The application of organic mulch can greatly enhance tree health and tree longevity. Mulching is particularly important for newly planted trees.
Benefits of organic mulching:
•Retains soil moisture and reduces water evaporation from the soil surface
•Regulates soil temperatures by providing an insulating layer to protect the soil from extremes in temperatures (soils stay cooler in the summer and warmer in the winter).
•Improves soil fertility through the decomposition of the organic matter and promotes soil fauna (e.g. earth worms) and soil flora (e.g. mycorrhizae) populations
•Improves soil structure. The breakdown of the organic matter will increase the water holding capacity in sandy soils, while decreasing the bulk density (i.e. compaction) in clay soils.
•Prevents mechanical damage from lawn mowers and string trimmers (e.g. “weed-whackers”)
•Reduces soil erosion as the result of wind and water
•Reduces weed competition
•Reduces soil compaction by restricting pedestrian traffic over roots
•Adds to landscape aesthetics
Types of Mulch
Examples of organic mulches include wood chips, composted manure, cedar bark, and cocoa hulls. Inorganic mulches include river rock, pea gravel, and pulverized rubber. The problem with using inorganic materials is that they retain heat and causes the soil to dry more rapidly thereby increasing watering requirements to the roots. Additionally, inorganic mulches are typically laid over landscape fabric/ weed cloth which reduces the efficiency of water permeability to the roots.
Do’s of Mulching:
-Mulch depth should not exceed 10 cm (4 inches).
-The wider the mulch area the better. If possible, mulch to the drip line of the crown (i.e. the outer edge of the tree canopy).
-The mulch ‘ring’ should have a ‘dish’ configuration such that the sides are higher than the centre of the ring which is closest to the tree trunk. The root collar (the base of the trunk which flares out) should be exposed and not covered with mulch.
-Re-apply mulch as required as it decomposes
Don’ts of Mulching:
-Do not pile mulch against the trunk of the tree. This is a poor practice commonly referred as “volcano mulching” and only serves to shorten the life span of the tree. When excessive mulch is piled against the trunk this will encourage trunk diseases and promote root rot.
-Do not over-mulch with depths exceeding 10 cm (4 inches). This limits the tree’s ability to uptake water, nutrients, and CO2
-Do not pile soil against the trunk.