Walnuts can be great shade trees. Unfortunately, there are many plants that cannot grow under or even near a black walnut. This is because walnuts emit ‘juglone’ -- a chemical that causes many plants to yellow, wilt and eventually die.
The juglone is in all parts of the walnut, from its buds to its roots. The soil receives contamination from above as leaves and nuts fall, and from below as walnut roots do their job of emitting the juglone. The area directly under the canopy is the most challenging for gardeners. Farther away from the tree, the concentration of juglone may be less.
I can almost hear you thinking: “We’ll just chop the darn thing down then!” Not so fast... the roots will continue to emit juglone for years as they decay. The solution is to learn to love the walnut, and experiment with what will grow under it.
You can find many lists of tolerant plant species on the web and in books. We’ve found that experience varies, so it’s best to start slow and try a plant out before creating a carpet of it under your tree. We’ve also noticed that you may be more successful starting with younger, smaller plants, rather than mature specimens, especially with shrubs and understory trees.
Here’s a list of ten plants that may do well for you under your walnut:
- Cinnamon fern
- White wood aster
- Jack in the pulpit
- Woodland phlox
- Witch hazel
- Arrow-wood viburnum
- Black haw viburnum
For a more complete list of native species that may tolerate juglone in your garden, see http://www.edgeofthewoodsnursery.com/wp-content/themes/atahualpa351/pdf/juglans_tolerant.pdf
To help these plants along, if you have the time, remove leaves and nuts from the planting area as they fall. If you’re a ‘lazy gardener’ like me, you’ll just figure out which plants can handle the full brunt of the walnut and go with them.
If you are a composter, avoid putting leaves or nuts from the walnut in your pile, as they may still release juglone even after a period of composting.
If you start to get discouraged, google ‘black walnut recipes’. Your mouth will water and you’ll have renewed enthusiasm for finding plants that will live harmoniously in your landscape.
If you’ve had particular success with any native species under your black walnut, please leave a comment below.