sheet mulch contents

Planning a serious sheet mulch project to kill a lot of grass- is there anything to NOT include in sheet mulch specifically? I know I have access to rough wood chips, a county specific “compost” made out of waste, horse manure, chicken manure, and I’m looking into coffee grounds, spent grain from breweries, and crowd sourced grass clippings/dead leaves.

Sheet mulch is normally used as a straightforward green/brown setup. The grass is "green manure." The cardboard is brown (carbon). This is where it gets weird. On top of the cardboard, you want another brown. Sticks, twigs, aged wood chips, etc. Then alternate greens and browns. You can stop at putting grass clippings and other greens on top of the woody material, then cover it with compost or soil if you want to plant into it right away. As long as there is no toxic gick in any of your components, you should be fine. Just alternate green, brown, green, brown until you get the depth you want, then cover it with a final layer of compost. Or don't if you don't need to plant in it yet. Just stack them up and let them mellow. And don't forget to soak the grass and then the cardboard when you start. I mean, that cardboard really needs to be saturated. Wetting the grass first helps in that endeavor.

Jim

Only thing I'd watch out for is the horse manure if it's not well composted, it can be full of weed seeds that survive the gut and you end up with a carpet of grass coming through. The county compost can be hit or miss too depending on what they screen out. I'd do a small test patch with it before committing the whole lot. Everything else on your list sounds fine, coffee grounds and spent grain are both great nitrogen sources.

Horse manure can have something even nastier and you won't know until it's too late: persistent broadleaf herbicides. Some farmers use this toxic gick on hay paddocks to kill things like dock and thistle but not grass. The hay ends up full of the stuff, and then it goes through the horses (can't be good for them either), and you can probably guess the rest of the story. I saw a friend's garden last summer after she used some free local horse poop on her beds. The plants were pretty much a total loss...it looked awful.

Here are Paul's concerns:

https://permies.com/t/2157/concerns-cardboard-newspaper-mulch

https://permies.com/t/33167/composting/Pauls-opinion-cardboard-compost

If you have time on your side and the goal is to turn a grassy area into usable space, I have found that a THICK (12"+) layer of coarse arborist wood chip does the job well.

Originally I would place a smothering layer underneath this made of a layer of kraft paper but I have had decent success. If somehow any weeds do persist, they tend to come up (root and all) with ease via hand weeding.

Over the past two years, when I've gotten chips delivered to my property, I initially used some and let the rest sit. For nearly a year each time.

You can say it was because I was being strategic. Or lazy. Or forgetful (oh yeah, I just remembered I had chips delivered!). My neighbors probably weren't forgetful.

Maybe it is a combination of all three. What I learned is that there were zones in the chips. For whatever reason, some sections stayed really dry and maintained air flow. So they didn't go anaerobic. Other sections basically turned into rich, moist, sweet smelling complst right there in the pile. The chips that were touching the ground decayed nicely. They were becoming one with the soil. In still other areas, the chips simply dried out and didn't do much of anything else.

This year they all went into the orchard. Next year, if I get another chip drop, I plan on parceling them out to the places they're most needed. Compost for the annual beds or for making compost tea. Soil for the raised beds. The rest for the orchard and for paths.

And just a shout-out for the thread bringing us back to Paul's concerns: You do NOT have to use paper when sheet mulching. As Tim said, a foot thick layer of chips will suppress weeds and not inhibit air/water/nutrient flow.

Jim

Timothy Norton wrote:If you have time on your side and the goal is to turn a grassy area into usable space, I have found that a THICK (12"+) layer of coarse arborist wood chip does the job well.

Originally I would place a smothering layer underneath this made of a layer of kraft paper but I have had decent success. If somehow any weeds do persist, they tend to come up (root and all) with ease via hand weeding.

When I put on multiple layers of mulch, I generally put the biggest pieces and the least rotted stuff on top (e.g. wood chips or straw). And the most rotted stuff or smallest pieces on the bottom (e.g compost or fall leaves.

Another option that I have used is to rent a sod cutter. This scalps off the top few inches of soil and sod into strips that can be rolled up or cut up and composted... but this leaves behind bare soil that can then be covered with mulch. Maybe broadfork it, throw down some old chicken feed, any soil amendments that you might want, then cover with fall leaves and top with 10+ inches of woodchips... you would have some good soil pretty quick. Especially if you could let it sit for 6 months.

**Edit - To be clear, I rented a gas powered sod cutter from home depot. I understand there are manual sod cutters that may work, but I felt it was worth it to get the spot cleared in a couple hours vs days of work. Something like this one - https://www.homedepot.com/p/rental/Classen-Sod-Cutter-SC-18HD/316822173