Compost Placement and Drip Line Determination For European Beech Tree in West End Toronto


In this link, the City of Toronto recommends using the drip line for composting/mulching, but I don’t understand how close to the actual West End Toronto tree trunk I should be, since it suggests going to the edge of the drip line. But how close should the compost be to the trunk?
In this link, your suggestion is about 2-5 cm from the tree trunk.
Did I get too close to the 9 year old European Beech tree trunk? I thought the grass will grow to the perimeter, since the tree took so much of the lawn away, before it was so aggressively pruned. I can pull the compost closer to the edge if that’s healthier, but I’m afraid crabgrass might be all that will grown in, given the lighter rainfall. It might look better too if I pull the compost out further. What do you think?


Thank you for contacting Toronto Master Gardeners.

Correct placement of compost and mulch under trees is an important topic. You have found some useful information online. A tree drip line is as wide as its canopy. The Twitter link you posted -from the City of Toronto Forestry department, has a good illustration showing the edge of the canopy. I can see from your photo that your compost or mulch ring does not go out as far as the widest branches of your tree. You could take the mulch out further. With larger trees you can end up with a very large mulched area- which may not work with your garden plans.

The key point is that the area along the ground, from the trees trunk to the edge of the drip line, is the most active for absorbing water and nutrients- essential for the trees growth and health. As your mulch decomposes over time it will release nutrients into the soil. Having a layer of mulch a minimum of 5cm thick also absorbs water which is then taken up by the tree. Beeches are fairly shallow rooted, so having a layer of mulch helps to protect the roots from drying out over the hot summer months.

Even if the mulch doesn’t extend to the edge of the drip line, the amount you have put down will help. From the photo it appears that your canopy is about 2 ft wider than your mulch on the sides parallel with the driveways on your street- so you could extend the mulch another foot or two at these sides. Drip lines aren’t always circular. Yours appears to be oval shaped.

As per your Toronto Master Gardeners link, leaving a 2-5cm space between the trunk and the mulch is important to prevent the trunk from rotting or attracting fungal diseases. The space you have left gives the trunk plenty of clearance, so no need to move it.

I can’t tell from your attached image whether you have added mulch or compost at the base of your tree. The Toronto Master Gardener link you posted describes the difference between the two. If you have applied compost, you can add shredded cedar mulch over the top, about 5 cm thick. The compost will give your tree an extra nutrient boost, and the mulch will hold the compost in place and slow down the water evaporation rate.

Your tree will enjoy the extra moisture and nutrients.

Aug 1, 2021