How to Mulch Trees the Right Way
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We all have our soap box issues. They can range from the little things that just get under our skin to major life changing concerns. Lately for me my horticulture soap box issue has been tree mulching, or should I say the horrific practices I see that have been heaped upon helpless trees in our landscapes. It just slays me that people can mess up something so simple so badly!
Value of tree mulching
Creating a mulch ring around a newly planted or young tree less than 10 years old is the single best practice that can be done once the tree is planted. Tree mulching provides so many benefits, most importantly increased growth. Everyone wants a fast growing tree and proper mulching is the key. Research has proven that, over time, a mulch ring placed 3 to 6 feet around the tree can almost double the growth rate of the tree.
Mulching decreases competition from the grass. Grass robs water and nutrients from the tree’s root development and delays its establishment. A properly placed mulch ring helps conserve moisture and cools the soil aiding in root growth. Lastly, the other main advantage to mulch is it keeps our lawn mowers and weed whips away from the tender trunks. It is amazing how many landscape trees have been compromised by having chunks of bark knocked off in our zest to whack back every single blade of grass.
How not to mulch a tree 
Unfortunately you can look on just about every street corner and see examples of what not to do. Tree mulching is not heaping piles of mulch up and around the trunk. Mulching is not developing a volcanic cone of wood mulch a foot or more high right up against the trunk. I have no idea why anyone would think placing piles of mulch up next to the trunk could be beneficial to the tree.
Mulch heaped onto the trunk of the tree will result in a shortened life expectancy, or even death. Mulch that touches the trunk is moist from rainfall and irrigation. Over time this moisture rots and decays the bark layer of the tree, which kills the cambium layer area of tree growth and eventually rots the heartwood of the tree.
Deep piles of mulch, over 4 to 6 inches deep also excludes oxygen from the soil. This results in root development up into the mulch layer, not down into the soil. These so called surface or mulch roots do little to support the tree in the long-term for robust growth.
How to mulch a tree 
I have always said when it comes to mulching trees think about donuts and bagels. What is in the center of these breakfast foods? A hole! This hole in the center is where the tree trunk would be located. Proper tree mulching starts out about 3 to 6 inches from the trunk and continues out in all directions at least 3 feet. Six feet would be even better for long-term establishment and increased growth.
The thickness of the mulch layer should be somewhere between 2 and 4 inches deep, or thick. It does not take piles to accomplish the benefits of mulch. A properly mulched tree should appear to have just a slightly raised ring around the tree.
Over time the mulch will blow up next to the trunk and breakdown. This means that as part of normal maintenance the mulch ring should be replenished yearly. Start by carefully pulling the mulch back from the trunk, and then add enough new mulch to the 4 inch depth.
Types of mulch
The best mulch for trees is organic wood chips. There are a number of different wood chip products which all accomplish the desired outcome of improved tree growth. Select which type of mulch fits your budget and desired appearance. Raked leaves are just as effective as the trendiest designer dyed mulch on the market. Wood mulches will not transmit insect and diseases to the tree. Any harm associated with wood chips comes from improper mulching practices. Keep in mind, mulch serves a function. Its secondary aesthetics is only important to one’s personal taste. The tree really does not care.
Mulching young trees is more important to overall establishment and growth than fertilization or other practices. The removal of the sod and creating this zone of root development will help develop a healthy tree. Don’t follow the bad examples done by many grounds maintenance firms and unknowing neighbors. Join my soap box and spread the word about the importance of correct tree mulching for success.
Have questions?
The Garden Hotline is staffed by trained EMG volunteers and Extension staff who will assist you with questions.
Phone: (913) 715-7050
Email: garden.help@jocogov.org