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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Apr 21


Posted on April 21, 2017 at 9:17 AM by Ann Vallee

by Charlene Burgi

sheet mulching benefits
Top to bottom: 1) Weedy area in need of sheet mulching. 2) Mulched bed ready for spring flowers. 3) Last summer’s vegetable garden—sheet mulched and weed-free
For years I have championed the benefits of mulching and specifically sheet mulching. This year is no different, except for the knowledge of what will occur due to the vast quantity of rain we've experienced this past winter. 

Let's face it: This year weeds are going to be a particular challenge. The wet weather coupled with the occasional warm, sunny days are just enough to cause weed seeds to germinate at an alarming rate. Follow those sunny days with healthy doses of storms acting as irrigation, and we are all looking at bumper crops of weeds. As much as I hate to say it, it’s the perfect storm for weeds. 

There are numerous ways to deal with this unwanted vegetation, but sheet mulching is weed suppression at its best. It is environmentally friendly, builds healthy soil, and is simple and inexpensive. See our step-by-step guide

With sheet mulching, there’s no need to clear weeds first. You can sheet mulch right over the top of them—or even over the top of an unwanted lawn. Overlapping rolls of cardboard or flattened boxes prevent weed seeds from germinating. By eliminating light, the cardboard also kills existing plants by depriving them of the energy needed for photosynthesis. Eventually, the decayed plants will add nutrients to the soil as they are cycled back into the earth. 

When sheet mulching, I always add a two- to three-inch layer of organic material such as bark or straw on the top of the cardboard. The organic material will also break down in time and aid in building healthy soil. When the cardboard and bark have broken down, simply add another layer of each on top. You will be amazed at the rich soil you can build through this process.

What attracts me even more to this method of achieving healthy soil is the ease of weeding in areas that have been sheet mulched. Any weeds that manage to find their way into these areas are easy to pull out. 

My flower beds this spring are a prime example of the labor-saving benefits of sheet mulching. One flower bed has a healthy layer of bark and few weeds. On the other hand, exposed soil in the flower bed to the south is sporting weeds about eight inches high at the moment. I never mulched that area, as the plants went into containers that sat in that space. The price for my lack of forethought will be the extra effort needed to tidy up the area this year. 

Tomorrow I’ll break down the cardboard boxes I’ve been saving to sheet mulch that area. Bark will complete the project, and the health of the garden will be restored in all of those beds with the promise that next year won't be as labor intensive. Already this year will be a lot less effort than if I tried to pull all those weeds by hand. With Earth Day coming up this weekend, sheet mulching seems like the right way to celebrate!


Anonymous User
April 21, 2017 at 12:19 PM
Charlene, thank you for your material on sheet mulching. I will give a try. Another subject if you don't mind. Do you know of a ground cover to replace about 400 sf of grass that is less water intensive and is short if mowed and resilient enough to allow walking and some other light activities every so often like kicking a ball for 15 minutes? I live in Mill Valley Thank you, Adrian
Anonymous User
April 21, 2017 at 1:20 PM
Yes, sheet mulching works. Aside from just breaking down cardboard boxes, I learned you can call a moving company to get large boxes and they have corrugated cardboard on rolls; appliance stores for huge boxes. If you ask at the grocery store, they will tell you when you can pick up their broken down boxes after reshelving/stocking.
Anonymous User
May 1, 2017 at 8:00 AM
Adrian. Sorry for the delayed response but I was on vacation. To be honest, there is nothing like a lawn for wear and tear. However, I just planted 48 Veronica liwanensis (Turkish speedwell) at my place. I planted one 4 inch size container last fall to see how it would perform during winters here and was amazed at its tolerance to weather conditions including drought conditions during the fall. I do not know how it will perform to the wet winters in Marin but you might want to try a sample area first before investing in the time and cost for full replacement. This plant is a ground hugger that does not require mowing! Plant in full sun for your area. Let me know how it works out!

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