On most lists Hosta is listed as juglone tolerant and columbine as jusglone susceptible. So even by a living walnut the hosta would have a good chance. (I say chance because these lists are all derived from not very well characterized observations.)

As for your Walnut trunk my guess is that it won't be a problem if it's been more than a few years since it was alive. But you can test it. Tomatoes are extremely susceptible to juglone. Plant a tomatoe plant where you want to put your columbines. If they survive your columbines should.

-Helen

Jugalone is primarily in the leaves IIRC so you should be in the clear. Any broad leaf weeds grow near the old stump?

Helen, we cut down the trunk over 15 years ago and it was rotted out prior to that. It has a very beautiful texture as part had been where a limb grew.

Brendan, until I pulled them out, yes, there were broadleaf weeds growing around the trunk.

Thank you both for your responses. I guess nothing to do now but plant them. I have to plant near a rock or some sort of hard surface or my wonderful old Great Pyrenees will think I'm making him another bed. As effective as he is at keeping deer and 2- and 4-legged coyotes at bay, he can sleep where he wishes.

We have columbine and hostas under our living black walnuts. They do just fine. I know the columbine isn't supposed to(I planted them there before I understood about black walnuts), but they are fine, after 3 summers.

Well, it's done. The columbines never missed a beat after I transplanted them--Thanks to you all.