Did I just poison the garden? The black walnut question.

Uh-oh spaghetti-o’s! Did I destroy our garden?

The gnarly black walnut (Juglans nigra) tree in our front yard finally shed its leaves in November, a good three weeks behind schedule. I raked some of its  mustard colored leaves into the road for the city leaf pick-up and the rest went into the backyard as the first layer of the new compost pile and as mulch on a couple of the garden beds.

I didn’t think twice about it, figuring it could be incorporated into the compost and at the very least prevent the regrowth of too many weeds and grasses in the garden. Of course, not thinking twice about doing spontaneous things to your garden probably isn’t always the best decision.

A week later the cherry tree in the backyard by the garden plopped its whole sticky mess of leaves to the ground. As I raked up its sopping wet leaves it finally occurred to me *insert delayed lightbulb cartoon here* that some leaves might be better than others to compost and use in the garden. What a novel idea!

So looking for instant gratification, I perused the internet for ideas on composting my leaf haul–after the fact, of course. At first I happily found that, indeed, cherry leaves were on the Compost Gardner’s  good list!  Success! But then of course I saw the “not all leaves are created equal” part of the list. The first twinge of doubt came and while I did not see walnut on the list of not-so-good leaves, I immediately looked it up. And what I found was not very encouraging.

It turns out that not only are black walnut tree leaves not the greatest for composting, but they are poisonous, or at least they contain a poisonous chemical called jugalone (not related to the elusive, Juggalo, thankfully).  According to the WVU extension serviceplants adversely affected by being grown near black walnut trees exhibit symptoms such as foliar yellowing, wilting, and eventual death. The causal agent is a chemical called “juglone” (5 hydroxy-1, 4-napthoquinone), which occurs naturally in all parts of the black walnut”. Foliar yellowing, wilting and eventual death? That does not sound good. Not good at all.  Particularly when it is especially deadly for some of my favorite plants including tomatoes and peppers!

BUT as I crawled into the depths of a walnut despair spiral I found a little piece of hope.  The Ohio State Extension Service blurb on black walnut trees notes that black walnut leaves do contain jugalone, but in smaller amounts than other parts of the tree and that the leaves can compost effectively and become benign in 2 to 4 weeks. I do hope that they are correct and that the wet Oregon winter will effectively wash away any trace of poison. Because my plan is simply to wait and hope really hard that it all works out next year.

The jury is out on Mr. Jugalone. The leaves are too far gone to move and tomato season is a long ways out. So the test will have to wait until planting season comes. But lesson learned! It’s always good to do a little research before spontaneous garden activities!

Oh and these guys are another story altogether.

naughty squirrels...
naughty squirrels…

The giant squirrel family (many squirrels, not giant squirrels) that lives next door has probably buried hundreds if not thousands of walnuts in the garden. If the tomatoes survive the leaves, will they survive the nuts? They weren’t particularly happy last year, but I assumed it was lack of sun and inadequate nutrients. Did the walnuts take part too? Well next year we shall see. We shall see.

Does anyone have any black walnut success or failure stories they would like to share? I would love to hear if anyone else has dealt with this issue.


3 thoughts on “Did I just poison the garden? The black walnut question.

  1. Many plants produce toxic compounds to fend off competing plants from invading valuable root space.Some natural toxins are easily as toxic as man-made chemistry. The difference is their persistence in the environment. If you think about it, given the often highly-toxic natural compounds, it is surprising that there are no areas laid waste and uninhabitable by these chemicals. This shows that persistence is low, and the forest floor breakdown of leaves and plant material results in the rapid deactivation of the toxic properties here.Composting is not a natural event in itself, but does use the natural bacterial, fungal and chemical breakdown systems seen all around us. Hence composting will have the same effect on these natural toxins as if the material just rots on the forest floor. It would pay to mix large volumes of known non-toxic plant material, eg sawdust, clean grass mowings etc, to any batch of leaves that you know contain toxins. Also give it extra time to break down before using on tender food plants!


    1. Thanks for your insight, RG. I too often forget about the toxic properties competing plants can have–especially those that seem relatively benign to humans (i.e. anything not with giant thorns or poison oak/ivy/sumac). But it makes complete sense in the competitive natural world. I think the idea of mixing non-toxic organic matter with the known (potentially) toxic leaves is an excellent idea as well. I read on one of the university extension service sites that the ultimate test for deactivated jugalone is to plant a tomato start or two in the questionable areas and see what happens. I plan to follow through with something like that to test the safety of any gardening plots in question this next round. Again, thanks for the sight.


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