Since it's on top of the soil as opposed to mixed in it and only a low percentage of the total mix, I honestly wouldn't worry about it. Others may disagree but I think any damage done would be very minimal - if any.

You could, if you wish, just rake it back from the base of the roses, etc. a couple of inches. Leave a 4-5" clear ring of exposed soil around their bases for a couple of months until it all begins to decompose and then rake it back up to the plants.

Hope this helps.

Dave

I've gotten away with a small percentage of walnut wood (and also norway maple wood) in my mulch. It might also matter what you are trying to grow. I have some rhodos and azaleas growing under one walnut tree and bloodroot growing under another and they are all doing fine. You could try cross-referencing walnut and juglone against your plants to see if they are particularly susceptible or resistant. Digdirt's advice sounds right to me.

I have had the Black Walnut wood chips mixed in with most all of the wood chip mulch I've used and have seen no problem with it. Since a Black Walnut is trying to keep other plants from growing nearby, so they will not "steal" the food the Black Walnut wants, most all of the Juglone is in the roots of the tree. I have really not seen any detrimental affects from using with the chipped wood or shredded leaves from my Black Walnut.

Allelopathic chemicals are found in the leaves, in run-off from the branches, from the bark, as well as the roots. Just so you know.

However...I, too, think that you have little to worry about at this time.

Not to worry. The juglone breaks down in about a year just by being exposed to the air. Since this happened in December and its on the surface and a small percentage of the total mulch I wouldn't worry. I still might keep it from tomatoes, though.

tj