Q: I have a question about pine straw mulch. I’ve used it for years and will be putting out new pine straw in a few days. For years I’ve read and heard that the old pine straw should be cleaned out before the new stuff is put down, but I’ve never questioned why. It seems that the deeper the mulch the better it would perform. What is the reason for this particular advice?
A: There are two reasons: because deep mulch attracts insects and because weed seeds will sprout in the decomposed straw layer below the fresh layer.
Dr. Dan Suiter, Director of the Urban Pest Management Center in Griffin, says that you walk a thin line when using mulch under shrubs near your home. On one hand, you want to conserve water for the plants by applying mulch. On the other hand, moist spots under the mulch make an excellent hiding place for insects such as roaches, ants and scorpions, who might wander inside your home. His recommendation is to keep mulch twelve to sixteen inches away from the foundation of your house and to replace it every year.
You’ll also find that if you leave mulch in place for several years the layer close to the ground decomposes into a layer of rich soil – a perfect place for weeds to sprout. In addition, if the layer is moist constantly, a thick mat of white fungus will grow in it. If it dries, the fungal layer becomes water repellent, so any subsequent irrigation is prevented from going to the roots of your plants. Keep these points in mind when you decide whether to add more mulch or to replace it with fresh material.