dennis Bishop,Special to the Sun

I was planning to plant some black locust seedlings on our property, but I now understand it has some problems. Do you recommend this tree?

I am very fond of the black locust tree (Robinia pseudoacacia), but I cannot recommend it for planting. It has a number of disease and insect problems, and has the rare distinction of being a native tree that is also considered an invasive species.

If you notice large stands of browning trees along the roadside in mid- to late-summer, they are probably colonies of black locust. The tree's most troubling pest, locust leaf miner, causes the brown appearance when it invades and destroys leaf tissues. Black locust is an aggressive tree that spreads quickly by seed and by underground roots. It can invade disturbed areas and prevents other native plants from growing. For this reason, some consider it an invasive plant.

Others have taken advantage of this aggressive quality by planting black locust on land reclamation projects, both here and in other countries. It will grow on very poor soil. Black locust produces attractive, fragrant white flowers on 4- to 8-inch long racemes in May or early June. As the trees mature, they develop a high leaf canopy, which produces a beautiful light dappled shade.

Dennis Bishop is an urban horticulture educator for the Baltimore office of the Maryland Cooperative Extension Services. If you have a gardening or pest problem, you can call the Home and Garden Information Center hot line (Monday through Friday, 8 a.m. to 1 p.m.) at 800-342-2507. You can also e-mail questions, order publications and diagnose plant problems by visiting the Web site www.hgic.


1. Did your bulbs arrive before you were ready to plant them? Be sure to store them in a cool, dry place. This will prevent disease and keep them dormant.

2. Early fall leaves can be mulched with a mulching mower and left to lie on the ground. They will break down and feed the lawn next year.

3. Bring in semi-hardy plants like patio hibiscus before the first hard freeze.

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