Mulching around a tree surrounded by stone concrete

(Question)

Hello we live in Toronto. We have a white Lilac tree in front of our property. It is surrounded by an~ 8×8 foot patch of grass, which is surrounded on all sides by stone or concrete. We would like to cover the grass with mulch and a stone edge. Would this harm the tree? I was advised to use blocking plastic to cover the grass, before putting down the mulch, but this seems like a bad move for the tree. How best to replace/ cover the grass with mulch? Your advice would be much appreciated!

Kind regards.

(Answer)

Thank you for contacting Toronto Master Gardeners.

There are several ways to change your lawn to a mulched area around your tree.

  • One can dig out all of the sod that is down, leaving a dirt a layer to then mulch over. If you do this you may still have weeds growing up through the mulch as disturbing the soil can cause dormant weed to sprout.
  • One can cover the grass and/or dirt with a variety of landscape covers ranging from plastics to cloth. The purpose of this layer is to block sunlight from reaching the weeds and grass. the grass will die off but you will be left with the layer remaining underneath the mulch. If you use plastic this can lead to moisture issues as it does not allow oxygen or rain to penetrate.
  • One can cover the grass with many layers of overlapping newspaper to create a mat that allows no light to the grass below. You will need at least 8 layers of newspaper to stop the light from penetrating the paper. If you dampen the newspaper as you place it down it helps keep it in place for you.Cutting the grass short before you begin also makes it easier to lay the newspaper. I extended a garden with this technique. I did not have any newspapers so I used the paper lawn bags I have for lawn waste. Over time the paper will break down along with the grass  adding nutrients to the soil.

There are many different mulches that can be used to cover an area . You have not mentioned which mulch you are hoping to use.

  • Stones as a mulch will do little to help your Lilac tree as it will not retain moisture and will heat up on hot summer days.
  • Wood mulch comes in many different styles and textures. The large chunks of bark take longer to break down and hold less moisture than the finer shredded mulches.Wood mulches serve to retain moisture in the ground as well as add an insulating layer. This supplies the tree roots with more moisture availability and a more temperature control. The tree will be less stressed and have a better chance to grow strong. You should maintain a 2 1/2 inch thick layer of mulch around the tree. The frequency you will need to replenish the mulch will depend on  how quickly your mulch  breaks down. When adding mulch ensure you leave at least a 6 inch space around your tree next to the trunk allowing air flow to get to the bark keeping it healthy and disease free. Never pile the mulch up against the bark.
You also mention that you would like to put stone around the outside edge of the space. Tree roots grow out from the trunk far past the drip line. Be aware as you place the stones that you are not damaging any roots as you dig down to set the stones.
Here is  a  site on mulching:
I hope this helps.