Mulching practices that lead to healthy trees and shrubs begin with knowing how much mulch to use, types of biodegradable mulches available, and reasons why landscape mulching is beneficial. Uneducated and detrimental mulching practices lead to diseased and dying trees and shrubs.
“All things in moderation should be a homeowner’s mulching motto,” says Jim Skiera, Executive Director of the International Society of Arboriculture (ISA). “As beneficial as mulch is, too much can be harmful in more ways than one.”
Amounts of Mulch to Use
- Apply 2 to 4″ of mulch in well-drained areas, say arborists including members of ISA. Use a thinner layer if using finely textured mulch material or there are drainage problems.
- Keep mulch away from tree trunks or shrub crowns. Recommended distances are 2 to 3″ for small trees and shrubs, and 6″ or more for large trees. Do not cover the root flare (Photo #1) – transition zone between the main stem and the root system.
- Remove any mulch that is already piled against crowns (Photo #2), stems (Photo #3) or tree trunks (Photo #4). Expose several inches of soil out from the crown, base of trunk or root flare.
- Check depth of existing mulch. Do not add more mulch if a layer 2 to 4″ is in place. Instead, rake out old mulch and remove to compost pile, or break up matted layers to restore fresh appearance.
Types of Biodegradable Mulches
- Use biodegradable mulches such as double- or triple-shredded blends of well-aerated and partially composted leaves, bark, and wood to improve soil.
- Uncomposted or raw wood chips yield sour-smelling mulch that promotes unsightly organisms such as “dog-vomit” slime molds (Fuligo spp.) and “common stinkhorn” mushrooms (Phallus impudicus). This kind of mulch material may also tie up soil nitrogen as well as change soil pH.
- Peat moss and cypress chips are not good choices because they are difficult to wet once they dry out and may restrict water movement into the soil, writes Edward F. Gilman, University of FL Professor and Laura Sadowski, Information Specialist, FL Institute of Food and Agricultural Sciences in Planting and Establishing Trees, Ch. 11, September 2007.
Benefits of Landscape Mulches
- Fine, absorbing tree roots essential for taking up water and minerals are located within inches of the soil surface, says Skiera. They extend out a significant distance from the trunk and require oxygen to survive. A thin layer of mulch, applied where these roots grow, can improve oxygen levels, soil structure, temperature, and moisture availability.
- Mulch reduces turf grass and weed growth that compete with landscape plants for nutrients and moisture. It also prevents plant injury from string trimmers, lawn mowers and other equipment.
- Suitable mulches, applied with care, can tie together and enhance woody plants in garden landscapes. (Photo #5)