mulch versus plastic with river rock

Asked April 6, 2016, 1:06 PM EDT

A few years ago we replaced mulch around our town home development trees with plastic and river rock, so that the mulch wouldn't have to be replaced every few years. Because of a different issue, our property manager had a couple of arborists review our situation. They relayed to our manager that the river rock should be replaced with mulch. Is using plastic and river rock detrimental to the health of Linden trees? It was also stated that our soil was very compacted. Our soil is very sandy. Is it likely it would encounter a compaction problem?

Wright County Minnesota

1 Response

The arborists are absolutely right. Black plastic should never be used under mulch. It prevents water from reaching critical root zones. This is especially true of trees which have roots that spread at least as far as the canopy.

Odd as it may seem, sandy soil can become compacted. It is important to amend planting areas with compost to improve water-holding capacity and air in the soil. Tilling in the compost well to ensure it is mixed with the existing soil.

Rock such as river rock is an acceptable mulch. It should be installed with water-permeable landscape fabric underneath it to prevent the rock from working its way into the soil. It is also easier to remove rock in the future if fabric has been used.

Here are a series of Extension publications on soils and composting that may be helpful:

Tree publications including information about planting and caring for trees can be found here: