I want to plant a quick fire tree in my front yard in full sun. My neighbour has a black walnut tree ,about 60 feet away, that I just learned emits juglone which may kill my plant. Would planting the tree in a classic plastic tote 20 inches long x 14 wide x 16 deep
And submerging the tote in the ground solve the problem? Is the tote big enough for the roots? Would adding “premium mycorrhizal inoculant help? Any other suggestions?
Thank you!
Thank you for contacting Toronto Master Gardeners with your question.
While hydrangeas such as your Hydrangea paniculata ‘Quick Fire’ are not amongst the most juglone-sensitive plants, they can suffer if planted within 60 feet of a Black walnut (Juglans nigra). As you note, many plants are affected by the chemical juglone, which Black walnuts emit.
The Morton Arboretum, located in Chicago, posts a good summary of current research on the allelopathic properties of juglone, Black Walnut Toxicity :
“… while many plants can grow well in proximity to a black walnut, the growth of some plant species is thought to be inhibited by this tree. The term “allelopathy” refers to the relationship between plants in which one plant produces a substance that inhibits the growth of sensitive plants nearby. It should be noted that although it is ‘known’ as common knowledge in the gardening community, the allelopathic effect of black walnut has not been studied in depth. Much of what is known is based on one study done many decades ago. This means that any list regarding this topic is incomplete and some of the information may be anecdotal.”
The article goes on to say:
“Black walnuts produce a chemical called juglone, which occurs naturally in all parts of the tree, especially in the buds, nut hulls and roots. The leaves and stems contain smaller quantities of juglone, which is leached into the soil after they fall. The highest concentration of juglone occurs in the soil directly under the tree’s canopy, but highly sensitive plants may exhibit toxicity symptoms beyond the canopy drip line. Because decaying roots can release juglone, toxicity may occur for several years after a tree has been removed”
A response to a question similar to yours, addressed to the Master Gardener extension of the U.S. Department of Agriculture, Saving hydrangeas from juglone poison, gives the following advice:
“Typically, juglone-sensitive landscape plants should be located at least 60 feet from black walnut trees to avoid damage. Raised beds near trees will help minimize toxicity, but care should be taken to keep leaves, twigs, branches, and nuts out of the bed. Black walnut leaves, bark, and wood chips should not be used as landscape mulch or composted on garden plants. I’m a little surprised that 75 feet away from the walnut tree isn’t far enough, especially since hydrangeas are considered to be only moderately susceptible.
Juglone acts as a respiration inhibitor. Affected plants cannot exchange carbon dioxide and oxygen properly, which deprives them of needed energy for metabolic activity. The resulting wilting cannot be reversed.
Where walnuts crowd too close, build raised beds with root barriers in the bottom — concrete or rubber patio blocks are one option. Landscape fabric liner may not be sufficient. Hefty tubs are another option. You could raise those beds even higher: built at waist height, they could keep your back happy too–and would provide plenty of room for your hydrangea roots.”
It is interesting that one of the suggestions presented is to use a “hefty tub” to plant in. Your tote looks to be a good size and could work, but make sure that if you submerge it into the garden, you protect the tub from any walnut debris, that it has drainage holes in the bottom and locate it as far away from the neighbouring Black Walnut tree as possible.
If you are planting in a container, there may be a benefit to applying a mycorrhizae inoculation because the fungi normally present in soil may not be available in your container mix. In general however, the jury is out on the benefits of these inoculants. This response from the Toronto Master Gardeners gives some of the current thinking on this topic.
Good luck with your hydrangea.