Are you seeking plants that will grow under the Black Walnut trees on your property?
Black walnut trees can be a tricky plant for gardeners, as this species of plant produces a toxic substance called juglone via its root system. Other trees that emit this toxic substance include butternut and Persian walnut trees that are grafted with black walnut. (Notably, persian walnut seedlings that are grafted onto persian walnut rootstocks do not produce deadly toxins that kill other plants.)
The juglone leaches out into the surrounding soil and it can kill nearby plants within a period of just 30 to 60 days. Some of the most susceptible plants include: Tomato plants; Blackberry bushes; Azalea; Mountain laurel; Apple trees; Blueberry bushes; Potato plants; Rhododendron bushes.
The toxic zone can extend up to 80 feet from the trunk of a large mature black walnut tree, though the typical no-grow zone usually extends 50 to 60 feet. This tree's tendency to kill off nearby plants is enough to leave many gardeners scratching their heads, wondering "what can I plant that will grow under a black walnut tree?"
Not to fear! Not all plants are sensitive to the juglone that's produced by the black walnut tree. There are a number of trees, annuals, perennials, shrubs, vines and ground-cover plants that are resistant to juglone.
Some of the most popular plants that are often planted near a black walnut tree include:
Crested Wood Fern
It appears that the black walnut tree actually enhances and promotes growth in a limited number of plant species, especially grasses such as Kentucky bluegrass.
Despite the fact that the black walnut tree's toxins can kill many nearby plants, they are still favoured by many for their beautiful appearance and their ability to prevent soil erosion and offer shade, particularly on pastures. They are especially popular in pastures.
It's important to note, though, that juglone is present in the black walnut tree's wood, bark and leaves. The wood chips can cause problems in some animals, particularly horses.
Composting black walnut leaves will result in the degradation of the juglone toxin, which breaks down in 2 to 4 weeks when the leaves are composted alone, or up to 2 months if they're mixed with soil and other compost matter. So it's generally safe to use fully-composted leaves on juglone-sensitive plants.