Sometimes I advise clients to use mulch in their gardens, and sometimes I advise them not to, but most often I advise them to use it wisely. Why? Because many times mulch is used for the wrong reasons and incorrectly, causing more harm than good…
Mulch is beneficial for keeping moisture in and keeping weed levels down, but it must be applied properly. Applied incorrectly, too thick or too close to plants, it can cause rot, mildew/mold and eventually the demise of your perennials, shrubs and even large trees.
Mulch should not be piled right up to the base or stalk/stem of your plants. When applying mulch to your gardens you should leave a space of at least 1 inch (so the soil shows) between the base or stalk/stem/trunk of your plant or tree and the mulch. After a heavy rain and in the spring after snow has moved the mulch, you should reestablish this space as soon as possible, especially for young plants that will rot quickly if the mulch is left too close to the stems.
Mulch applied too thickly around the base of a tree will eventually kill the tree. The roots of all plants, including large trees, require oxygen, moisture and nutrients. If mulch is applied too thickly, these required items cannot reach the roots, causing starvation and death of the plant. This theory also applies to ornamental rocks and anything else piled around trees to minimize the growth of weeds and grass. These pictures show mulch piled much too thickly around the base of a mature tree(incorrect), and removed from the base and spread out (correct):
Mulch will keep weed levels down, but it will not eliminate weeds altogether as many people are led to believe. Weed seeds blow in the wind and will settle in the mulch and germinate there too. The difference is, when you pull out a weed growing in mulch, it comes out much easier and more completely, with the root intact. If you do not remove the entire root of a weed it simply grows back, often very quickly.
Mulch applied in a thin layer (one inch thick is plenty) around a tree can be beneficial to keep weeds and grass roots from competing with the tree roots for oxygen, moisture and nutrients. Just remember, more is definitely NOT better!
Nothing, including grass, should be planted around a new tree for the first five years, allowing the tree roots to get established. After that, shallow rooted perennials or annuals work best as they do not force the tree roots to compete for required elements. A few examples of shallow rooted perennials are geraniums, sweet woodruffe and lamium. My personal favourite is the perennial geranium (very different than the red annual geraniums that I am not so fond of) because it tolerates almost full shade to almost full sun, and is the first plant to green up in the spring. Perennial geranium flowers can be white, pink, blue, purple and many shades in between, but are almost inconspicuous in many of the varieties; the foliage is the main attraction to me:
If you do decide to mulch your garden or use mulch under your trees, please use caution and apply it correctly so you do not do more damage than good…