Is Cardboard Safe to Use in the Garden?

You may have seen gardeners use cardboard as mulch or to suppress weeds, but is it safe? Join organic farmer Jenna Rich as she dives into this interesting option.

Written by Jenna Rich Horticulture review by Sarah Jay Last updated: May 1, 2024 | 2 min read

Using cardboard safe for garden. Close-up of a gardener wearing large yellow gardening gloves rolling wet soil into cardboard. The soil is moist and lumpy.

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I bet we all have areas of our garden with persistent weeds or creeping grass. If you’re an organic gardener, weed killer is out of the question, so what to do? How about repurposing those delivery boxes into an eco-friendly weed barrier? I’ve seen cardboard help open up new garden plots, keep pathways clear of weeds, and smother weeds around newly transplanted perennials.

Last year, we surrounded our newly transplanted raspberry bushes with cardboard, added a heavy layer of woodchips to weigh them down, and then ran our irrigation drip lines over them to wet them, ensuring they stayed in place. It allowed the shallow-rooted plants to become established without being bothered by the stubborn grass and pesky weeds. We’ll add another layer this year.

If you have been saving your delivery boxes for a rainy-day project, I’ve got an idea for you. Let’s talk about when, why, and how to safely use cardboard boxes in the garden.

Short Answer

Yes, cardboard can be safe to use in the garden, but there are a few things to consider before covering your whole garden in it, like the source of the box, what it was used for, and a few possible disadvantages. There are lots of folks out there using cardboard with much success, and you can too.

Long Answer

Repurposing cardboard on farms and gardens has been a popular method in the no-till growers’ world for many years. It’s an eco-friendly way to repurpose delivery boxes that Jesse Frost, farmer and author of The Living Soil Handbook swears by.

Before putting cardboard in your garden, there are a few things to consider. Let’s talk DOs and DON’Ts, advantages and disadvantages, and some creative ways to use it.

The Right Stuff

Close-up of two cardboard boxes on the path in the garden. Cardboard boxes feature a rectangular prism shape, constructed from sturdy, corrugated cardboard material.

Do use cardboard that:

Indicates it’s 100% compostable and safe.
Has no remaining packing tape. Tape will not break down, so it’s important to remove it before using the cardboard.
Features plant-based ink.

Do not use cardboard that:

Has a glassy, exterior wax coating. This includes food delivery containers from pizza restaurants that are specially designed to keep moisture out and may cause issues. The coating may hold onto moisture under the soil surface, causing rot and damping off of plants.
It has been used to package raw meat. This is important for sanitary and possible contamination and leaching issues that could occur.
Is colored or has artificially dyed ink on it that can leach into the soil.

Advantages of Cardboard

View of a raised wooden vegetable garden filled with a layer of cardboard in a sunny garden. The raised bed is made of wood, covered with a layer of cardboard sheets. Next to the raised bed are beds of cabbage vegetables growing. — Cardboard blocks weeds, enriches soil, and attracts beneficial earthworms.

Here are some benefits of using the right type of cardboard:

Cardboard is effective at blocking the sun from the soil surface, which can prevent weeds from germinating. It can also help smother out unwanted plants.
It’s made from natural materials and will break down easily, adding food and fertility to your soil.
Earthworms are attracted to the dark space underneath cardboard. As they travel up through the soil, they’ll create tunnels that help with soil aeration. It’s thought they might also be attracted to the microbes that are feeding on various leftover food or juices left on the cardboard, that is if the boxes were used to transport food or possibly the plant-based glue used to construct the boxes. Plus, castings left behind are extremely beneficial to long-season crops like peppers, tomatoes, and eggplant.
Cardboard is more environmentally friendly and easier to work with than large plastic tarps.
It may help your soil retain moisture.
It can help control erosion on sloped land.
Adding a layer of cardboard beneath your expensive compost makes it last longer by holding it in place instead of sinking into the soil.
It’s free and easy to come by!
Plant roots can’t grow through it and get tangled up the way they do in landscape fabric.

Disadvantages of Cardboard

Close-up of dark brown soil scattered on a layer of cardboard sheets in a sunny garden among grass. The cardboard sheets are slightly damp. — While cardboard has its drawbacks, proper usage outweighs its disadvantages.

Cardboard can be useful for your garden, but there are some disadvantages, too. Here are a few:

It may attract mice or voles, who may start a family under the protection and darkness. Southern gardeners may attract roaches and Palmetto bugs.
It may be slippery to walk on before it begins to break down. Pro tip: Pair it with a secondary mulch like leaves, woodchips, or bark to help keep it in place.
Because it breaks down so quickly, you’ll have to reapply year after year. Have a long-term plan before adding cardboard.
If used too heavily, it may smother the soil and interrupt the natural gas and water flow between air and soil, which may disrupt the activity in your soil.

When used properly, in moderation, and not too heavily, the advantages of using cardboard outweigh the disadvantages.

How to Use Cardboard

Close-up of a corn bed with soil mulched with cardboard sheets. The corn bed presents a captivating sight with rows of tall, vibrant green stalks standing in uniform formation, reaching towards the sky. — Utilize cardboard for weed suppression and garden improvement effortlessly.

Now that we know why using cardboard can be easy and effective, here are a few creative ways to use it:

In the lasagna mulch method, layered with mulched leaves and compost.
For early-season weed suppression. Add it around the edge of your garden plots to keep stubborn grass from creeping in and keep it looking tidy, or lay it over the top of prepared garden beds until you’re ready to sow seeds or transplant.
To help open up a new garden plot by killing back grass or weeds. If you have a tarp, lay this over the top to add heat and jumpstart the microbial activity and die-back of the new plot.
In garden pathways. Pro tip: Wet the cardboard before laying it down, and then cover it with straw or woodchips to keep it in place. The water will also kick off the breaking down period.
Leaving soil bare is just asking for trouble, so if you find yourself with some underutilized land that’s already been opened up, lay down some boxes and layer on some mulch or a tarp to buy yourself some time.
Practice the Back to Eden gardening method to improve your garden’s health, soil composition, and fertility in time.

You’ll find after a while that you prefer certain styles and brands of boxes that fit perfectly in your garden setup. Until you find that Goldilocks box, use a sharp box cutter to cut them along a seam to the size you need. Overlap the pieces by a few inches.

So, Should You Use It?

Close-up of a garden plot with cut grass, half of which is covered with cardboard sheets. The grass is dry, green-gray in color. The cardboard sheets are rectangular beige-brown sheets from disassembled boxes. — Experimenting with cardboard in gardening is both personal and sustainable.

As with everything in gardening, using or not using cardboard is a personal preference. If you choose to use it, experiment with different application methods and timing, taking notes on the results.

Repurposing cardboard boxes is another way to live more sustainably and improve your soil health simultaneously. Here are just a few other creative ways of using cardboard in and around your gardens:

As a sturdy surface for seed-starting areas. Bonus: The cardboard will retain moisture and keep your seedlings from drying out.
Beneath backyard chicken coop bedding.
On the floor of your outdoor greenhouse to suppress weeds and soak up moisture.
Tear it up and add scraps of it to your compost.
Add some beneath compost around the base of a newly transplanted fruit tree.
Stack pieces of box trimmings to wedge a greenhouse door or level a work table.
Cover your soil station with cardboard to keep it from drying out.
Place cardboard over your garden beds in the fall with some weight bags for a weed-free and tidy spring.
Cut cardboard boxes into smaller boxes and use them as biodegradable planting containers. Open the bottom or poke holes in it before planting to make it easier for the plant to set roots. The box should break down within a few months.
Planning to ditch the turf and start a wild yard? Cardboard boxing your grass will help you start this process.

The possibilities are endless and boxes seem to be infinite in today’s world. If you aren’t an online shopper, grab some boxes at your local grocer or food co-op.

Final Thoughts

With the right type and proper methods, cardboard is safe to use in the garden. Ensure it’s clean and environmentally friendly before tossing it down, and remember it’s most effective when layered in some way.

I find new ways to use boxes every season, so it’s great to have them lying around. I hope you’ve discovered a few ways to utilize cardboard boxes in your garden. Here’s to weed-free and fertile gardens!