Wednesday, June 10, 2009

Weeding in sheets is 'mulch' easier

by Melanie Lopes, Restoration Specialist

“Is there any easier way to do this?”
“Can’t you just get a bulldozer and clear this whole area?”
“Isn’t there some sort of spray that you can use on these plants to get rid of them?”

These are questions that we often hear from volunteers participating in weeding projects through our Community-based Restoration program. The work, albeit satisfying, is labor intensive and time-consuming, and after about an hour’s worth of pulling, digging, and lopping, people start to wonder if there’s a better way.

The manual removal that we do with volunteers is an effective strategy for thoroughly removing populations of weeds in areas where native plants are present. Bulldozers, power tools, and herbicides, however time-saving they may be, are not as selective, and simply are not options given the nature of our sites and the nature of a community-based program.

However, we have found a technique for weed management that is efficient, effective, and appropriate for our programs – it's called sheet mulching. And it's a technique that can be used to eliminate large areas of weeds while simultaneously enriching the soil. It involves smothering the weeded area by laying down a layer of compost, then cardboard, followed by a thick layer of mulch (wood chips, straw, leaf litter, etc). As time passes, the cardboard and the existing weeds underneath begin to decompose, adding nutrients to the soil. Furthermore, sunlight is blocked from the soil, preventing future weed germination. This creates a blank slate for planting native seedlings in enriched soil, without competition from aggressive weeds.

Here are a few photos to show you what we mean.

So far, we have tried this technique at only one site, along a trail at the Palo Alto Baylands. We chose an area that was covered solely by non-native plants, making it easy to completely cover the area without fear of destroying any natives. With the generous contributions from the City of Palo Alto, we had enough compost, cardboard, and mulch delivered to the site to get the project underway. In the fall of 2006, a group of volunteers from PG&E came out to help install the first section of sheet mulch – an effort that was met with great success. The area was left to rest for one year, in order to allow the cardboard and weeds to decompose. The following winter our first plantings went in and the results were phenomenal. Three years later, the area is thriving with native plants, with hardly any weeds in sight!

We've expanded the sheet mulch area down the trailside, and we hope to continue using this technique at other sites as well. Finding appropriate areas for this approach and acquiring the necessary resources (cardboard, compost, mulch) are the main obstacles we face, but based on the remarkable results we’ve seen down at the Palo Alto Baylands, we know that getting another sheet mulch project underway is well worth the effort.

Sign up for one of our Community-based Restoration programs at

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