Black Walnut emits Juglone but there's still lots of stuff you CAN plant under there so don't be discouraged. Hostas do well and many other shade plants. Several of the links below will have a list of plants that are tolerant of juglone but you may want to experiment with other plants as well.

Here is a link that might be useful: google search

We have 58 acres of black walnut trees and I have yet to find anything at all that they discourage. Hostas, Heuchera, and daylilies are completely unaffected as are all the the other various perennials I grow. The full sun perennials are well away from the trees, but the shade and part-shade plants are shaded by these trees.

My advice is to just plant and see what happens. If you look at the list of things that supposedly don't grow under walnuts, you will miss having some really pretty plants!

Quite a number of plants also have a bit of toxicity to ward off plant competition (it's called allelopathy). Black walnut is the textbook/classic example, but also it has been noted to varying strengths in rice, sorghum, sweet sumac, quite a few aquatic/marsh plants and tree-of-heaven.

In black walnut, the concentration of the toxin is most pronouced at the dripline. As people have already mentioned, some plants have no problem with the walnut--but any plant in the Solanaceae family (Potato/tomato/eggplant family) will bite the dust.

I read you are suppose to plant 50 feet from a black walnut if the plant you are putting in can't take the black walnut. I know it is not good to put a garden in near a black walnut. I learned that the hard way before I found out black walnuts can be toxic to some plants. My dayliles love being planted at the base of one though.

Blackberries and Raspberries to well in the vicinity of Walnuts...just make sure the berries get lots of sun....

I'm surrounded by Black Walnut trees on my three acres. I've learned to live with them! Two shrubs that absolutely THRIVE on their own under Black Walnuts are wild black raspberries (not really great "shrubs", but the berries are delicious!) and spicebush (lindera benzoin), which is a beautiful shrub, and turns yellow in the fall.