How to use cardboard in your garden: 6 ways to help plants, from enriching soil to preventing weeds

You've probably thought about the ways you can use cardboard in your garden, assuming its only destiny is for the recycling bin. However, it turns out there are many genius ways it can help keep your plants happy and healthy.

There's always more room for sustainable garden ideas and learning ways to reuse household waste will forever be a w&h favourite. From using teabags in the garden to learning how to utilise banana peels for plant health, our household waste is often our garden's treasure.

And cardboard is no exception as gardening experts have revealed five ingenious ways of using this disposable material for good in the garden, from getting rid of weeds to enriching soil.

How to use cardboard in your garden: 5 easy ideas

Whether you're a beginner in vegetable gardening or need help protecting your plants from frost, finding low-cost ways to make the process easier is always a good idea. So, if you're interested in trying some eco-friendly tips, here are all the effective ways cardboard can help improve your garden.

1. Alternative weed membrane

Aside from getting rid of weeds in the grass, most gardeners will also have to tackle how to get rid of weeds in vegetable patches and flower beds. Luckily, cardboard can be a great weed membrane alternative and can help prevent regular weeding.

"One of the main reasons people use cardboard in their beds and borders is because it makes a fantastic weed membrane," says garden designer and influencer Ish @Gardening.with.ish on TikTok."You’ll find that this will suppress any weed growth from coming up over the top."

Adding, "It does, however, break down which means over time the roots of the plant above it will grow through and hopefully prevent any more weeds from coming up top."

2. Water retention aid

With certain soil types, it can be a continuous struggle to keep your ground soil moist enough to keep the plants happy. This is especially important for flowers during the summertime, but using this water retention trick can help.

"Cardboard can soak in quite a bit of water so when it’s at the bottom of your beds and borders it can actually hold some of that moisture which means that your ground stays watered for longer," explains Ish.

He continues, "When that cardboard has decomposed you’ll think it’s a bit useless but actually the organic material in cardboard improves soil quality and can also improve drainage. Which is another fantastic benefit for a lot of flowers in the summer."

3. Protective insulation

Aside from protecting your garden from heavy rain, the UK weather always promises cold frosty mornings which aren't great for some of the more vulnerable outdoor plants.

Ish recommends cardboard as the perfect solution, "Cardboard works as a great insulating layer in cold frames, all of that cold ground temperature won’t rise into the cold frame and it’ll keep it warmer in there a little bit longer."

He explains how it works as a fantastic mulch alternative as well, helpful for protecting your flower beds and vegetable patches from cold weather and frost.

4. Compost enrichment

If you make your own compost you'll already know how great reusing household waste can be for providing nutrients – you might already be using orange peel in your garden for this very reason. Surprisingly cardboard is another great example of this.

"When you are composting, you will need to use more brown matter (e.g. paper, leaves) than green (kitchen scraps) to create compost," explains Graham Smith MCIHort, horticulture expert at LBS Horticulture. "Cardboard can be used as brown matter for compost, provided that it is broken down into smaller pieces."

As the cardboard breaks down it will also add its own nutrients that will elevate the compost even more, benefitting your plants.

Graham Smith MCIhort

Graham has extensive knowledge in the horticultural and gardening industries, and prides himself on using this to help gardeners of all skills create their perfect outdoor space.

5. Seed starter containers

One of the most rewarding parts of gardening is collecting seeds from your garden to sow them from the next year. Not only is it a sustainable way of growing plants but it's also an extremely affordable way too, especially if you reuse cardboard for your seedling trays – similar to

"Cardboard boxes can be used to start seeds, and you can leave seedlings growing inside of them for longer, giving you stronger seedlings. When the seedlings are ready to be planted, you can plant them while they are still in the cardboard, as it will break down in the soil," explains Graham.

You can also use egg cartons for seed starters, they provide the perfect-sized vessel and can be mulched or planted when the seedlings are established enough. You can even use eggshells in your garden to start seedings with a more protective casing.

Shop useful gardening tools

FAQs

Are there any places in the garden where you shouldn't use cardboard?

With any household waste, there are only so many places they can be used outdoors whilst still being beneficial. For example, when using coffee grounds in the garden, some acidic-loving plants won't react well to its pH. The same goes for cardboard, it won't work everywhere.

David Denyer, a professional florist and gardener says, "While cardboard is incredibly versatile, it's not perfect for every spot. Avoid placing it in waterlogged areas, otherwise, it’ll just turn into a soggy mess. Make sure you don’t use it too close to deep-rooted perennials—they need room to breathe, and too much cardboard can suffocate their roots."

David Denyer

As a celebrated figure in the world of floral design, David has captivated audiences with his stunning floral arrangements and designs for years. He is a two-time Florist of the Year and six-time Chelsea Gold Medalist, whilst also being the in-house plant expert for Eflorist.

What types of cardboard can you use and not use?

In the same way there are certain places in the garden where you probably shouldn't use cardboard, there are also different variations of the material to look out for.

"Not all cardboard is garden-friendly. Plain, brown corrugated cardboard is your best bet—with no harmful coatings, that could end up harming your plants. Avoid using anything shiny, glossy, or waxed—those coatings can leach harmful chemicals into your soil," advises David.

He also recommends removing any take or stickers from your cardboard before planting it, that way you're not digging up bits of plastic later down the line.

Why is cardboard particularly helpful in the garden?

It can be surprising the types of things that can be beneficial to our gardens. From using old towels to protect plants to reusing the skin of avocados for seedlings, there are several items we'd usually throw away that can be a great help to outdoor plants. But why is cardboard so useful?

David explains, "Its biggest benefit is its ability to kill off unwanted weeds, by blocking sunlight and preventing growth. As cardboard breaks down, it feeds your soil with organic matter; good for generating healthy soil for future plants. It also locks in moisture, so your plants stay happy longer between waterings."

Always make sure you check your cardboard before placing it down into your garden and within your soil. Any taps, stickers or printed areas can disrupt the pH of your soil and will of course not decompose like the rest of the brown material.