08/28/2026
Did you know I have my own test garden?
It's similar to what Mt. Cuba does, but a little different. Mt. Cuba tests garden worthy plants and pollinayor activity. I test tolerances. Here's one example... this is my juglone & road pollution (including road salt) test area. It's planted right up to the edge of the road which is a main, public road and snow route. You better believe that whenever there is snow in the forecast, or ice, this gets brined. Not only that, this is at the base of a mature black walnut, and right about now you start getting leaves and nuts dropping on the ground. The plants that go here need to be fairly tough. Most native plants will tolerate juglone just fine, because they co-evolved with them. Salt tolerance would be less, but brining is less heavy on salt than scattering rock salt. Road pollution doesn't really seem to be much of a factor that I've noticed. That being said, one family and one species did not make it. Any Ericaceae I've planted within the viscinity of the black walnut has died. I've tried Rhododendron, Leucothoe and Vaccinium. These grow just fine nearby, but outside of the drop zone of the black walnut. Underneath, they don't like it. The other species that did not survive here (though I have tons growing everywhere else) is redosier dogwood (Cornus sericea). I planted several, and it took a few years but eventually, all died. I believe the issue for those was the juglone, since they were far enough from the road to not get hit much with any brine or salt. I've also seen those growing along roadways in some places, so I don't think road pollution was a problem. In fact, I have both Leucothoe and Rhododendron growing the same distance from the road as they were planted here, but not near any black walnut. Needless to say, so far it seems juglone is mostly not an issue except in some very specific situations. Have you tested any of these species yourself, or others? What native plants did you find do not tolerate juglone? (Ps, if plants die, I do add them to the back of my sign as "not tolerant.)
