From the Ohio State University extension service.

Horses may be affected by black walnut chips or sawdust when they are used for bedding material. Close association with walnut trees while pollen is being shed (typically in May) also produce allergic symptoms in both horses and humans. The juglone toxin occurs in the leaves, bark and wood of walnut, but these contain lower concentrations than in the roots. Juglone is poorly soluble in water and does not move very far in the soil.

Walnut leaves can be composted because the toxin breaks down when exposed to air, water and bacteria. The toxic effect can be degraded in two to four weeks. In soil, breakdown may take up to two months. Black walnut leaves may be composted separately, and the finished compost tested for toxicity by planting tomato seedlings in it. Sawdust mulch, fresh sawdust or chips from street tree prunings from black walnut are not suggested for plants sensitive to juglone, such as blueberry or other plants that are sensitive to juglone. However, composting of bark for a minimum of six months provides a safe mulch even for plants sensitive to juglone.

Link below.

Steve

Here is a link that might be useful: Black Walnut toxitity to Plants, Humans and Horses

Living with more than a few black walnut trees under which I must garden, I can testify that most native plants are not sensitive to black walnut. Which does include certain weeds: plantains, chickweed, henbit, shepherd's purse, dandelions, goldenrod, many more. Hostas seem to tolerate them, even like them. The Springfield, Mo botanical garden's hosta garden is thriving in a black walnut grove.

There are, however, many plants that will not tolerate them at all, and vegetable gardens do not do at all well within the spread of a black walnut's roots.

There are lists on Gardenweb in other forums, it is worth a search. Sometimes you may just have to experiment. But I have found that there is a wide range of plants you can grow.

Sandy

Living with more than a few black walnut trees under which I must garden, I can testify that most native plants are not sensitive to black walnut. Which does include certain weeds: plantains, chickweed, henbit, shepherd's purse, dandelions, goldenrod, many more. Hostas seem to tolerate them, even like them. The Springfield, Mo botanical garden's hosta garden is thriving in a black walnut grove.

There are, however, many plants that will not tolerate them at all, and vegetable gardens do not do at all well within the spread of a black walnut's roots.

There are lists on Gardenweb in other forums, it is worth a search. Sometimes you may just have to experiment. But I have found that there is a wide range of plants you can grow.

Sandy

Hi Sandy. If my only experience with hosta gardens exposed to juglone were in the Ozarks I would be less enthusiastic. You are in the same type of terrain where a few inches down there is hardpan. So drainage is terrible. But washoff is significant. The juglone seems to wash out of the soil well. But not enough for iintolerant plants to survive well.

I'd grown to 'hate' the black walnut trees; until I fouind my beloved hostas seemed to love them. With the leg injury Les had last year I have become more and more active again with hostas.

Steve: I have seen the same 'test' for toxicity by planting tomato seedlings,and am not in disagreement. But the results don't seem to have much meaning if I plan to have only tolerant plants. In 'Theresa's Angel Garden' dandelions do germinate but are weak rooted and easily killed with a shuffle hoe. It is not necessary to dig out the tap root to kill them. Chickweed doesn't germinate,or if it does it never gets beyond the 4 leaf stage. Plantain and clover is all around but no where near the bw. Even voles seem to avoid the area.

In the Ozarks I believe that voles are not a problem because of the hardpan. In Illinois where I live the soil is not heavy clay and instead of sand there is a lot of coal dust. The soil drains well-excellent to be honest. Away from the bw there is a bad vole problem. Under the bw not much of one.

So I am taking the position that, as a hosta lover, I have to take exception to the commonly acceopted attitude that black walnut trees and waste are evil. Of course, having never 'harvested' the roots I cannot comment.

I no longer feel a need to police the area under a bw for the dead leaves, wands, or walnut husks that squirrels drop. I would rather grow hostas under a bw than ANY maple.

I haven't found bw to create dense shade either. In the spring the 'wands' create wispy open shade and in early fall the bw drops it's leaves early. This is a great condition for hostas.

I am not a spring chicken and last year couldn't keep up with my brothers gardens in the early, record setting heat and drought. But eventually, together, we overcame the weak weed onslaught. In his maple garden things didn't fare so well, and hostas were lost.

Black Walnuts, as trees are lovely. Their fronds blow gracefully in the slightest breeze admitting brief sunrays, and their light green color is very pleasing to the eye.

They are similarto the gorgeous snow I am now viewing out of my window. It isn't the snow I curse, but the plow driver who always plows it in the same direction so in the morning I will have to level a 3-4 foot pile blocking my driveway while across the street there is nothing.

I am a strong woman, but am still a woman and moving 4 feet of wet snow is very hard on me. I tend to cry in frustration, but I have determination to perservere. A snow plown driver can't beat me down, even when i am in my 70's. LOL

I have so missed the winter wonderland I now see out my window.

Theresa

From the information you all are providing and your firsthand experience of growing hostas under black walnut trees, I stand corrected. I think the only question left is if you would want to grow any other companion plants among your hostas that are intolerant to juglone. If so, you may want to avoid mulching with black walnut chips and bark. On the other hand, if you are satisfied with the companion plants that will tolerate the juglone, the black walnut mulch may actually be the preferred material.

i have to admit.. my eyes glazed over ...

kudos on your amazing research ...

but all i ask.. when speaking about a MULCH ... is how much active ingredient can be accumulated when applying a 2 inch cover over the soil ....

one might suggest ... that there is no way.. you could create a situation to get enough of the bad stuff.. to have a cumulative effect ...

COMPOST on the other hand.. say building a pile 8 feet all.. and letting it rot in place.. one might see the cumulative effect of the bulk ... as compared to the layer ...

it is often said.. that pine needles are acidic ... and i often say so what.. pH being an exponential function.. would require hundreds of feet of mulch.. over decades.. to make a minor change of the pH at surface level ... [as an example] .....

sooo.. when applying a MULCH ... which by definition.. is a soil covering.. i simply cant see that it can have any real noticeable effect ... but that is my gut speaking.. and frankly.. it lies to me once in a while.. lol ...

ken

don r: again I suggest that before using it one obtains on-line a couple of good lists by colleges etc. of juglone insensitive plants. Even then if you aren't sure you might try a small test section. In general many of the plants we use as companions to hostas are on the tolerant list. I type this with tongue in cheek but since our companion plants are shade tolerant perhaps it is their long history as under canopy existence. There are a few other trees that
produce juglone. The black walnut just has the more powerful.

The tomato plant test Steve spoke of I'd seen as advice for people who compost bw leaves for amending soil for intolerant plants, They do stress the compost pile needs to heat up, since compost won't heat without oxygen and I think they are saying the oxygen speeds up the breakdown of the juglone. May it oxidizes it, in which case the heat will probably be a catalyst. (Are there any chemists lurking?)

Theresa
Ken, I was typing while you were posting so I didn't see it until ater I'd posted. Thanks for the kudos.:o)
Actually, the greatest researcher I know that is a regular here at gwhf is moc! She is awesome.
'T'

This post was edited by gogirlterri on Wed, Mar 6, 13 at 8:26

Here's a good link, with a fairly extensive list. Very helpful. It also explains the breakdown of juglone in composted materials.

Most acids in plant material are broken down by microbes in the compost, and usually results in pretty neutral or even slightly alkaline compost, even in oak leaves. It really isn't true that oak leaves make your soil acid.

Sandy

(Edit) I see narcissus is on the intolerant list, however I have large populations of daffodils and narcissus under walnut trees that are flourishing, and have been for many years.

Here is a link that might be useful: black walnut list

This post was edited by mosswitch on Wed, Mar 6, 13 at 8:42

It seems from this research that Black Walnut compost may not be benign.

"Since ancient times, scholars have suspected that walnuts have harmful effects on nearby plants. In the 1880s, scientists isolated a compound called juglone from the fruit of walnuts. They demonstrated that injury and sometimes death result when this phytotoxic material interacts with susceptible plants.

In addition to the fruit, juglone has also been found in the leaves, branches, and roots. The actual concentration in each part varies with the season. In spring, juglone is concentrated in the rapidly growing leaves. The amount of juglone in the roots remains relatively high throughout the summer. The concentration of juglone in the hulls of the fruit increases as the crop matures. All species of the walnut family produce juglone. Black walnuts have the highest concentrations. Relatively small amounts are found in butternut, hickory, and pecan. Most toxicity problems are caused by the black walnut.

"The sources of juglone in the soil include both living and decaying plant material. Rain droplets leach juglone from the buds, leaves, and twigs. The decomposition of plant debris by soil microorganisms also releases juglone. Living roots exude juglone into the surrounding soil." "

I also read somewhere recently that coffee grounds are another source of juglone...a little OT....as you may have come to expect.

Jon

Here is a link that might be useful: Juglone data, Univ of Nebraska

Not only black walnut, but hackberry is somewhat alleopathic. Don't know offhand what the substance is in it, but there are a variety of plants that won't grow under them.

Sandy

jon-you frame your comments in quotations, but don't specify who or what you are quoting. From what Steve and I have pointed out bw compost certainly is not benign to all plants, and can be rendered benign through appropriate composting practices. What is the point you are making?

Sandy-many lists I have found show daffodils as tolerant, and I have also grown them successfully under bw. I plead ignorance in knowing the difference between daffodils and narcissus.

I have also found lists that show that melons and squash can be grown under bw and that the fruits are not toxic to humans or animals. It seems the toxic juglone is not stored in the fruit or plant matter other than the bw debris itself. I will say that even the slightest trace of juglone spells death to tomatoes and peppers. I have grown Canna under bw.

Most of the toxicisity of juglone, in the reports I have found comes from the roots and extend outward 1-1/2 times the height of the tree. So a 60 foot high bw intoxifies the soil in a 90 foot diamater circle from the trunk - roughly. This results in an area where many shade intolerant plants can exist.. That is why I made the comment that 'fringe' areas of a hosta bed under a bw can be useful for companion plants.

My daylillies have done wonderful under bw, and the trees, in my humble opinion, are almost perfect 'dappled-shade' because of the lacy texture of the leafy fronds. The area under a bw is definitely NOT deep shade. Even the gentlest breeze allows direct sun to penetrate but not dominate.

I have only gardened under bw, not intentionally used bw waste for mulch or compost. As Ken has pointed out, and the sources I have found support, leaching of juglone from surface debris doesn't penetrate far into the soil, but far enough to be toxic to seedlings of shallow rooted weeds and the plants themselves with shallow root systems such as tomatoes and peppers. The deep toxicity in soil comes from the bw root system.

So to me, I don't have a fear of the thought of using surface applied bw debris as mulch or in composted applications for juglone tolerant plants.
Theresa

Theresa, there is actually no difference. The botanical name is narcissus, and they are all narcissus but common usage has the larger flowers as daffodils and some of the smaller, older varieties are called narcissus. Poeticus, for example.

There are actually 13 divisions of narcissus, and some are classified as narcissus, jonquils, or daffodils. Confusing, huh.

Sandy

"Jon-you frame your comments in quotations, but don't specify who or what you are quoting." -by gogirlterri

I did have a link to the quoted source which is the University of Nebraska. Perhaps you didn't get that far.

My point was ""The sources of juglone in the soil include both living and decaying plant material. Rain droplets leach juglone from the buds, leaves, and twigs. The decomposition of plant debris by soil microorganisms also releases juglone."
which I prefaced by saying "It seems from this research that Black Walnut compost may not be benign."

I thought my first statement spelled out the point I would try to make. The quote did have other information which I thought was interesting. I assume this additional information didn't allow a direct enough connection to make the connection to the premise I first stated. I probably should have mentioned the link in my text as well.

The study by the University of Nebraska states that the affected zone is 2 to 3 times the drip line diameter. The larger concentrations are, quite naturally, in the drip zone.

Jon

ok-gotcha!
I have seen several sources that favor the 1.5x the drip line diameter, but some may actually be reflecting the same source. I will say that I have very successfully grown tomatoes and peppers near the 1.5x zone. This is a generallization, jon, because soil drainage vs runoff is mentioned by most garden extension reports I have read. How much surface debris is cleaned up also would increase or decrease the amount of juglone.

Have you found a report that indicates how far out from the trunk the root system extends. Surely not 3x the drip line, I would think. I have no idea. My experience gardening under a black walnut is that by about 5 feet from the trunk I have never dug deep enough to find the trees roots. The bw is supposed to have an extensive root system, but is deep rooted. IYO, wouldn't that suggest that the 3x toxic zone is more from drainoff and surface debris in poorly draining soil?

Regardless, with hostas being shallow rooted, and not subject to juglone toxicity, I can't see where the juglone, whether it be from living roots, root chips, leaves dead ir alive, nut husks or twigs need be an issue, except for certain companion plants in our hosta beds.

Is there such a thing as the black-nosed squirrel? Sure is! Every red or grey squirrel during ripened walnut season. They won't eat the hulls but have to tear it away to get to the nut. The ground under a walnut tree is virtually covered with bits of the torn off hulls which are rich with juglone.

Theresa