By Elizabeth Joseph, garden and education coordinator at Heifer Farm

If you take a peek at the to-do list for the Heifer Farm garden at any point during the growing season, you’ll find the predictable tasks of watering, seeding and harvesting. What you might not expect to find is a standing line item to pick up cardboard, but it’s there, and it’s a big part of how we grow delicious and nutritious veggies. We use cardboard in the garden to improve the fertility of the soil, prevent weeds and install new garden space when needed. Read on to learn how to transform cardboard from a product that usually ends up in the waste stream to a soil-enhancing, microbe-boosting, weed-smothering all-star in your garden toolbox.

Photo by Russell Powell

The Other Black Gold

Heifer Farm isn’t the only place you’ll find gardens teeming with worms. Heifer gives them to farmers because the worms eat organic waste and convert it into top-shelf fertilizer. The process is called vermiculture, and the worm castings (that’s the poo) produced from it are so valuable to farmers that they are sometimes called “black gold.” Worms are composting machines, and farmers can turn waste into profit by cultivating them in compost bins and selling the high-quality fertilizer.

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.

How to Use Cardboard in a Garden

Break down packing boxes and remove any tape or labels.
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.
Improve soil fertility even more by layering mulches or organic matter on top: compost, shredded leaves, grass clippings, straw, you name it! At Heifer Farm, we 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!

Heifer Farm's Rhubarb Crisp

Photo by Elizabeth Joseph

• 2 pounds rhubarb, diced
• ¼-½ cup sugar
• 3 tablespoons corn starch
• ¾ cup butter
• ½ cup brown sugar
• ½ cup flour
• 1 ½ cups oatmeal

Preheat oven to 325 degrees. Fill a 9x13 pan with the rhubarb, sugar and corn starch and toss together. In a saucepan, melt butter and sugar together. Once sugar is melted, remove pan from heat and incorporate flour. Mix oatmeal in with the sugar and flour mixture and spread over the top of the fruit. Bake for 45 minutes or until the top is golden brown and the fruit is tender.

NOTE: Rhubarb leaves are toxic! Eat only the stems. You can substitute apples for some of the rhubarb to give extra sweetness. For a vegan version, use coconut oil in place of butter.