As most gardeners know, there are many, many benefits to mulching. But that doesn’t mean there aren’t a few problems associated with mulching too. For the most part, mulching problems come from improper mulching and luckily, they are reversible and easily controllable. But forewarned is forearmed, and better to know how to do it right before you do it wrong, n’est pas?
Common Problems with Mulch
Here are the most common mulch problems and how to solve them:
Some organic mulches (like pine needles) are high in sulfur. Repeated mulching with high-sulfur mulches can lower the alkalinity of your soil, making it suitable only for acid-loving plants. To avoid changing the pH or mineral content of your garden soil, use inorganic mulch like pulverized rubber, plastic sheeting or garden fabric, use relatively inert organic mulches (like cocoa shells), or use mulches that are slow to decompose (like bark chunks).
Mulch that isn’t handled properly can “sour,” producing toxic substances like acetic acid, hydrogen sulfide gas, methanol and ammonia. Bad mulch has an extremely low pH value (roughly between 2.0 and 2.5) and often smells like vinegar, ammonia or sulfur. To keep your mulch from going bad, turn it occasionally (once or twice a month is appropriate, or even more if your mulch is very wet) and don’t let your mulch layer get too thick. Should your mulch sour, turn it repeatedly over the course of a few days. The aeration should eliminate any toxic compounds within two to three days.
Heavy mulch left on too long can cause perennials to emerge too early and for growth to be weak and fragile. Tender early growth like this is prone to permanent injury and kill off from temperature drops and late freezes. To avoid these problems, use mulch only as directed. It’s always tempting to try and outsmart directions by using a little more than directed (at least that always works with vanilla and chocolate chips!), but don’t spread your mulch too thickly, and just resist the urge to “double up.” More may seem like better, but when it comes to mulch, that’s rarely the case.
If you crowd mulch against the bases of your plants, you may encourage slugs and bugs to set up house and start snacking on your plants (especially if you’re mulching your vegetable garden). To deter slugs and most garden bugs, keep mulch at least a few inches from plants. If that doesn’t work, try burying a circle of copper wire around plants to ward off cutworms; for slugs, try putting out slices of citrus fruits. The slugs will gather and snack around the fruit slices, making it easier for you to capture and dispose of them.
Because organic mulches decompose and add nutrients to the soil, they can significantly alter soil composition. For instance, mulches high in carbon (like straw and sawdust) can encourage nitrogen depletion in soil, and mulches high in sulfur (like pine needles) can increase the acidity of your soil, making it intolerable to plants that like neutral or alkaline environments. To avoid these problems, understand the different types of organic mulches and how they’ll impact your soil before you use them, and if you’re using a nutrient-rich or nutrient-depleting mulch, be sure to test your garden soil yearly to monitor changes in your soil.
Mulches retain moisture, so slime molds, various fungi and moisture-associated diseases like powdery mildew can all become issues. To minimize fungal problems, keep soil from becoming too wet; control mushrooms, molds and fungi by hand-picking; and try any of these natural cures for powdery mildew.
The Benefits of Mulching Outweigh the Problems
Seeing a long list of mulch problems may make you wonder if it’s worth the effort. Well, as any regular gardener will tell you, it absolutely is. Used properly, mulch can make a world of difference in the amount of time spent dealing with garden chores (like weeding, watering and fertilizing). You just need to know a few basic rules and have a general idea about the differences between mulches.
For more information about mulching and mulches, see The Benefits of Mulching, or for more information about gardening in general, see my Gardening Guides page. There you’ll find plenty of gardening resources and in-depth guidelines and specifications for growing your favorite herbs and vegetables.