Ask the Gardener: Why Is Mulch Used Around the Base of a Tree?

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Ask the gardener is a column in which local readers send in questions about your garden, lawn, trees and more.

Reader question: "For most of the last 35 years, I have been in Texas. We have always learned that when you plant a tree, it goes below the level of the ground a bit, and you do NOT build the earth up around the trunk. Here in Wentzville, it seems that every new tree I see has the mulch built up in a mount around the tree base.  Isn't that bad for the tree?

Expert Answer: According to TreesAreGood.com, there's a method to the mulch madness. 

For one, it can be a cosmetic improvement. Mulch at the base of the tree shows care and effort has been put into the lawn. Aside from looking nice, mulch is supposed to help control weeds. TreesAreGood says a two- to four-inch layer of mulch makes it harder for weeds to grow. Without weeds, the tree is also protected from weed whackers and other lawn-maintenance tools. 

Mulch is also good for providing soil moisture for the tree, meaning you it will need less watering to grow bigger. Mulch also is good for keeping the soil warm in the winter and cooler in the summer. 

Basically mulch is intended to act like leaves and other helpful debris found at the base of trees in the wild. 

It's important to note, however, that there can be too much of a good thing. So-called "mulch volcanoes" can kill trees instead of helping. The volcanoes can cause roots to spread up and can cause fungus problems for the trees 

Gardeners Detective July 24, 2012 at 05:58 PM
The Wentzville gardener is correct about not mounding mulch around trees and should also know the University of Missouri Extension St Charles County (a 5013c nonprofit organization) is available to answer their gardening questions specific to the area and is here to serve you. Step by step instructions for the proper way to mulch a tree http://extension.missouri.edu/extensioninfonet/printarticle.asp?id=1652 and other gardening solutions can be found on their website http://extension.missouri.edu/stcharles The various municipalities in St Charles County responsible for care of public areas are encouraged to contact the Extension Service about mulching and for sound gardening advice and proper care of public areas in our community to reassure residents their tax dollars are being used wisely. The Extension is here to serve them, businesses, and residents and are only a phone call away, open Mon. through Thurs. and can be reached at 636-970-3000. If you live in St. Charles County or have recently relocated to the area and have not visited the Extension Center lately you will be amazed by the many programs available and the onsite Master Gardeners Demonstration Garden which is handicap accessible and serves as an outdoor class room designed to show local gardeners how to grow excellence in their St. Charles County garden. The gardens are free and open to the public for self guided tours 7 days a week. The Extension is located at 260 Brown Rd, St Peters, MO 63376.
George Newell July 24, 2012 at 06:04 PM
Keep mulch off the trunk of the tree.
Fred Oompahloompah July 24, 2012 at 07:33 PM
Are grass clippings from lawn mowing recommended as mulch around trees or in Vegetable and flower gardens? This has been suggested as away of keeping down yard waste in the St. Peters area but is this advisable? Another suggestion has been to create a compost pile and add the clippings there!
Gardeners Detective July 24, 2012 at 07:55 PM
Frank, See the link on my comment above. Here is some additional information on lawn clippings and composting. http://extension.missouri.edu/p/G6958
George Newell July 25, 2012 at 08:44 PM
Fred, grass clippings not containing pesticides can be used as mulch. Just add a little nitrogen fertilizer to aid breakdown by bacterial. After decomposition the organic matter will release a small amount of nitrogen back to the soil.


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