Okay, specific question for those who grow under and around Black Walnuts.
The guilds I build on my property have Eighty year old black walnuts as the dominant canopy. I am taking that and running with it. I use this as my primary planting guide for physical arrangements:
Black Walnut Toxicity to Plants, Humans and Horses
Richard C. Funt Jane Martin
I have some medicinals that I'm trying to "tuck in" here and there, and can't find a solid reference for Valeriana off. so I'm wondering if someone with better botanical knowledge than me knows if I can plant them under the drip line or not. They are surviving in pots in proximity, but they need to get in the ground, the heat in Central Virginia is atrocious lately (and I would love to argue what the weather stations are reporting another time...It's much hotter than reporting IMO).
Anyhow, Valerian in proximity to Black Walnuts or not??? Go!
My place has a collection of walnut trees, a couple that are upslope, then a bunch of younger ones that fan out below them. I'm going for the "try it" technique. Because if nothing else, who knows how the people who made up the lists were growing their stuff? If they fertilize, sprinkler it, etc, is that the same results as deep mulch and soil held moisture? Was the shade from the tree affecting the growth, depending on the light levels under it? Were there other plants that were helping or hindering?
In the end, there are SO many factors that can affect growth or non-growth, that experimenting with your own parameters is really most effective.
If your plants in pots are heat stressing, have you tried burying the pots? That helps a bit (not 100%, but a bit. They still want more root/water room.) Maybe bury half the pots, and plant out the other half, so if your planted ones die off, you still have stock. If they do well, pull the pots out of the others.
I know a song, (that no one else seems to) that the tag line is "why don't we try... EXPERIMENTS!!" that I often sing when I'm doing weird things to plants. I moved from the desert, where I had a lot of stuff growing that I was told "you can't grow that here!" Oh, I didn't know, so I didn't tell the plants, so they didn't know either! Microclimates are your friend....
I have 5 English walnut trees and under the canopy i grow red currants and Josta berry, a cross between black currant and gooseberry. For 7 years. They do fine. Enough fruits. Few disease. Even nasturtium grows. As Walnuts normally grow in the dry spots it would not be the best idea to grow Valeriana , witch loves wet ground. Valerian is more a plant for the wet meadows.
Let Nature work for you.
He's dead Jim. Grab his tricorder. I'll get his wallet and this tiny ad:
Soil Testing: Genius or Snapshot of the ever-changing?