Walnut shells

Hi -- Years ago it was believed that crushed walnut shells poison the soil for garden plants. Is this still the prevailing wisdom? Have an abundance of shells from a gift box of walnuts received from CA. Seems wrong to just toss in the garbage. Always thought what came from the ground should be returned to the ground, but I don't want to hinder the growth of my garden plants. TIA (Z6,NJ)
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You shouldn't have anything to worry about. Black walnuts, as do a number of other members of the genus, excrete a hormone - primarily from the roots - which can hinder the growth of sensitive plants. English walnuts possess this hormone in much lower concentrations and even less so through the shell. And how large a gift box are we taking about ? It can't be too many shells to begin with. If you have any concerns, use them for informal pathways.
pam - gardengal
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You are suggesting a hormone that would suppress weed seed from germinating?
That sounds like a good thing, doesn't it?

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Gee, Twitbetold. For someone from New Jersey you ask a lot of stupid questions.
There is no problem using walnut shells as mulch providing you do a thorough job of pulverizing them!!! So get yourself a hammer and smash the crap out of them. Its good stress relieving therapy for the holiday season too.

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Use of Waste Products Synthetic mixes may use organic ingredients that once were classed as waste products - conifer bark and redwood sawdust. Although these particular ingredients have been thoroughly tested for toxicity, pH reaction and uniformity, other waste products also can be used."What comes out of the soil should go back into the soil," say conservationists, but gardeners do not always agree. While it is true that crushed almond shells, as well as grape pomace (when composted) can be used safely as a soil amendment, walnut leaves or crushed walnut shells poison the soil for garden plants. Sunflower seed hulls look promising, but tests have proven that they contain some growth-inhibiting properties. Any organic material, especially agricultural by-products, must be tested carefully to ensure that it contains no toxic elements. Resource: The American Horticulture Society Illustrated Encyclopedia of Gardening 1981 March 1991    Chemung March 2000    Revised
Hi Pam -- Above is from Cornell site citing AHS's encyclopedia, but it's from 1981. Thanks for your reply, helpful as always. It was a 20 lb. box. I guess the quantity of the left over shells would appear different to different people. Thanks again
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I'd say that quote was a little simplistic at best. Allelopathy is common to a great many plants, but in varying degrees and most often, affecting only certain target plants. To say that walnuts "poison the soil for other plants" is a bit of a misstatement. The hormone that walnuts - and primarily black walnuts, Juglans nigra - excrete is concentrated in the root system and can inhibit the growth of only certain plants. Concentrations in leaves and shells are significantly lower. And since the effect is limited to only certain plants, primarily those in the Solanaceae, it can hardly be said to "poison" the soil. English walnuts, Juglans regia, possess juglone in a much lower concentration, so the effect will be even slighter.
And a 20 lb box is not enough shells to worry about, regardless. I use hazelnut shells on my pathways and a 50 lb sack of those is just a drop in the bucket - it hardly covers anything.
pam - gardengal
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