The poor black walnut, Juglans nigra, is often maligned. People seem to roll their eyes when they see they have on in their yard, or have to contend with one in their recent project. Some dislike it because it is the first to lose its leaves in fall a sure sign that winter is coming. Others know that it is challenging to grow much under these trees. We are here to tell you to take a deep breath and look to us, when it comes to plants that grow under Black Walnut trees – we have those!
Check out our plant search by characteristic and select ‘Juglans nigra‘ tolerance and see what pops up. It makes sense that many of our plants tolerate life under or around the stately black walnut. You see Black Walnut is part of our native plant community. They do not exist in colonies devoid of any other plants, they exist with others that have evolved to tolerate the naturally occurring toxins exuded by this plant forming a diverse plant community supporting a variety of animals. It is also important to note that Black Walnut, despite being infamous for its toxic presence, is not the only one that exhibits such characteristics, our friends the hickories, though to a lesser extent, also contain the chemical juglone. (So, too, do sycamore, red maples and the list goes on and on)
According to Plant Communities of New Jersey, hickories are found in early every plant community you can find in the state and Black Walnuts are found in quite a few as well. This means there is a great number of different plants that will thrive around them. Though it appears not much scientific research has been done on the survivability of various plants around walnuts and hickories, there are a lot of lists published and a lot of anecdotes regarding plant survivability. As we peruse these lists, something that becomes clear is that a lot of natives are tough plants and juglone may not phase them. We do caution that sensitivity varies even within a species, so it is best to test out a couple of plants before investing in an extensive planting under these trees.
Another factor affecting whether or not the plants suffer from the toxin is the drainage of the area. According to research by Rietveld, out of Wisconsin for the North Central Forest Experiment Station Forestry Sciences Laboratory, juglone is more available and present in poorly drained soils. According to the article juglone becomes less toxic as more organic matter encourages more microbes to break down the toxin before becoming available to surrounding plants. A soil that has a high moisture content creates an environment less favorable for those microbes and so the juglone builds up in the soil. This means that even the most tolerant of plants may have trouble in a poorly drained area around black walnuts and hickories. Also in this research, where native and non-native trees and shrubs were assessed for juglone sensitivity, the native plants (white oaks and tulip tree) faired much better than the non-native plants on average.
There are a number of trees and shrubs that are reported to grow fine under and around black walnut and hickories, you can find them listed in the resources we are referencing for the herbaceous list below.
Landscaping and Gardening Around Walnuts and Other Juglone Producing Plants (Penn State Extension)
Plants Tolerant of Black Walnut Toxicity (Morton Arboretum)
Black Walnut Toxicity (Purdue University)
The Walnut Tree – Allelopathic Effects and Plant Tolerance (Virginia Cooperative Extension)
If you are faced with planting under or around black walnuts or hickories, consider the following herbaceous plants:
Ferns – Ferns in general appear to be a safe bet when planting under Black Walnuts and Hickories. Ferns make nearly all of the lists of juglone tolerant plant species. In particular Christmas Ferns, Sensitive Ferns, Cinnamon Ferns and Wood Ferns are all mentioned in various publications.
Sedges – By now you know we have an ambition to become the source for any species of carex you are looking for and our own James Brown is looking to become the King of Carex, or is it the Prince Charming of Carex. Many species of native care will do just fine. Seersucker sedge, Bur Sedge and White-tinged Sedge are just a few to try.
Grasses – Nearly any of our native grasses are also a good bet.
Need a Vine? – Poison ivy is rumored to grow well among the Black Walnuts. We do not sell that, but we do have Virginia creeper which is equally tolerant of black walnuts.
How Far does the Juglone Go and How Long does it Last?
People always want to know how far the juglone goes and how long it hangs around in the soil after the trees are removed. As mentioned above, the amount of time it spends in the soil is directly related to the organic matter and drainage of the soil, the better the population of microbes to help break down the toxin, the shorter amount of time it remains in the soil. So if you are dealing with a plot that once contained black Walnuts or Hickories, you may want to consider aeration of the soil and soil amendment to increase organic matter. The toxin is found in the vegetative buds, nut hulls, roots, leaves and stems. Composting the leaves should break down the chemical. If you are nervous to try this, try composting walnut leaves separately and then plant some tomato, eggplant or pepper seedlings into the compost. These plants are extremely sensitive to the toxin, if the plants turn yellow and wilt, there is still juglone present in the compost and you may want to let it cure a bit longer.
Stay Calm and Keep Your Walnuts
In reality the most sensitive plants to juglone toxicity are the solanaceous vegetable plants like tomatoes, potatoes, eggplants and peppers. So change the location of the vegetable garden as far away from the Black Walnut as you can get and then plant lots of natives under and around these stately beauties and important trees for wildlife.
What is Your Experience?
What native plants have you noticed doing well or notice so well in the vicinity of a black walnut?