How to prep your garden with cardboard

By Heifer International

Last Updated: May 7, 2019

How to prep your garden with cardboard

Why use cardboard in a garden? It’s a great mulch, and prevents weeds from sprouting. Decomposing cardboard adds organic matter to the soil, improving your garden’s drainage and boosting nutrient levels. Earthworms flock to the dark, moist, safe habitat cardboard provides, leaving behind a nutrient-rich layer of worm castings–free fertilizer! A layer of cardboard left in place for a season smothers out grass and weeds, creating a ready-made garden plot, no tilling required. It’s free, and you can feel great about reusing a product that would otherwise go to waste.

Photo by chuttersnap on Unsplash

Break down packing boxes and remove any tape or labels.

Save your boxes next time you move, or lay claim to a friend's boxes when they move, because packing boxes are perfect for this project. 

Mow the area where you want the garden to go.

Then, place cardboard on top, overlapping the edges a few inches so that weeds don’t spring up in the cracks.

Hose everything down with water.

The moisture keeps the cardboard in place and is important for both gas exchange and microbial life in the soil.

Compost layered with mulch hay.


Improve soil fertility even more by layering mulches or organic matter on top: compost, shredded leaves, grass clippings, straw, you name it! One method is to put down a layer of compost, followed by mulch hay on top of that.

Sit back and let the magic happen.

The decomposition time will vary based on soil biology. The more microbes and earthworms, the faster the cardboard breaks down.

Come planting time, if the cardboard is still there underneath the mulch, leave it all in place and simply cut a hole through it to access the soil surface so you can seed or transplant as usual. If you’re looking to install new garden space, start a few months or even an entire season ahead of time to kill the sod or grass you are converting to a garden. If you decide to give this a try, be ready to forever replace “it tastes like cardboard” with “it grew from cardboard and tastes great to boot!” Happy growing!

Story by Elizabeth Joseph, photos from Rutland Farm in Massachusetts.