Are peonies affected by black walnut trees?

Peonies and black walnuts are not a great combination. Like many other plants, peonies do not grow well near black walnuts because of a chemical called juglone.

Black walnut trees release juglone especially from their roots, buds and nut hulls, but the chemical is present in all parts of the tree. Juglone’s job is to prevent other plants from growing to reduce competition for the walnut tree.

That means, your peony planted near a black walnut will struggle.

Symptoms of Juglone on peonies and other plants include:

• Yellow or brown leaves

• Wilting leaves

• Twisting leaves

• Stunted growth

Eventually the plant will die over time.

Some varieties of peonies are more susceptible to juglone than others but I haven’t been able to find any reliable research or documentation on which varieties are more of less affected. The safe bet is to avoid black walnut around any of your peonies.

Older and larger black walnut trees produce more of the toxin than young trees. So sometimes peonies and other plants may appear to be doing fine but as the tree grows, the peonies will eventually suffer.

I recommend you make a choice of rather to remove your black walnut tree altogether or transplant your peonies to a new spot well away from the walnut.

After removal, juglone does break down in the soil rather quickly, within two months. But as roots decay they release more juglone into the soil so it can be several years before the effect is completely gone.

A large tree with an extensive root system will take longer to decay than a small, young tree.

If you choose to keep both growing together I recommend removing the leaves and nut hulls from under the tree as they fall in autumn.

Other trees in the same family of black walnuts like butternut, shagbark hickory and pecan also produce and release juglone, but in a lower concentration than black walnut.