Gardening Under Walnut Trees in the Ozarks

Twenty-eight years ago, we bought a couple of wooded acres in southwest Missouri and built a home that is on a rocky bluff. The goal was to turn this property into terraced beds that attracted birds and beneficial insects. We did not want to have a lawn to mow. That was the idyllic dream, but it took a while for reality to sink in that as we aged, we would need to amend our original garden plans. My husband built the terraces in his spare time. It took many years to build and taking care of the beds was becoming a time-consuming monster that we have been trying to tame. I am a self-taught gardener and I have made many a plant choice mistake. What looks good in a friend’s garden or at a nursery can become the bane of my life (i.e., invasive).

The land was typical of the Ozarks; very rocky, little topsoil, and wild. We had a plethora of native trees, black oak, Osage-orange, shagbark hickory, black cherry, ash, persimmon, redbuds, cedar, sycamores, and walnut trees. Our first terraces were around many of these trees along with several walnut trees. It was dark, dry shade and the black walnut trees produce a chemical called juglone, which occurs naturally in all parts of the tree. This is leached into the soil with the highest concentration of juglone in the soil directly under the tree’s canopy. It was a gardener’s nightmare to find plants that could survive these conditions.

My husband and I dug up the limestone rocks with our pickaxes and my trusty Pickmatic. We amended the soil with fresh dirt, compost, and added wood mulch to keep the weeds down. It was my job to find the plants and shrubs that could survive these conditions. We spoke to nursery men and women selling their plants at the local farmers’ market, and I read article after article of the toxicity of walnut trees with some ideas of plants that might survive. We annually added wood mulch to the woodland beds to make them neater, suppress weeds, and retain moisture in the soil. This may be helping the perennials to survive year and year by suppressing the juglone that comes from the walnut trees.

It took a lot of experimentation and losing many plants, but I did discover plants that will survive each year. I came up with a list, albeit not an extremely long list, of perennials and annuals that will exist under walnut trees. I do need to confess that my original objective was to remove all of those walnut trees, and we did remove a few, but we share our property with a lot of wildlife, and the walnuts help some survive the winter even if those trees created a lot of extra garden work.

What survives? Hostas and ferns. The bigger the better to stand out in the shade. The hostas do look their best in late spring and early summer. The heat in July and August does cause some leaf burning for hostas on the perimeter of the terraces where the sunlight pierces through the canopy of leaves. Also, the trees are sucking the moisture out of the beds. I have carried many water cans of rainwater that we capture from our metal roof, however, sometimes we do succumb to using a sprinkler to keep our plants going until the late summer rains come. 

Mayapples are native to our property and do well. Boxwoods will survive, but the variegated boxwoods may only last a few years before they give up from either the toxins or possibly vying for the same rainwater that the larger tree roots greedily steal.

Brunnera thrives and actually multiplies. I prefer the variegated type since the leaves provide more visual interest than the plain Jane all green brunnera. However, the plain Jane brunnera as a backdrop makes the variegated ones standout.

Liriope, lamium, and wild ginger make great ground covers – they thrive and spread. The deer trim back the liriope every winter (they ignore the liriope during most of the year but do become four-legged weed whackers to get rid of the old foliage and allow new to come up in the spring).

Celandine poppies provide bright yellow flowers that are welcomed to give “light” in what can be a dark garden. They will multiply once established and then become invasive. I have become quite a mercenary with a spade as my weapon to thin them out.

Jacob’s ladder, Virginia bluebells, perennial geraniums (cranesbill), and heuchera come back without fail every spring, but I find that they are not as reproductive as celandine poppies, brunnera, and wild ginger. The lamium was probably a mistake to plant; it has thrived too well and suckers under the soil, so it is super difficult to dig it all out. But I just love the snapdragon type flower that it produces. I guess that is why I have not gone after it with the same perseverance as I have with the celandine poppies. Tall phlox and dwarf Oriental lilies come back each year (they are on the periphery of my woodland beds and get a little sun).

I am surprised that about a dozen or so Darwin hybrid tulips come up every year. We all know they are to be treated as annuals, but I must have gotten lucky with these tulips. The grape hyacinth may have had a better presence in this bed, but the deer seem to keep them in check before I can spray everything with a deer repellant. 

I have a clump of spiderwort that gets bigger with each year; another invasive plant but the juglone must keep it from going crazy. Caladiums, coleus, and impatiens are annuals that survive, plus they add much needed color to break up the many shades of green with the perennials.

Gardening is always a case of experimentation. Gardening under walnut trees is a work in progress and a learning experience. What I have learned is that if the plant does not survive or does not work, dig it up and find a new spot for it, give it away, or just compost it if it turns out to be too aggressive. Some plants may need to be shipped to the trash or burned to safely dispose of them. I hope you can benefit from my experiences with walnut trees; it is possible to grow annuals and perennials under these types of trees.

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