by Charlene Burgi
"Save the cardboard!" is the mantra around our house every time a package arrives in a sturdy box. What becomes of all those boxes? They go into the garden as sheet mulch—a simple solution for suppressing weeds, building healthy soil, saving water, and even replacing unwanted lawns.
By saving cardboard, one becomes an aficionado of the paper product. For example, our golden retriever Sassy must eat a special dog food that is sent via USPS. The boxes containing her food are extremely heavy weight compared to the boxes that hold her sister Misty's canned dog food purchased at the grocery store. Both boxes work well for sheet mulching, but I save the heavy-duty boxes for areas that get more traffic or have a more prolific weed population. The thicker the material, the more time it will take to break down and the longer it will hold moisture.
Saving cardboard for sheet mulching is a frugal way to do the job. Another option is to purchase rolls of cardboard available at your local irrigation supply house and at some garden centers. This rolled product saves the time spent removing staples and tape from boxes, and it is much neater to install. On the other hand, I view the box method as a great way to repurpose refuse. Either method will add nutrients to the soil as the cardboard decomposes.
So why sheet mulch? And when is a good time to start? Sheet mulching is an easy way to keep weeds at bay for an extended period of time. Laying cardboard over a wetted area of weeds and covering with mulch will save you the dastardly job of pulling weeds. Even with a layer of mulch applied 3 inches thick, weeds can come up through the mulch. But by adding cardboard first you thwart light from gaining access to the soil, preventing weed seeds from germinating. The trick is to overlap the cardboard to prevent light from going into the gaps. Once the cardboard is down, top with mulch and your garden can be weed-free. Over several years, the cardboard will break down and need to be replaced about the time the mulch requires a fresh layer. The bonus is the new cardboard and mulch can go right over the top of the old.
| Sheet mulching over an unwanted lawn
The best time to sheet mulch is right now. Fall is often a time when new landscaping is installed. If you are replacing a lawn, sheet mulch over the top of your lawn. Sheet mulch in a newly designed planter or area prior to installing plants. Sheet mulch before refreshing the mulch in planters. Sheet mulch natural pathways to abate weed growth. Winter is coming and weeds will start to grow—especially if we get the rains that are predicted with El Niño. Couple a few good rains and some balmy days we know to expect in February, and you have the perfect recipe for optimal weed germination and growth during a time we tend to avoid working in the garden. By sheet mulching now, you can avoid weeding then. Check out Marin Municipal Water District's updated sheet mulch page
for step-by-step instructions if this concept is foreign to you.
Another reason to sheet mulch right now is MMWD and Marin Master Gardeners are hosting two free workshops on "Alternatives to Our Thirsty Lawns" October 17 in Mill Valley
and October 22 in Ross
. The workshops will provide valuable information on replacing lawns, modifying irrigation systems, and designing creative landscapes in lieu of lawn. Space is limited, so pre-register for the date of your choice today. Additionally, California is offering rebates up to $2 per square foot
for replacing water-guzzling lawns with water-wise gardens. Add to that a rebate up to $50 from MMWD for organic mulch
to help with your sheet mulch project. Fall is the perfect time for planting. Take advantage of these workshops and rebates!