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Tuesday - September 27, 2011

From: Rockville, MD
Region: Mid-Atlantic
Topic: Invasive Plants, Propagation, Seeds and Seeding, Trees
Title: Eliminating black locust volunteers in Rockville MD
Answered by: Barbara Medford

QUESTION:

I am a landscape designer whose client has a very large, mature black locust in her front yard. Not surprisingly, she also has multitudes of black locust volunteers popping up all over her yard. The large tree will stay, but how can we safely remove the volunteers and discourage any more of them from coming up? For what it's worth, the tree is native to our area. Thanks for your help!

ANSWER:

From our webpage (which see) on Robinia pseudoacacia (Black locust):

"Because this species is well-adapted to establishment in very poor soil, it has been widely used for land reclamation projects. The eagerness of Robinia pseudoacacia to establish just about anywhere has a dark side; Black locust is often considered an invasive species and a garden thug because it spreads very rapidly by root sprouts and by the copious seeds it produces."

This tree is a member of the Fabaceae, or pea, family with the characteristic long seed pods. The sprouts seen are probably a combination of seedlings and root sprouts. You are correct, it is native to Maryland, as well as the other 48 states and large portions of Canada, as seen in this USDA Plant Profile map on the locations of the plant. Another excerpt from our webpage:

"Its wood, renowned for its toughness, belies its habit of shedding branches in high winds. Finally, its thorns are vicious to anyone attempting to work in or around the tree. This species and its various cultivars and hybrids should be rejected for most landscape uses because of the trees many bad habits."

Your client probably inherited the tree from a previous owner, or it was accidentally planted by birds or other animals, so we won't lecture too much on investigating any plant for its nativity or invasiveness before planting. Our first suggestion, which may not be too practical, is to get the tree out of there, make sure all the leaves and seedpods are raked up and removed from the property, and the roots ground out.

As for preventing further sprouts, here's the plan: Patience and Persistence.

Step 1. Careful policing of the area around the tree and immediate removal of the seed pods comes first.

Step 2. Clipping the root sprouts as far down in the soil as possible.

Step 3. Repeat Steps 1 and 2.

Herbicides, as we are sure you know, are going to be ineffective on root sprouts; the sprouts themselves may brown, but the roots from which they spring are unaffected because they are sheltered by the earth. Sprays would easily float on the wind, killing things you did not intend to die, contaminating the soil and doing virtually nothing to the offending tree.

We have been inundated, during the terrible drought in Texas, with questions about live oak sprouts. This is not quite the same thing because live oaks are excellent landscape and shade trees, and widely cultivated in Central Texas. However, they seem to be much worse in setting root sprouts this year because of the stresses the weather has put on the trees. The sprouts coming out of the roots (and those roots go waaay out, beyond the dripline of the tree) constitute mini branches with leaves on them. This is the tree's survival plan, providing itself with more leaves to produce nutrition for the tree. That's the reason we recommend stump grinding when an invasive tree has been removed, because as long as those roots are in the ground and can put up sprouts, that tree is still alive, not what you had in mind.

One last plug-Mr. Smarty Plants says the best way to control invasive plants is to never plant them, and investigate any tree thoroughly before planting.

Pictures of thorns on locusts

 

From the Image Gallery


Black locust
Robinia pseudoacacia

Black locust
Robinia pseudoacacia

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