Hi Jennifer,
I found a good site with the info you're looking for - it's not good. It says that the toxicity can last for years as the dead roots are still releasing juglone. I'm adding another address that had some rather startling info on the root/toxicity zone. It was a lot larger than I thought. That would be in the Ohio link here:
http://ohioline.osu.edu/hyg-fact/1000/1148.html

Hope this helps and wish the news was a bit better,
Ginger

Here is a link that might be useful: Black Walnut Toxicity

If your husband is willing to cut it down for you - do it!
And then plant 1 or 2 squirrel friendly trees in its place - such as Oak or Horsechestnut.

Our yard is surrounded by huge BW trees, so I understand your frustration. Even more frustrating is seeing little trees planted by squirrels, sprouting just beyond our fence in our neighbors yard, and they aren't removing them. Soon our yard will be a complete network of BW roots.
If you remove all your BW trees, you are reducing the odds of more trees appearing in the future at the other end of your lot which is currently juglone free.

I too have read that the juglone can persist for many yrs after a tree is removed, but if you plant only tolerant plants now, eventually you can work in others. Time flies so fast - before you know it 5 yrs will have passed!

If you leave the remaining tree, the roots will eventually travel much further than 25 ft. - this spring I found many pencil-sized roots just 6" below the surface from a neighbors tree >60' away. Cornell Univ found roots can grow 3 times the spread of the canopy.

I had planted yews in an area I thought was safe - they did great for years til 2 started dying, & I found walnuts buried inches from their trunks. So last fall I dug-out a whole row of 3' yews.

Black Walnuts are beautiful trees & serve an important role in nature, but they don't belong in a garden or small yard - they belong in large open areas. There are so many more suitable trees available - why leave a tree to grow that you will resent for all the years you live at this house?

And I haven't found any annuals that flourish under a BW.

You should really talk to a sawmill before you take down a large black walnut.... they can be worth quite a bit of money if you take them down the right way (and don't chop em all up to hell).

Jennifer, if you're still using this forum I'd love to know how your garden is doing post BW. An ill-informed landscaper just planted azaleas, rhododendrons, viburnums and hydrangeas under our BWs... some of the plants most susceptible to juglone! Argh!

I am planning to take the trees down soon and wondering if the plants might eventually recover as the poison dissipates. Have you had any luck planting things sensitive to juglone yet?

Perhaps I need to repeat. I took down several large black walnuts and the juglone does not persist any time at all.

@laceyvail, I appreciate hearing about your experience, but it is anecdotal. If the poison is present in the roots as well as mulch from grinding stumps, it doesn't make sense to me that it is POOF gone immediately. It would logically break down in the soil for some time. Also, your post is about how plans faired the following year...

I would love to hear from anyone who's had experience with intolerant plants that were planted just before or after the walnuts were removed. Thanks!

@georgeannaco- I have been growing viburnums and/or hydrangeas under a BW for 25 years without issue. A native viburnum seeded itself 5 feet from a 50 foot BW 25 years ago and is quite happy. As for juglone in the roots, the amount is small compared to the leaves and bark and I find the fibrous roots to be more of an issue than the juglone they contain. Therefore, as laceyvail said, once cut down a BW's roots become moot. For the record, I've seen studies indicating it may persist for a year and by the end of that year only trace amounts remain but remember, there was not much there to begin with.

tj

Studies also showed an interesting correlation between good drainage and lesser concentrations of juglone in the soil. There are even microorganisms that nullify or breakdown juglone and soil components that interfere with the toxicity. Every situation is different, so there's no concrete answer to be had.

There will always be someone with the 'special' tree, shrub, location, etc, where something does well and it shouldn't; usually there's an attribute that will explain it. The walnut that has such a great stand of vegetation beneath it that I've observed has a heck of a terrific situation for drainage. Heavy organic matter added to the soil probably helps there as well.

Thank you @tsugajunkie z5 SE WI and @ging(7a)! I have laurels, rhodos, azaleas & hydrangeas that were planted under the trees. So far the hydrangeas are happy and the others are "sleeping." Here's hoping they creep next year and leap the third!

Of the four you listed I'd fear for the rhodos and azaleas most. I have no experience with laurels and BW but I killed a rhodo within months of planting it in a bed amended with BW leaves and then I mulched the plants with BW leaves. Hey, that was 30 years ago, what did I know? There was no internet to ask.

tj

After extracting the 'meat'(kernel) from the shell of the Black Walnut, there is alot of debris(from the shell) mixed in with the precious 'meat'.

Previously, visually. . .I carefully removed 3-5 small slivers of shell from about 1/2 cup of Black Walnut 'meat'.

An old Cherokee trick is to place the 1/2 cup of Black Walnut 'meat' in a pot of warm water and the lighter 'meat' will rise to the surface while the heavier shell-slivers will sink. Works!

True, the shell-slivers were accompanied by the huge pieces of 'meat'. However, that was fine since we are looking at 2-3 really-really large kernels. Using a strainer I can easily remove all the light 'meat'(kernels).

As one person said, every situation is different. I had a reasonably young yet strong BW removed a year ago and the stump was ground out 12” below the soil. However, I’ve been dealing with BW suckers popping up from the roots all summer long. Clearly the roots are still alive. Living roots are still producing juglone.