Question
During a recent storm, we lost several old pines (uprooted). We are trying to avoid having to burn them. Can we put them thru a chipper and use them as mulch? I have heard "Yes" and "No" from friends...time to check with an expert. Thank you.

Answer
Yes.
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.