Juglone Explained: The Walnut Compound That Affects Plants and People

If you’ve ever noticed that tomatoes or roses die near a walnut tree, juglone is probably the culprit. It’s a chemical the tree releases to keep competition away. Think of it as nature’s own weed‑killer, but it can also cause skin irritation for us.

Where Juglone Comes From

Juglone (C₁₀H₆O₃) is found in all parts of black and English walnut trees – leaves, roots, bark, and especially the husks that surround the nuts. When a leaf falls or a root spreads, the compound leaches into the soil and water around the tree. That’s why you often see a clear “dead zone” under mature walnuts.

How Juglone Affects You and Your Garden

For most garden plants, juglone is toxic. It disrupts cellular respiration, so seedlings wilt, leaves turn yellow, and growth stops. Sensitive crops include tomatoes, potatoes, peppers, and many ornamental flowers. If you’re planning a new bed, measure at least 30‑40 feet from the trunk before planting anything that’s known to be juglone‑sensitive.

People can react too. Direct contact with fresh walnut husks or sap may cause itching, redness, or a rash. The reaction isn’t usually severe, but it’s wise to wear gloves when handling husks or pruning trees. Wash hands thoroughly after any contact.

If you want to use juglone deliberately, it works well as a natural herbicide. Sprinkle crushed walnut shells around unwanted weeds and water them in; the juglone will suppress growth without synthetic chemicals. Just remember that this method also harms any nearby garden plants, so apply it selectively.

Removing juglone from soil is tricky because the compound sticks around for months to years. Adding plenty of organic matter—compost or well‑decomposed leaf litter—helps microbes break it down faster. Aerating the soil and planting juglone‑tolerant species like corn, wheat, or certain grasses can also reduce its concentration over time.

When buying walnut products, such as natural dyes or extracts, check if they’re labeled “juglone‑free” if you have sensitive skin. Most commercial preparations remove the toxin during processing, but it’s good to confirm.

In short, juglone is a powerful ally for the walnut tree and a potential troublemaker for gardeners and skin‑sensitive folks. Knowing where it comes from, how it spreads, and which plants can survive its presence lets you keep your garden thriving while staying safe.