The walnut could very well cause problems but you shouldn't have much to worry about with the hickories. They DO produce juglone as well, but in concentrations far lower than that of the walnut and are generally not considered much of an issue in this regard.

A great many plants are resistant to juglone, including most perennials. It is easier to list those that are intolerant :-) Do a Google search under juglone resistant plants and see what appeals.

One of the other factors involved in underplanting these trees has nothing to do with allelopathy and juglone intolerance. And that is the difficulty in getting plants to establish in the root zones of any large trees. The larger, more aggressive root system of the trees hog all available soil moisture and nutrients and smaller plants just cannot compete. And it's hard to dig through all those roots to prepare a proper planting hole! Start small and provide the necessary TLC in the form of additional watering and even fertilizing to help get the little guys properly established.

We don't have any hickory trees, but we do have several black walnuts on the land we live on, and have had good success with juglone tolerant perennials near them. I agree with gardengal48 that you may experience more of a challenge from the roots of the trees interfering with planting and moisture more than the juglone. Growing from seed may make the landscaping process easier, rather than trying to dig holes for larger nursery container plants.

Here are some links to some lists of juglone tolerant plants. Keep in mind though that sometimes various lists will contradict one another about what is juglone tolerant and what isn't:

http://ohioline.osu.edu/hyg-fact/1000/1148.html

http://wihort.uwex.edu/landscape/Juglone.htm#Trees&Shrubs:

http://www.wvu.edu/~Agexten/hortcult/fruits/blkwalnt.htm

http://pubs.ext.vt.edu/430/430-021/430-021.html

You may want to try to select perennials that also tolerate dry soil, depending on much the trees root systems are dominating the land you live on.

Sometimes I find it helpful to research the natural forest habitat of trees...what forest-expert types usually call the "forest alliance"...and then look for the plants that naturally grow underneath them what's known as the "understory" or "herb layer". These types of native plants will likely grow the easiest and require the least maintenance.

Not sure what kind of hickory trees you have, but if they're naturally growing in your yard, they would be one of the Caryas...possibly Carya ovata (Shagbark Hickory) or maybe Carya glabra (Pignut Hickory). Depends of course on what area of the country you're in.

Here's some info on forests with hickories in Maryland:

http://www.dnr.state.md.us/wildlife/Md_Veg_Com/10_.asp

Look for what's listed as growing in the "herbaceous layer", "herb layer" and "shrub layer" and you may get a better idea of what will naturally grow well beneath hickories.

Weave,

Native perennials will do best in such a place. Under my Hickorys are the short early and tall late Tradescantia subaspera and T. ohioensis, Claytonia virginica or Spring Beauty, Trillium cuneatum, Cimicifuga racemosa (has a new name but I forget it), Tiarella or Foamflowers, Heuchera americana, and Hymenocallis occidentalis/caroliniana or White Spider Lily. Orchids are no strangers to Hickorys but one must avoid salt and chemicals with them. Developing beneficial soil organisms will help any plant community.

These are things I have seen in clay soils and sandy loams.

Many kinds of non-native bulbs will colonize in lighter soils under these trees. Epimediums are first class and a gamble- there are so many kinds avalable these days. Some will grow in heavy clay and on limestone and can be extremely drought tolerant. Others need Azalea conditions.

Mike519

I have almost the same problem, only I have 1 hickory and about 15 black walnut trees. Penn State has a great publication titled "Landscaping and Gardening around Walnuts and other Juglone Producing Plants". You can find it at http://hortweb.cas.psu.edu.

My personal experience is that most shade loving plants with the exception of azalea do very well under the walnut trees.

Good luck. Carol

How long does the toxicity last? We removed a mature hickory in January 2020 and I want to plant milkweed under it this fall. Milkweed is not on the list of plants that can tolerate hickories.