The Q&A Archives: Bleeding Heart & Black Walnut

Question: I inherited many bleeding hearts when I bought this house a few years ago. They do not blossom. I suspect the reason is that the black walnut tree in my yard is now huge (& beautiful)& that its canopy is over the bleeding heart plants. Could the toxin in the soil be the cause of their not blossoming?

Answer: Black walnut (Juglans nigra) has a reputation for being allelopathic--that is, for inhibiting the growth of other plants. Small amounts of a substance called juglone are released by the tree roots, but a far greater amount of this growth-inhibiting chemical is found under the canopy of the tree.

Bleeding heart is sensitive to juglone. Some plants that are tolerant include: arborvitae, cedar, catalpa, clematis, daphne, elm, euonymous, forsythia, hawthorn, hemlock, sycamore, astilbe, begonia, bellflower, orange hawkweed, hosta, pansy, phlox, marigold, primrose, snowdrop, sweet woodruff, trillium and zinnia. Since your walnut tree is there to stay, try to plant one of the less-susceptible plants in the vicinity of the trees roots or canopy.

And, if you relocate your bleeding hearts to another shady area, they'll probably perk right up!

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