Question
We live in southern Utah - it's pretty much a desert, so there's not a lot of green around.  We have planted three Mondell Pine Trees in a row by each other and surrounded the base of all three with lava rock.  After three years, we are now in the process of removing the lava rock to put wood chips down in its place.  However, getting rid of all of the lava rocks is a tough process, coupled with the fact that there is a layer of plastic underneath the rock that leads right up to the base of each of the trees that serves as a weed block.  Our question is this: Is lava rock detrimental to Mondell pine trees?  That is, if we are unable to remove 100% of the lava rock, is it okay to mingle wood chips and lava rocks together to serve as a base mulch?  In the process, is it a good idea to remove the plastic in order to give the trees some breathing room, or are the pines going to get the necessary nutrients/breathing space they require if the plastic is left on top of the soil?

Answer
Jared,

Leaving the lava rock will be ok. It's not particularly reactive with anything.  Having it there will just be a matter of looks.

But, your instincts are right about the black plastic.
Get it out of there!  That stuff can really mess up root development, even of large trees.   

If wood chips are what you want down there, keep an eye on the trees over the next year for yellowing.  When chips break down, the bacteria that do the work use nitrogen.  It's not unusual for that breakdown process to  tie up a lot of nitrogen, depriving the plant you're interested in.

Mark in Portland