Download Release Date - Elvehjem Neighborhood Association

Release Date:
August 1, 2002
Contact:
Mike Maddox, Dane County UWEX Horticulture Agent, 608-224-3715
PLANTING NEAR TREES
Madison - Have your previously successful garden plants wilted and died all of a sudden this year? This may
seem perplexing when the problem affects some, but not all types of vegetable and flower species
Do you have a black walnut or butternut tree in the area? If you do, the tree or trees may be causing the
problem.
Black walnut and butternut produce a toxic substance called juglone in their roots, leaves and fruit. The
juglone is toxic to many plant species. Your plants may have not died in previous years because the tree's
roots had not yet reached the plant roots in your garden. This year, the black walnut or butternut roots
reached the susceptible garden plants' roots and damage occurred.
The susceptible plant takes in the juglone toxin through its root system. This causes leaves to turn yellow,
wilt and then die. Black walnut and butternut tree roots can extend a considerable distance. They commonly
reach out beyond the tree's dripline.
What plants are susceptible to this type of injury? Although researchers don't know all the plants affected by
juglone, evidence shows that juglone most commonly poisons potatoes and tomatoes. Other susceptible
plants include some apple varieties, eggplant, pepper, beans, cucumber, rhododendron, white and red pine,
white birch, cinquefoil and cotoneaster.
Black raspberry plants thrive around black walnuts and butternuts while the closely related black berry
quickly dies.
Controlling the problem is not easy. Planting shallow rooted species like lettuce and spinach near walnut
trees reduces the problem somewhat. Cutting down the nut trees will eventually solve the problem once all
the roots disintegrate completely. This may take 1-5 years depending on the size and amount of walnut roots
in your garden.
A steel or concrete barrier placed into the ground between the tree and susceptible species can help if you do
this before the roots reach that point.
Because the juglone is present in all the tree parts, do not use the leaves, walnut husks or shells as mulch for
a flower or vegetable garden.
For help with all of your garden & landscaping questions, please contact the Dane County UW-Extension
office at (608) 224-3721 or e-mail [email protected].