juglone - tolerant evergreens & neutralization

Asked January 1, 2020, 12:49 PM EST

Hello, After lots of experimentation and research, I’ve concluded my back row foundation bed plantings are dying due to juglone in the soil. We have a black walnut tree in the side yard, about 30’ feet from the NW foundation bed. I’ve given up, for now, on my ericaceous evergreens (rhododendron, pieris & mountain laurel). I’m wondering what evergreens I can replace them with that won’t grow too large for a foundation planting or can take heavy pruning.This is zone 5b and partly to mostly shade. Additionally, I’ve seen some articles discuss the role of pseudomonas and proline in metabolizing juglone, as well as the use of mulberry plantings around a black walnut tree as a means of neutralizing juglone beyond their root zone. Any insight on these approaches? I’d like to begin experimenting, as I don’t like the idea of cutting down the tree, but am also quite passionate about my ericaceous ornamentals. I’ve also considered buying large (24-36” W x12”D) plastic planting tubs, drilling holes for drainage, digging equal sized holes into the bed to set the tubs in, with a good few inches of gravel/pine bark & possibly some horticultural charcoal, and putting my juglone sensitive cultivars in these. I would appreciate any insight or ideas.

Ingham County Michigan

1 Response

Sorry to say that we have no magic information for dealing with juglone other than giving up on the juglone sensitive plants. What you are suggesting would be
highly labor intensive but might work for awhile, until roots punched through the containers. Containers would also restrict root growth which in turn could restrict plant growth. Best idea is if they aren't growing satisfactorily enough for you as is, get 'em out of there and put something in that will tolerate the juglone toxicity. Taking down an otherwise healthy black walnut seems nonsensical but also likely would not work as you wish, at least for a good while because the juglone would remain in the soil emanating from decaying roots for an unknown, possibly lengthy period of time.

While there may be ongoing research into neutralizing soil juglone, we have nothing to sink our teeth into to date and proceed as we have been. If you haven't read the Morton Arboretum writeup on black walnut, it is one of the more comprehensive reports complete with plant lists. Read more here:
https://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/plants-tolerant-black-walnut-toxicity

Good luck!