Last Updated on October 9, 2026

Sheet Mulching Calculator: Cardboard and Compost for a No-Dig Bed

Sheet mulching is cardboard laid over mowed grass, soaked, then covered with alternating layers of greens and browns at least 18 inches deep, with a brown layer on top. That is the method in Oregon State University Extension’s guide Sheet mulching and lasagna composting with cardboard: 4 to 6 overlapping layers of cardboard or heavy paper with edges overlapped at least 8 inches, then alternating greens and browns layers of 1 to 6 inches each, and a bed ready to plant in about six months. Enter your bed size below to get the cardboard, the cubic feet and bags of each layer, and cubic yards if you are ordering bulk.

Sheet mulching calculator

Enter the bed in feet and the layers in inches. The defaults are a 4 by 8 foot bed, 4 layers of cardboard from 3 by 4 foot flattened boxes, 2 inch greens and browns stacked to 18 inches, and a 3 inch compost cap. Set the cap to 0 if you will wait for the bed to break down.

The results table already shows the default 4 by 8 foot bed, so you can read it even before you change anything.

The layers, bottom to top

All five rows come from the Oregon State guide. Greens go on first because the cardboard itself is carbon, and browns finish the stack as a cover to ward off insects. NC State Extension’s sheet mulching article uses 2 inches per layer and starts with browns instead. The calculator follows Oregon State’s order.

The cardboard step itself also differs by source. NC State and University of Vermont Extension each describe a single layer of cardboard or newspaper, overlapped at the seams; Oregon State’s range of 4 to 6 overlapping layers is thicker. The calculator defaults to Oregon State’s low end of 4, and you can set it down to 1 if you would rather follow the single-layer approach.

Worked example: a 4 by 8 foot bed

A 4 by 8 foot bed is 32 square feet. Every inch of depth over 32 square feet is 32 ÷ 12 = 2.67 cubic feet.

• Cardboard. Turn a 36 by 48 inch box so the 48 inch side spans the 4 foot width. Along the 8 foot (96 inch) length, the first box covers 36 inches and each one after it adds 28 (36 minus the 8 inch overlap): 36 + 28 + 28 + 28 = 120 inches, so 4 boxes per layer. Four layers is 16 boxes, 192 square feet of cardboard for a 32 square foot bed.
• Greens and browns. One green plus one brown layer is 4 inches. 18 ÷ 4 = 4.5, rounded up to 5 pairs so the stack reaches at least 18 inches and ends on a brown. That is 10 inches of greens and 10 inches of browns: 32 × 10 ÷ 12 = 26.67 cubic feet each.
• Buckets and bags. A gallon is 0.134 cubic foot (7.48 gallons per cubic foot), so a 5-gallon bucket holds 0.67 cubic foot and a 30-gallon lawn bag about 4. 26.67 cubic feet is 40 buckets or 7 lawn bags of each.
• Compost cap. 32 × 3 ÷ 12 = 8 cubic feet, eight 1 cubic foot bags. All layers together are 61.33 cubic feet, or 61.33 ÷ 27 = 2.27 cubic yards loose.

That is a lot of leaves and clippings for one bed. University of Missouri Extension’s lasagna gardening article says to stockpile ingredients through the year. You can also build the bed a little at a time as materials turn up.

How to sheet mulch over grass, step by step

These steps follow the Oregon State guide.

1. Cut the grass short. Mow or scalp it as low as the mower goes, over the full length and width of the bed. A 3 foot width lets you reach the middle from either side.
2. Loosen the soil underneath. “Pop” the soil with a spading fork or broadfork for drainage.
3. Pull the tough weeds. Dig out blackberry, bindweed, morning glory and quackgrass first. The layers may not smother them.
4. Lay the cardboard with no gaps. Overlap every edge at least 8 inches; weeds come up through any opening. Big sheets mean fewer seams.
5. Soak it. Wet the cardboard thoroughly before anything goes on top, so water gets through and it starts to break down.
6. Greens, then browns. Spread the first green layer, then a brown layer of the same depth. Water each layer lightly as you go. Sprinkle a few handfuls of soil between layers to bring in the microbes.
7. Stack and finish brown. Keep alternating to 18 inches or more, ending on browns.
8. Wait, or cap and plant. Leave it to break down, or add 2 to 3 inches of compost or soil and plant now.

Fall is an excellent time to build, since the layers break down slowly over winter and are ready in spring. As the stack settles you can keep adding layers, always ending on browns.

What cardboard to use

Use plain brown corrugated cardboard, not the shiny, glossy or printed kind, which is harder to compost. Pull off all tape and staples first. Do not stack it too thick either, because that slows its breakdown. With several layers, poke holes in the upper ones so air and water move through without opening a path for weeds. All of that is from the Oregon State guide, which also points to local businesses as a ready source of boxes.

University of Vermont Extension’s lawn-to-garden guide gives a paper option: 10 sheets of regular, not glossy, newspaper in place of cardboard, overlapped 8 to 10 inches. With a 4 to 6 layer range on one side and the too-thick warning on the other, the calculator lets you pick 1 to 6 layers.

When can you plant?

Oregon State calls a bed finished when you can no longer recognize the original materials and it looks and smells like fresh earth. It is a slow process with little or no heat from the microbes, and a bigger stack takes longer than a small one. To plant without a cap, build it at least 26 weeks before you plan to plant. Spring planting dates key off your last frost, so look up your date on the Plan My Garden frost dates page and count back from there.

Expect it to shrink. Missouri Extension describes a bed that starts as 24 inches of layers and cooks down to 6.

Planting into a sheet mulched bed

• Through the cardboard. You can cut holes in it to set plants in, but it is hard to tell if the soil below is getting enough water, so run drip line before the cardboard goes on if you plan to plant through it.
• Into the mulch. Scrape the mulch aside where each plant goes and make sure you are planting into soil, not mulch.
• Seeds and root crops. Plant seeds no more than a quarter inch deep with a light covering of soil; root vegetables grow well in a lasagna bed and pull easily at harvest.

Steps from Oregon State, University of Vermont and Missouri Extension.

Greens and browns: how much of each

Oregon State’s method uses equal layers of greens and browns, though its footnote notes that most compost recipes call for about twice as many browns as greens by volume to reach a 30 to 1 carbon to nitrogen ratio. Missouri Extension’s rule of thumb is the same: two parts carbon to one part nitrogen, in alternating layers. To build it that way, set the browns layer to twice the greens layer in the calculator. To check the mix of the exact materials you have, use the compost ratio calculator.

For browns, shredded leaves are free in October and they are my first choice. Shred them first: on a small bed, whole leaves mat into a wet sheet. How to Make Leaf Mold covers shredding and wetting them. For greens, Missouri Extension gives two cautions: manure from pasture-fed cattle can carry residues that damage plants, and manure or hay with seed heads brings more weeds.

Sheet mulching pros and cons

Unless marked, the pros and cons come from Oregon State’s guide, which also suggests checking with your local extension office on whether the method suits your region.

Already have beds? Skip the cardboard

Sheet mulching is for ground that is still grass.

• Already have a bed? Skip the cardboard. My fall routine is simpler: I lay two inches of compost on top of every emptied bed and walk away, then plant straight into it in spring. See Empty Raised Beds in Fall: Two Inches of Compost and Walk Away.
• Building inside a new raised bed frame? Oregon State’s easy method is cardboard on the grass, layers of leaves, coffee grounds, grass clippings and straw, then 4 to 6 inches of garden soil on top. The raised bed soil calculator gives the soil volume.
• Starting from bare ground with no plan yet? How To Start A Garden From Scratch walks through the rest.

Quick questions

How long after sheet mulching can you plant?

About six months for a full stack of greens and browns. To plant sooner, sift 2 to 3 inches of compost or garden soil on top and plant directly into it.

Can you sheet mulch over grass?

Yes. Mow the grass as low as it goes, loosen the soil with a fork, lay plain cardboard with edges overlapped at least 8 inches, and soak it before adding layers. Dig out bindweed, quackgrass and blackberry first, since the layers may not smother them.

What kind of cardboard is best for sheet mulching?

Plain brown corrugated cardboard with all tape and staples removed. Skip shiny, glossy or printed cardboard, which is harder to compost, and do not make the layer too thick.

How many layers of cardboard do you need?

Oregon State University Extension calls for 4 to 6 overlapping layers of cardboard, newspaper or heavy paper, with edges overlapped at least 8 inches. It also warns that a layer that is too thick slows decomposition, so the calculator lets you pick 1 to 6.

Does sheet mulching actually work?

Yes, for smothering grass and weeds and building soil without digging, but it is slow, about six months for an uncapped bed, and tough weeds like bindweed or quackgrass can come through.

Let the planner place them

Build the bed this fall, then draw it in the planner. Plan My Garden is free to start: enter your zip code and it finds your frost dates, draw your beds, pick your spring crops, and it places each plant at square-foot spacing and builds a planting schedule from those dates.

Related: Compost Ratio Calculator · Raised Bed Soil Calculator · How to Make Leaf Mold · Empty Raised Beds in Fall · Composting for Beginners · How To Start A Garden From Scratch · Charts and Tools