Homeowners who want nice landscaping, but dread maintenance tasks like weeding and mulching, often turn to pebble mulch as a solution. Pebble mulching is the practice of covering landscape beds with weed barrier fabric and then spreading a few inches of pebbles or decorative stone. Stone mulch has been widely used in commercial landscapes for many years, simply because, at least in the beginning, it discourages weeds. Wood mulches need to be renewed every year, but stone mulches can last five years or more before they need to be refreshed.
Whether used under stone mulch or wood mulch, weed barrier fabrics are an installation shortcut when making new beds. They allow landscapers to plant almost anywhere without doing anything to kill existing weeds or weed seeds. Fabrics block sunlight while allowing water to soak in, making it difficult for weeds to get a toehold. New weeds must grow in the mulch above the fabric, and since stone mulch contains no nourishment, weeds have a difficult time growing.
Stone mulch works especially well in clean environments like around in-ground pool decks, traffic islands and narrow beds between buildings and pavement. This is because grass clippings and other organic matter won’t be as likely to soil the stone mulch in such places. Also, stone mulch is less likely than wood mulch to wash onto pavements or blow into swimming pools.
There is a major downside to stone mulch. Plants breathe through their roots, so loose, fluffy soil is far healthier for plants than compacted, hard-packed soil. Even if landscape beds are deep-tilled with compost or peat moss before planting, adding tons of stone on top quickly squeezes out all the air and packs the soil down hard. Most plants hate this and fail to thrive.
Weed barrier fabrics choke most perennials, preventing them from “colonizing”. Perennials that spread underground, like ornamental grasses, daylilies and daisies, are confined in a hole in the fabric and eventually run out of energy. Winter hardiness is affected as well. Unlike wood mulches, which insulate plant roots, stone mulches conduct and hold freezing temperatures, so soil temperatures stay much lower under stone mulch.
If stone mulch is used adjacent to lawn, some sort of edging must be used to contain it and keep the lawn grasses from creeping in. Eventually all stone mulches fill up with organic matter. Leaves, clippings, windblown weed seeds, fruit from plants and perennials, bird droppings and other debris between the stones provide an ideal environment for weeds to get established. Weeds in stone mulch are harder to pull, so they must be sprayed. It’s only a matter of time before stone mulch beds need to be cleaned out and the old, dirty pebbles replaced with new.
If you’ve ever had to clean out old pebble mulch (and we have, plenty of times!), you can appreciate how hard it is to remove tons of pebbles and peel up the old weed barrier before you can till and plant. Unlike wood mulches, which improve soil when they’re tilled in, stone mulches must be painstakingly removed in order to refresh your landscaping. This is backbreaking work. Now you discover that plant roots have been spreading far and wide just under the weed barrier, licking the condensation from under the fabric instead of finding subsoil moisture.
There are trade-offs in every aspect of landscaping. If you want to save maintenance in the short term by using stone mulch, just do it with your eyes open. Perhaps do some areas and not others. In any case, the success of your landscaping depends on thorough soil preparation before you plant. Pebble mulch or wood mulch, fabric or no fabric, the whole point of gardening is to have healthy plants.
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.