Juglone is a substance in black walnut trees that can inhibit the growth of nearby plants. In a natural deciduous woodland setting, black walnut trees are surrounded by such common deciduous trees as eastern redbud, flowering dogwood, sugar maple and wild cherry. Wildflowers also grow near black walnut trees, unaffected by juglone. Select compatible flowering plants suited to your locale, and create a colorful shade garden under a black walnut tree.
Bleeding Heart (Dicentra spectabilis) is an herbaceous perennial that is native to Siberia, Japan, Korea and northern China. Bleeding heart is a low-maintenance plant that prefers part or full shade, making it ideal for planting under a black walnut tree. Bleeding heart plants are 24 to 30 inches tall. In April or May, the flower bears racemes, or long stems, droop gracefully with either white or pink heart-shaped flower clusters. The foliage fades after the plant blooms, and by mid-summer the plant is dormant.
Astilbe (Astilbe chinensis) is also known as false spirea. It is an herbaceous perennial native to Asia and North America. Astilbes need protection from the sun, growing best in partial shade to full shade. They are tolerant to juglone, and can be successfully grown under black walnut trees. Because trees pull a great deal of water and nutrients from the soil, astilbes benefit from supplemental fertilization. Provide plenty of water, and feed astilbes once in the spring and once in the summer using a 5-10-5 ratio fertilizer.
Tuberous begonias, especially the nonstop hybrids, provide a dazzling display of bright color all summer long. The flowers may be red, yellow, orange, salmon, pink, white or have a combination of color. Tuberous begonias are excellent flowers to plant in the shade of a black walnut tree. They are ideal for beds or borders or in containers or hanging baskets. Consistent watering will keep begonias looking their best. The soil should not be soggy, but it should never be allowed to completely dry out. Fertilize begonias regularly throughout the summer.