Using Cardboard in the Garden

Using Cardboard in the Garden

If you love online shopping, you probably have a LOT of extra cardboard around. While it’s recyclable, it’s also easy to repurpose around the garden! Using cardboard in the garden can save you money by replacing some common gardening purchases, as well.

We’ve gotten creative this year with using cardboard in our garden, particularly for trying to keep weeds down. There are so many options depending on your gardening needs! Here are a few, along with some guidelines for getting started:

Types of Cardboard

First, you’ll need to gather the right kind of cardboard for your garden. Skip the product packaging, like cereal boxes. Waxy cardboard, like some pizza boxes, won’t work for any area that you want to still receive rainwater, so in general avoid using those as well. You want as plain a corrugated cardboard as you can get – like the boxes that come from Amazon.

Remove any tape that won’t decompose, along with labels. Break the boxes down to single or double layer thickness when you want sheets, or leave them intact for some of the projects below.

Use #1: Cardboard Weed Barrier

Perhaps the easiest way to use cardboard is by making a simple cardboard mulch to use as a weed barrier.

Cardboard for Weed Control

Before planting seeds or transplanting seedlings, mark out your row or dig your holes. Then cut the cardboard to the appropriate size for your row (or cut large holes out of the cardboard) based on the space that will be left between plants. You want the plants to still have some dirt showing, so consider how large they will get once mature and leave several inches beyond that.

Add the cardboard and place a few rocks or other weights on top to hold the cardboard down. Plant seeds or transplants in the remaining spaces, and then relax – you’ll have significantly fewer weeds to contend with this growing season! (Here’s a weed identification guide.)

Additionally, in fall, you can lay sheets of cardboard down over your vacant garden areas so that weeds won’t start growing first thing in spring before you start planting.

How Long Does Cardboard Weed Barrier Last?

Depending on the cardboard’s thickness and the time of year, you can expect your cardboard to effectively block weeds for 3-6 months. While that may not seem like a long time, it will still be somewhat effective for several months after that, and you can always layer more cardboard on top if it stops working!

#2: Making Footpaths

Place flat strips of cardboard anywhere where you want a footpath between raised beds, garden sections, and more. While the cardboard can make it a little slippery at first, the boxes will break down and become more textured. You can also cover the cardboard with pavers or another type of mulch, like wood shavings, to make it look a little nicer and make it less slippery. You’ll have clearly lined paths and not have to deal with the weeds rubbing your legs!

#3: Retain Moisture

If your plants are moisture lovers or dry out quickly, you can use cardboard in several different ways to help retain moisture.

First, you can place it under potted plants and seedlings to help capture moisture at the bottom. This will not only help keep the water from draining out everywhere, but it will hold the moisture so the plants can use it again later.

For plants growing in the garden, you can follow the steps for cutting and arranging the cardboard for weed suppression above, and it will also help retain moisture directly around the plant.

#4: Cardboard as Garden Filler

If you have large planters or a raised bed, you can use cardboard as a filler. Lay sheets of it in the bottom of a raised bed (the cardboard will double as a weed suppressor!). For potted plants, cut strips and use them in the bottom of large planters. This will save you from needing as much potting or gardening soil.

#5: Cardboard Garden Planters & Starter Pots

You can use cardboard boxes as planters for your vegetables. Since the cardboard will last approximately the same amount of time as the plant’s growing season, you can just toss the whole thing in the compost pile when you’re done.

Cut holes in the bottom of your box for extra drainage, and set it on a platform of rocks, cement blocks, or another porous material to keep the bottom of the box from prematurely decomposing. The box can be moved early on, but plan to keep it in one place by the middle to end of the plant’s growing season. By that time, the cardboard will have weakened and the weight of the plant may cause the box to break.

If you have small boxes with fun designs or interesting material, you can also use them as cheap planters for your flowers. You can even paint them or cover them for a more interesting look, just remember that they’ll probably only last one year!

Try using a thin, flimsy cardboard for plants that resent transplanting – small boxes, toilet paper rolls, paper towel rolls, and any other plain, thin cardboard can work. Start the seeds in the boxes or rolls, then plant them, cardboard and all, in their final home.

#6: Using Cardboard for Tree and Plant Protection

There are some great ways to use cardboard to help protect and support certain plants and trees.

For small plants, you can ring the stem with the cardboard insert for toilet paper or paper towel rolls. My grandmother always used toilet paper rolls around young broccoli to support the growing stems and prevent bugs.

For young trees, you can cut large pieces of cardboard and wrap them loosely around the trunk. Secure with twine or tape, and leave for the season to help prevent bugs, deer, and more from hurting the growing trunk.

#7: Frost Protection

For tall or weak plants that you don’t want flattened by a frost cover, you can flip over a cardboard box to use as a cover instead of a bucket. The thicker the cardboard, the better, as it will better preserve the heat coming back from the ground and defend against the cold. (Here’s a whole post on frost protecting your garden.)

#8: Cardboard Storage Boxes

My other favorite way to use cardboard in the garden is to use the boxes for storage! You can store your seeds in one, use another as a toolbox, and even overwinter various plants with them. In particular, I like to use open boxes to store root vegetables and bulbs overwinter.

#9: Compost Additive

Since cardboard decomposes, you can just add it to your compost pile. It adds valuable carbon that the compost pile can benefit from. Plus, worms and other decomposers love cardboard!

#10: Developing New Garden Spaces

In the same way it can block weeds, cardboard can block all plants! If you want to expand or add a garden or flower bed, lay overlapping cardboard down over the area to kill off all the plants. Secure the cardboard with rocks and water the area. You can add another mulch, like hay or compost, on top if you’d like. After a few weeks, the plants will be mostly dead and the area can be worked up.

This sheet mulching, as it’s called, can most effectively done in late summer and early fall, so that by spring you can peel it off or cover the cardboard with more dirt and start preparing your new garden area.

Happy Cardboard Gardening!

As you can see, there are many ways of using cardboard in the garden! Try a few and see what works best for you and your plants.