December 8, 2008
It’s fall and the trees are putting a winter blanket over their roots. In the forest the soil is covered with leaves and other decaying organic matter.
This organic mulch slowly decomposes improving soil fertility, aeration, structure, and drainage.
Mulch is part of a tree’s natural environment and provides the perfect conditions for roots. We can learn from this as the trees know how to take care of themselves.
Organic mulch provides many benefits beyond soil improvement. Mulch conserves water by decreasing evaporation and helping water soak into the ground faster. This makes more water for roots, while reducing soil erosion and runoff that contributes to flooding.
Mulch is natures blanket keeping the soil cooler in the summer and warmer in the winter. This moderation in temperature extends the season available for root growth.
Some plant diseases can be inhibited by mulch and beneficial organisms are stimulated. A 4-inch layer of mulch reduces germination and growth of weeds, in turn reducing competition for resources and yard maintenance.
Mulching around trees helps prevent trunk damage from weed-eaters and lawn mowers. All these benefits make your trees and plants grow better, and a well mulched planting area looks nicer too.
In contrast, many people rake their soil continuously in a misguided attempt to make things look clean and tidy.
Bare soil is not favorable for root growth and the environment. More water is wasted to evaporation and more runoff causes soil erosion. The top soil erodes first, and leaves compacted subsoil exposed. The temperature of bare soil experiences greater extremes, reducing root growth.
The lack of organic matter decreases beneficial organisms and favors some diseases. Ba re soil becomes a place for weeds to germinate. Continued harvesting of the organic matter depletes the soil , causes poor root growth, and unhealthy trees and plants.
There are two major types of mulch commercially available, organic and inorganic. Inorganic mulch includes cobbles, gravel, lava rock, and landscape fabrics. Inorganic mulches do not decompose and improve the soil.
For this reason, most trees and plants prefer organic mulches. I recommend only using inorganic mulches in small areas, for paths and dry creek beds.
Organic mulches include leaves, pine needles, wood chips, straw, bark, cocoa hulls, and compost. These mulches decompose at different rates.
Compost, straw, and leaves build the soil the fastest, but need to be replenished annually. Wood chips and bark decompose slowly, needing to be replenished once every three to five years. If you ask the trees, the very best mulch is their own leaves.
Mulch is good, but too much in the wrong place can be bad. In landscapes, deep mulch and poor irrigation management can cause root rot.
Mulch piled high against the trunks of trees can cause rodent, insect, and disease problems. Fine textured mulches that are too deep may become matted, preventing water penetration.
Over many years, straw and grass clippings will make the soil more alkaline, while pine needles and bark will make the soil more acidic. Most trees prefer acid soils, and if you want to grow something that likes alkaline soil you can add lime.
Mulch should be applied wide not deep. Organic mulches should be applied 2-4 inches deep and never more than 6 inches. Mulch should be kept back a few inches from tree trunks, leaving the root crown exposed.
In poorly drained sites mulch should be shallower, and in non-irrigated sites it can be deeper. The mulch should extend to the tree’s drip-line or beyond. The tree would prefer to have its entire root system mulched, which often extends three times as far as the branches.
So fall is here and we have leaves everywhere. Leaves are often called “green waste,” but should be looked at as “fall gold.” We must move the leaves from our lawns, ground covers, driveways, and decks.
Hauling leaves away, or burning them, does not improve the health of our landscapes or the environment. I like to call fall “leaf relocation season.” Use the leaves to cover up bare dirt, smother out weeds, mulch your trees or make compost.
If you must haul the leaves away, you will have to bring back an equal amount of your favorite organic mulch to maintain a healthy landscape.
For healthy trees, leave the leaves.
Aero Acton is owner of Leaf It To Me tree service.