How to Use Cardboard as Mulch (Sheet Mulching)

By Mulch Planner Editorial Team · Published October 19, 2026 · Updated October 19, 2026

Short answer: Yes, you can use cardboard as mulch: lay plain brown corrugated cardboard (tape and staples removed) over mowed grass, overlap the edges by at least 8 inches, soak it, and cover it with 2–3 inches of compost or wood mulch. It smothers lawn and annual weeds and breaks down into the soil over several months.

Laying cardboard under mulch is the easiest way to turn lawn or weeds into a new bed without digging. Done well — plain cardboard, generous overlaps, soaked and covered — it smothers grass while the layers above turn into soil. This walkthrough follows Oregon State University Extension's sheet-mulching guide.

Step by step

1. Prepare the site. Mow or scalp the grass as low as possible and loosen the soil with a fork. Dig out persistent perennial weeds first — sheet mulching may not smother them.
2. Pick the right cardboard. OSU: use "plain-brown corrugated" cardboard, "not shiny, glossy, or printed", and "remove any tape or staples before laying the cardboard down."
3. Overlap generously. Lay 4–6 overlapping layers of cardboard, newspaper or heavy paper, overlapping edges "by at least 8 inches" so grass can't find a gap.
4. Soak it. "The cardboard should be well-soaked with water before application."
5. Build layers (optional, for a lasagna bed). Alternate green (nitrogen) and brown (carbon) materials 1–6 inches each, watering lightly as you go, and finish with a brown layer.
6. Cover with mulch. Top with shredded bark, wood chips or another compostable mulch so the cardboard stays wet and out of sight.

When can you plant?

Fall is an excellent time to start: OSU says the new bed "should be ready for planting in approximately six months", when the original materials are no longer recognizable. To plant sooner, add a 2–3 inch layer of compost or garden soil on top and plant into that.

How much mulch to cover the cardboard?

For a simple sheet-mulched bed (cardboard + mulch, no lasagna layers), Iowa State Extension suggests 1–2 layers of cardboard covered with wood mulch or compost. At 3 inches of wood mulch:

Formula: sq ft × 3 ÷ 324 = cubic yards; bags rounded up. For other depths use the mulch calculator.

Cautions

• Thick cardboard can restrict water and air to existing tree and shrub roots — keep it out of established root zones or use thinner layers.
• If you will water with drip lines, lay them before the cardboard.
• Results vary by climate; your local extension office can confirm the method for your region.

Worked example: how much cardboard and mulch for a 10 × 20 ft bed

Overlaps eat up cardboard faster than most people expect. Here is the math for a 200 sq ft bed (10 × 20 ft) using 3 × 3 ft flattened boxes.

1. Effective coverage per sheet. With an 8-inch overlap on each side you join, a 36-inch sheet adds only 36 − 8 = 28 inches of new ground in each direction: 28 × 28 = 784 sq in, or 784 ÷ 144 = about 5.4 sq ft per sheet instead of 9.
2. Sheets per layer. 200 ÷ 5.44 = 36.7, so round up to 37 sheets for one layer. Iowa State suggests one or two layers of cardboard under mulch, so a double layer needs about 74 sheets. Bigger sheets mean fewer seams, which is why OSU recommends large pieces.
3. Mulch on top. 200 sq ft × 3 in ÷ 12 = 50 cu ft. 50 ÷ 27 = 1.85 cubic yards, or 25 bags of 2 cu ft.
4. Optional planting layer. To plant right away, add 2–3 inches of compost first. At 2 in: 200 × 2 ÷ 12 = 33.3 cu ft = 1.23 cubic yards.

For a single 4 × 8 ft raised bed (32 sq ft), 3 inches of compost or mulch is 32 × 3 ÷ 12 = 8 cu ft, or 4 bags of 2 cu ft. Run your own bed dimensions through the mulch calculator.

Common sheet-mulching mistakes (and how to fix them)

If weeds do push through the cardboard edges later, treat them the way you would in any bed: pull them young and top up the mulch — see using mulch to prevent weeds.

Frequently asked questions

Is it safe to use cardboard as mulch?

Plain brown corrugated cardboard is the recommended type. Oregon State University Extension advises avoiding shiny, glossy or printed cardboard, which is harder to compost, and removing all tape and staples first.

How long does cardboard take to break down under mulch?

OSU Extension says the cardboard layer breaks down after several months, depending on soil type and region, and a lasagna bed may take 6 months or longer before it is ready for planting.

Can you put cardboard directly on grass?

Yes. Mow or scalp the grass as low as possible, lay the cardboard with edges overlapping at least 8 inches, soak it, and cover it with compost or mulch so it stays wet.

Can you plant through cardboard mulch?

Yes. OSU notes you can cut holes in the cardboard to set new plants; if you plan to use drip irrigation, install it before laying the cardboard.

Will cardboard kill bindweed?

Not reliably. OSU warns sheet mulching may not smother blackberry, bindweed, morning glory or quackgrass, so dig these perennials out before you lay the cardboard.

Sources

• Oregon State University Extension, EM 9559 "Sheet mulching and lasagna composting with cardboard" (revised July 2025)
• Iowa State University Extension, "Using Mulch in the Garden" (reviewed February 2026)
• Iowa State University Extension, "What mulches work well for weed suppression in the vegetable garden?"

Related guides

• Using Grass Clippings as MulchMulching basics

  Can you use grass clippings as mulch? Yes: apply thin layers up to 1/4 inch, let each dry, and never use clippings from lawns treated with herbicide in the past month.

• Types of Mulch ComparedBuying guides

  Different types of mulch compared: shredded bark, wood chips, pine needles, straw, grass clippings, leaves, compost, rock and rubber, with depth and pros and cons.

• When Should You Mulch?Mulching basics

  Spring or fall? When to mulch beds, when to add winter mulch (when the ground is about to freeze) and a simple mulching calendar, with extension sources.