Is Cardboard Safe For Organic Gardening?

So, you've got big stacks of cardboard put away from your online shopping. If you're thinking of repurposing them for your garden and want to find out if cardboard is safe for organic gardening, you're in the right place. We've researched the topic to provide you with the best answer.

It's safe to use unwaxed, brown cardboard with no colored prints in organic gardens. You need to remove staple wires, tape, and stickers from your cardboard.

Paper pulp is used in cardboard production. The paper contains chemicals like dioxin and BPA. Aside from that, cardboard may have more chemicals from ink and glue.

However, research shows that the amount of these chemicals on paper, ink, and glue is below safe levels and does not pose a risk when used in the garden.

Keep on reading to learn more about the components of cardboard and its safety for use in gardens. We'll also discuss what kind of cardboard to use and ways you can use them in your garden. With that said, let's dive right into this topic!

Is Cardboard Safe For Organic Gardening?

female hands hold young seedling over

Cardboard is made from paper, and these papers contain chemicals.

There is much debate on using cardboard in organic gardens. However, while chemicals may be present in cardboard, research shows that they appear not harmful.

What Is Cardboard Made From?

Let's take a look at the components of cardboard:


Paper products use the chemical dioxin in their manufacturing process. Dioxin is used to bleach paper. This includes paper food packaging, table napkins, diapers, and white coffee filters.

Anything produced from pulp that contains dioxin will have traces of the chemical. Dioxin is a known carcinogen.

But studies show that small amounts of dioxin, like the amount found in paper products, pose risks as low as zero to consumers.

Bisphenol A Or BPA

Not all paper products contain BPA. It's a color developer and can be on thermal paper, commonly used for receipts. BPA is used on many plastic products.

While you wouldn't usually use thermal paper in composting, it may have been used in making cardboard. Fortunately, the FDA states that BPA is safe for use at very low levels.

Cardboard Glue

Starch-based glue is most commonly used in cardboard production. The starch comes from food items like corn, wheat, potatoes, and rice and is 100 percent safe.

Ink On Printed Cardboard

Cardboard printing may use either vegetable dyes or colored inks. Vegetable dyes come from plant parts like tree bark, leaves, roots, and berries. On the other hand, colored inks contain heavy metals and can be a concern.

A study done in Canada shows that soil can have 13 to 750 mg of lead per kilogram. Compare that to 2.6 mg per kilogram in recycled cardboard.

With such a small amount, you'll need piles of composted cardboard to significantly raise the lead value of most soils to be harmful.

That said, we can see that cardboard is safe to use in organic gardens. The chemicals of concern pose little to zero risk when used in gardens.

What Type Of Cardboard Can I Use For My Garden?

Brown corrugated cardboard is best for use as they contain the least chemicals. Remove staple wires, tapes, and stickers from cardboard before use.

You'll want to avoid using waxed cardboard because the wax may harm the soil. Also, avoid using cardboard with a lot of colored print because the coloring may contaminate the soil.

See these cardboard sheets on Amazon.

Different Ways To Use Cardboard In Your Yard

You can use cardboard in many ways in your garden. Working with cardboard is favorable because it is a compostable material readily available.

Here's how you can use cardboard in your garden:

For Sheet Mulching

person rolling soil on cardboard add

Sheet mulching or lasagna composting using cardboard is an effective and inexpensive way to prep your garden beds for planting. In fact, by using cardboard, you're adding organic matter and increasing the nutrient level of your soil.

Another plus in using cardboard is it attracts earthworms. Increased earthworm movement certainly aerates the soil. Earthworm manure is a natural fertilizer and improves soil conditions.

When you've picked your garden spot for mulching, cover the area with cardboard and put your compost on top of the cardboard. Lastly, add wood chips and other organic materials for mulching.

Use As Compost

For making compost, you'll need both brown and green organic matter. The ratio for this is 25:1. Cardboard certainly counts as brown matter.

Soak and shred your cardboard and mix it with the organic matter. If you're using stiff cardboard, make it into a slurry before you add it.

Effective Weed Control

Cardboard is a good, natural alternative to using herbicides to kill weeds. Using cardboard to control weeds is most effective during the early stages of weed growth.

The cardboard sheets are an excellent alternative to landscape fabric and can last up to 2 seasons.

The process is easy. Lay pieces of cardboard over weeds to smother them and deprive them of sunlight. Place rocks or heavy objects on top of your cardboard to weigh it down.

Use As Starter Pots

toilet paper roll recycled seedling planters

Don't throw away those cardboard toilet paper cores. They make good seedling starter planters.

Cut slits on the bottom of your toilet paper roll. Then, fold the ends of one side, fill them with soil, and plant your seeds. When it's time to transplant the plants, you may plant them in the garden, including the toilet paper core.

For Cardboard Herb Gardens

You can start a cardboard box herb garden with different-sized boxes. Fill boxes with soil, plant your herbs and place them indoors or on a windowsill.

Then, when you need your herbs, you'll have them fresh and handy!

Plant Protectors

Some plants need protection from frost when they are freshly sprouting. Cardboard boxes are a good choice because you can create them according to the size of the plant.

Pick a box that can cover the entire plant. Leave some clearance between the plant and the container. You can use stakes to keep the box in place if there's a strong wind.

For Square Foot Gardening

Square-foot gardening is a gardening method that creates gardens in small spaces. Twine is usually used to divide space 4 feet by 4 feet into 1-foot squares.

You can make a square-foot garden using the same size cardboard boxes and placing them side by side.

For Creating A Pathway

You can use cardboard as the foundation of your garden pathway. Lay out the cardboard to the shape of your path. Cover the cardboard with soil and pebbles and outline it with rocks or bricks.

Should I Wet Cardboard Before Adding It To A Compost?

Yes, you need to soak your cardboard in water before composting. Your compost mix needs 40 to 60 percent water to hasten the decomposition process.

How Long Does It Take For Cardboard To Decompose In Soil?

straw cardboard being used sheet mulching, Is Cardboard Safe For Organic Gardening?

Smaller pieces of cardboard will decompose faster because there is more surface area exposed to decomposers. Cut and shredded cardboard will start to deteriorate in 3 months.

Will Cardboard Break Down Over Winter?

The cardboard will break down over the winter. The fall is a good time to place your cardboard sheets for mulching. By the time winter is over, your cardboard will have decomposed, and you'll be ready for planting.

Will Roots Grow Through Cardboard?

Yes, roots can grow through cardboard. They will start growing through cardboard after three months.

Does Cardboard Attract Termites?

Termites are attracted to any plant-based products containing cellulose, including cardboard. When using cardboard in mulching, keep mulches away from the wooden slabs of your house.

To Finish Up

straw cardboard being used sheet mulching

Using cardboard in your garden can be a way to cut down on gardening costs, and it's perfectly safe! Brown, corrugated cardboard is best for use in organic gardening.

Remember to clean your cardboard before using it by removing tape, stickers, and staple wires.

And while we have your attention, check out these related articles!

How To Compost Garden Waste At Home

Will Bulbs Grow Through Cardboard?

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