Many common garden plants cannot grow near walnut trees due to a toxic chemical called juglone in the soil. Tomatoes, peppers, potatoes, and eggplant from the nightshade group top the kill list. Azaleas, blueberries, and rhododendrons die fast near walnuts too. Your tree's roots push this poison out into the dirt in every direction.
I found out about juglone during my second year of gardening. I put twelve tomato starts in a bed about fifteen feet from a big black walnut tree in my yard. Every single plant wilted from the top down within three weeks. The leaves curled up and the stems went soft even though I kept watering on schedule. A neighbor saw my dead garden and told me about the juglone problem right away.
Juglone sensitive plants react to even tiny amounts of this toxin in the ground. Walnut roots, fallen leaves, and rotting hulls all release juglone into the dirt. Black walnuts produce the most. English walnuts, butternuts, and hickories make it in smaller doses. The toxin blocks oxygen use inside plant cells. That is why your tomatoes wilt and die so fast once their roots hit the poison.
The toxic zone around your tree goes further than you might guess. Juglone spreads from the trunk to the drip line and then 20 to 30 feet (6 to 9 meters) past that edge. Juglone levels peak in spring and fall when root growth speeds up the most. You can't see it in the dirt. But your plants will show you where the zone ends by wilting right at the line.
Nightshade Family
- Tomatoes: Wilt and die within 2 to 4 weeks of going into juglone soil near your walnut tree.
- Peppers and eggplant: Show the same rapid wilt as tomatoes and can't survive any juglone in the soil.
- Potatoes: Tubers fail to form and the tops turn yellow before the whole plant goes down flat.
Heath Family
- Blueberries: Leaves turn brown at the edges first, then the whole bush dies back in one season.
- Azaleas: Stop blooming and drop their leaves early as roots rot from juglone damage below the surface.
- Rhododendrons: Large bushes decline over one to two seasons with leaf wilt and branch dieback.
Other Sensitive Plants
- Asparagus: Crowns rot in juglone soil and new spears come up thin, weak, and off-color each spring.
- Peonies: Fail to bloom and fade over two to three years if you plant them inside the toxic zone.
- Lilacs: Young plants die fast. Older bushes show slow decline with fewer blooms each year.
You can still garden near your walnut if you try walnut tree companion planting with safe species. Beans, corn, squash, carrots, beets, and most grasses grow fine in juglone soil. Raised beds with 12 or more inches of clean imported soil also work great. Line the bottom with fabric to keep walnut roots from growing up into your new bed.
Test your soil before you plant anything new within 50 feet of a walnut tree. You can buy a juglone test kit online or send a sample to your extension office. If it comes back positive, stick to your safe plant list or build raised beds. I moved my tomato garden to raised beds on the far side of the house. I have not lost a single plant since that move, and my harvests have been better than ever.
Read the full article: Growing Walnuts: 7 Key Steps
