Question
I'm having a dead 60 ft. cottonless cottonwood tree taken down and wonder if it's okay to use the wood chips from it as mulch?  I've been told that it might not be a good idea due to bugs possibly munching my other plants.  I live in Northern Colorado.  This tree died "very quickly" - someone told me it was due to lack of water but it's possible it may have been diseased.  A couple of years ago I 'did" have all of my trees sprayed for some kind of mites.  Any insight on using fresh untreated wood chips as mulch from this tree is greatly appreciated !
Thank you - ps.  I'm sick about this tree dying.  It provided tons of shade to my house from the west sun...

Answer
There's been some research from Virginia Tech and University of Maryland that fresh wood chips can be very acidic (sometimes down around a pH of 4) and also borrow nitrogen from the soil as the chips are decomposing. Both of those can be problems for plants trying to grow in a bed mulched with fresh chips.


Ideally, the chip pile should compost for a year and be turned at least a few times. Mixing high-nitrogen grass clippings and a little alkaline-inducing wood ashes into the pile would help counteract the acid and nitrogen issues.

Here in the real world where most people don't have the time or inclination to do the ideal, just piling it up and letting it rot for a year or two should be fine.

But consider this. The amount you use on a bed also is a key factor, so if you're only planning to put down a light layer of, say, an inch of fresh chips, that's going to have little impact on the garden's acidity level. It's pretty easy to immediately counteract any potential nitrogen problem by scattering a little lawn fertilizer (or similar high-nitrogen fertilizer) over the chips after you spread them. For that matter, you could add a light dusting of wood ashes from the fireplace or ordinary lime from the garden center to counteract any acidity trouble, if you're worried about that.

Researchers found that the effects of wood chips involve mainly the surface of the soil, which means it's mainly shallow-rooted plants like perennial and annual flowers that would run into fresh-wood-chip trouble. Deeper-rooted trees and shrubs are much less likely to be affected.

Occasionally people worry about spreading diseases from diseased branches being chipped up and used as mulch. Researchers also looked at that and found it's highly unlikely. You'd need a pathogen that's not only survived the chipping and composting, but it would have to be placed near a species it favors and have the right environmental conditions to spread and grow. The same goes for insects--insects will not survivie the chipping so will not be a problem.