Wal-not!
by Rommy Lopat

ARTICLE FIRST APPEARED: 1998 Summer

TWG Editor: My thanks to Doris Taylor of The Morton Arboetum [630) 719-2424] for sending this list of plants sensitive to Black Walnut toxicity. Sent just in time, Doris, for shortly thereafter a landscape designer asked me for this very thing!

While many plants grow well in proximity to Black Walnut [Juglans nigra], there are others whose growth is inhibited by a chemical [juglone] it produces. This process of poisoning other plants to favor its own growth is termed, "allelopathy". Juglone is produced by all parts of the tree, including decaying roots. Therefore, toxicity can be detected for several years even after a Black Walnut is removed.

Plants sensitive to Walnut show signs of wilting, yellow leaves, stunted or slow growth, and eventually death (sometimes swift, sometimes slow). There is no cure for this curse.

Plants Proven Sensitive to the Black Walnut

Annuals and Vegetables: asparagus, cabbage, petunia, potato, tomato;

Herbaceous Perennials: autumn crocus, baptisia, columbine, lilies (Asian hybrids), peony, rhubarb;

Shrubs: blueberry, red chokeberry, contoneaster, Amur honeysuckle, hydrangea, lilacs, privet, potentilla, rhododendron, some viburnum species, yew;

Trees: European alder, white birch, crabapple species, hackberry, larch, linden, saucer magnolia, mugo pine, Norway spruce, red pine, white pine, and silver maple.

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