A walnut tree in your yard might be killing your garden — here’s why

Walnut trees are prized for their majestic canopies, nutritious nuts, and ornamental beauty. But they also hide a darker side: they can quietly sabotage your vegetable patch or flower beds through a process called allelopathy — the chemical suppression of other plants.

According to international reports, the black walnut (Juglans nigra) and, to a lesser extent, English walnut (Juglans regia), release a substance known as juglone. This natural toxin can inhibit the growth of many nearby plants by altering the chemical composition of the soil.

Juglone is found in the roots, leaves, husks, and even the pollen of the walnut tree. When these materials decompose or interact with soil, juglone is released — making it difficult for some plants to germinate, grow, or thrive.

Crops especially sensitive to juglone include tomatoes, potatoes, eggplants, peppers, cabbages, beans, and many ornamentals like azaleas and rhododendrons. Symptoms can range from wilting and stunted growth to sudden plant death, often mistaken for disease or poor care.

What’s more, juglone can remain in the soil for months or even years after a walnut tree has been removed. This means simply cutting down the tree won’t immediately restore the soil’s balance.

To avoid problems, experts recommend:

• Keeping sensitive plants at least 15 meters (50 feet) away from walnut trees;
• Never composting walnut leaves or husks with garden waste;
• Planting tolerant species like corn, carrots, beets, onions, lilies, and ferns in walnut-adjacent areas.

Drainage also matters — juglone builds up more readily in compacted or poorly drained soils. Improving soil structure can help reduce its impact.

Interestingly, juglone is part of the walnut tree’s natural survival strategy. By suppressing competition, the tree ensures it has enough space, light, and nutrients. But in the context of a home garden, this self-defense becomes a silent disruptor.

Before planting — or preserving — a walnut tree in a productive area, consider its chemical influence. It may be more beautiful than beneficial when it comes to shared soil.