Trees in urban areas face many stressors including compacted soil, temperature extremes and competition for essential resources like water. A simple but effective solution for reducing stress? Mulch!
Mulch is simply a layer of material that is applied on top of soil, but what material you choose and how you apply that material will influence the benefits your tree receives from it. Let’s explore how to get the most benefits out of your mulch to reduce stress and help your urban trees thrive.
Choosing the Right Mulch
Careful, not all mulches are created equal! For the best results, choose organic, undyed mulch materials like bark chips, wood chips and/or compost and leaves. Avoid inorganic mulch materials like rubber, plastic or fabric and any treated or dyed mulch materials.
How to Mulch Around Trees
You should aim to mulch your tree at least twice per year, typically once in spring after the ground thaws and once in fall before the ground freezes. Spread your mulch in a circle around your tree, as far out as you are willing. Ensure the mulch is no more than two to four inches deep. Keep mulch in a “doughnut” shape, leaving about six inches of space that is free from mulch around the trunk.
LEAF Tip: Avoid the dreaded “mulch volcano” around trunks as mulch holds moisture and can causes decay when piled against the trunk.
Top Five Benefits of Mulching
1. Moisture Retention – Water is crucial for maintaining tree health, but when surface soils are exposed to heat and wind, they can lose water through evaporation. Organic mulch creates a natural barrier that reduces evaporation from soil so that more water is available for roots to absorb, especially during times of drought. Mulch also holds onto moisture like a sponge, slowly releasing it back into the ground.
2. Temperature Regulation – Urban environments experience extreme temperature fluctuations throughout the year, from summer heatwaves to winter freezes. Mulch is a natural insulator that protects soils from these extreme cold and hot temperatures. The insulation also helps create more consistent soil temperatures that foster healthy root activity.
3. Weed Suppression – Weeds compete for same resources that trees need to survive and thrive like water, sunlight, and nutrients. A proper layer of organic mulch forms a physical barrier over the soil, blocking sunlight and preventing weeds from establishing. Even if some do sprout, they should be much easier to pull out with mulch!
4. Aesthetics and Physical Protection – Regularly mulching your trees not only improves their health, but also creates a tidy, well-maintained look in any yard . Mulch also reduces soil erosion and runoff while protecting the tree’s base from lawn equipment like mowers or trimmers by providing a visual and physical barrier.
5. Soil Health Improvement – As organic mulch breaks down it releases essential nutrients into the soil that can then be absorbed by tree roots. Additionally, the decomposition process supports the growth of beneficial microbes and fungi that create a healthy, balanced ecosystem in the soil.
Mulching is a simple yet effective way to give a boost to your trees. By retaining moisture, improving soil health and offering protection, mulch supports your urban trees as they grow into the canopy of tomorrow.
Jon is an ISA certified arborist and the Residential Planting Programs Senior Field Coordinator at LEAF
LEAF offers a subsidized Backyard Tree Planting Program for private property. The program is supported by the City of Toronto, the Regional Municipality of York, the City of Markham, the Town of Newmarket, the Regional Municipality of Durham, the Town of Ajax, the Township of Brock, the Municipality of Clarington, the City of Oshawa, the City of Pickering, the Township of Scugog, the Town of Whitby and Ontario Power Generation.