We are often asked by clients and sometimes by neighbors who are watching us do an installation, “Don’t you use fabric or plastic under the mulch?” The answer is that generally we don’t use fabric when we are installing wood mulches. There is a feeling that covering the soil with fabric will help to stop weeds. But almost all weeds originate from seeds that float down from the air and start from the top of the mulch surface not from the existing soil. The goal is to make sure the few weeds that can start from the soil - like thistles, vetch, merrybells - are sufficiently eradicated prior to installing the new bed. The other reasons we don’t use fabric under hardwood mulch is that (1) it tends to make the mulch slide off the surface (2) there is nothing worse than having a nice garden bed with an edge of fabric sticking up and (3) it makes weeding and plant transplanting extremely annoying once the roots grow into the fabric.

Now, we do use fabric under rock mulch, but for a different reason. Although rock mulch has fallen out of favor, it can be an effective mulch for a shrub bed or other bed that you don’t plan on ever digging in. Fabric is used in a rock mulch bed because you want to make sure that no soil gets into the rock mulch, so you are separating the rock mulch from the soil below. Rock mulch, like all garden applications, is not a NO-MAINTENANCE solution. In order to be effective the home owner should regular blow out leaf, tree seed and other organic debris out of the bed. Overtime this debris will break down creating little soil deposits - the perfect medium for weed germination. This is a regular occurence at the edge of rock mulch beds next to sidewalks.

SUBQUESTIONS:
“What if my beds have been completely taken over by pernicious perennial weeds?” We occassionally talk to home owners who want to do a garden makeover and have beds that have been completely invaded by merrybells, thistles, lily-of-the-valley, weed trees, snow-on-the-mountain, creeping charlie, and other weeds that are perennial. As opposed to the discussion above these weeds often colonize by spreading through the soil rather than growing from seeds on top of the soil. They survive the winter and start up again in the spring. Eradicating these weeds can be challenging and should be taken very seriously - we’ve learned this the hard way. A one time hand weeding will not get rid of these invaders.

Repeated applications of Round-up will often knock these weeds back to a point that the remaining survivors are easier to contend with. But a technique we favor is called “sheet mulching.” This technique includes covering the bed with corrugated cardboard or thick layers of newspaper and topping this with 6-8″ of mulch. This should stay in place for at least a year. The following year you can remove some of the excess mulch and plant.