What to Know About Mulch - as part of the expert series by GeoBeats. Mulch is a great way to keep a neat look, to keep moisture in the ground, and also to maintain the weed control. We always tell people to use at least 2-3 inches of mulch when they apply mulch. Another thing to consider is what type of mulch. Some mulches have a high acidity level, and do not work well with some plants. So it is important to know what mulch you are using before you use it. One of the big common mistakes that people make with mulching is they tend to mulch around the base of the plant. That really is a problem, because it creates too much moisture around the bark of the tree, for instance, and it ends up actually decaying the tree. So it is really important not to keep mulch at the base of a tree or a bush or a plant, you don’t want to smother it. You just want to lay it out, you want to make it nice and airy, and it will do what it is supposed to do.