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Joined: Tue Dec 09, 2008 12:46 pm
Posts: 5
Location: Kansas
Post Mulch
I would like your comments about hardwood mulch. Yes or No and what do you know about suitability around apple and pear trees. I have access to some harwood mulch. It's a combination of hedge, cedar, elm, and walnut. My question is about the walnut. I know about walnut toxcity in the root system but any idea about leaves and hardwood? Thank you, Michael.

Wed Aug 12, 2009 3:49 pm

Joined: Wed Sep 08, 2004 8:14 pm
Posts: 197
Location: Aurora, Oregon
Post Re: Mulch
Chipped (using a hammermill) tree prunings work well. The ramial wood (twigs and green shoots) and leaves give enough nitrogen that the chips don't take nitrogen from the soil. The mix of chip sizes keeps the material from breaking down too fast, so it lasts a couple of years. If you think there is something toxic in it, pile the chipped material and it usually heats up and composts well. It works great on trees and grapes. Just leave a few inches of space around the trunk to prevent rodents from snuggling up to the tree.

Wed Aug 12, 2009 9:49 pm
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Joined: Sun May 15, 2005 10:57 am
Posts: 1406
Location: Portland, OR
Post Re: Mulch
If the walnut is black walnut, it could give out chemicals that make things not want to grow in it.

Otherwise, I am very pro mulch. If you want to kill broadleaf weeds or grass, put newspaper down first, then mulch over it. The weeds don't get any light so they can t grow. The mulch keeps the newspaper in place.

Right as rainy season is starting is a great time to get going with that.
john S

Wed Aug 12, 2009 11:43 pm

Joined: Mon Feb 23, 2009 7:24 pm
Posts: 83
Location: Sublimity, OR
Post Re: Mulch
The heartwood, bark, seed husks and sometimes the leaves of naturally decay resistant woods contains various chemicals that are protect the woods from fungi; and in some cases will retard the growth of other plants (biocidal [sp?]). The effectiveness of these chemicals is significant and are such that for millenia continue to remain toxic to fungi.

Juglone, the extractive chemical from black walnut, ". . . can cause blackening, blistering and peeling of skin; is a tranquilizer and sedative; has antitumor activity; is fungitoxic; and is allelopathic." (Source -- Extractives in Eastern Hardwoods USDA Forest Service Forest Products Lab General Techinical Report FPL 18). Thuja plicines, in Western red cedar heartwood are similarly fungi/biotoxic. The extractive chemicals in Port Orford cedar are linked to liver cancer in sawmill workers processing that species.

Wood chip mulches are extremely effective in controlling weed growth and in helping to retain soil moisture. I would however recommend you compost wood chips that include material from naturally decay resistant species for at least one winter and not use it before next spring. Give the rains a chance to rinse away some of these chemicals and then I would test the mulch before applying large amounts to all your trees.

Wood Technologist
MS Penn State '79

Fri Aug 14, 2009 3:44 pm
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