You may have heard of clay pots, plastic containers, or grow bags for growing plants, but have you ever thought about using cardboard? You can find cardboard in abundance, and usually for free, so it makes sense to consider it for your gardening.
So, can you grow plants in a cardboard box? Yes, you can grow plants in a cardboard box. With this method, you can transplant the box and plants into your garden and let the cardboard decompose underground. You can also compost the cardboard or use it as mulch (ground cover) for weed control. You can get free cardboard boxes from restaurants, retailers, or wholesale clubs.
There are lots of benefits of growing plants in a cardboard box, and there are lots of other uses for cardboard in the garden. Let’s go over some of these in more detail, along with the best way to compost cardboard and where you can find cardboard.
Can You Grow Plants In A Cardboard Box?
You can grow plants in cardboard boxes, and there are lots of good reasons for doing so.
First of all, cardboard boxes are much lighter than clay, ceramic, or concrete pots, meaning that they are much easier to move around. This makes things simple when you want to transplant seedlings from your house to the garden.
Of course, you can still use clay or plastic pots if you want – they both have their uses. For more information, check out my article on clay versus plastic pots.
Also, you can put cardboard boxes directly in the soil, since they will decompose underground with the help of bacteria and worms. In this way, the boxes will provide food and organic material for plants.
In addition, cardboard boxes come in lots of sizes, making them versatile and easy to fit to your purposes. You can use small boxes for growing individual plants, or larger boxes for starting an entire packet of seeds.
Finally, cardboard boxes are easy to arrange, since they are all rectangular and will fit together nicely if you decide to use multiple boxes to plant indoors.
However, there is one caution about growing plants in cardboard boxes. When you water your plants, the soil will get wet, and some of this moisture will seep into the cardboard.
Over time, the cardboard will get soggy and weak, especially at the bottom. This can cause the box to collapse under its own weight, spilling your soil everywhere.
If you try to move a soggy cardboard box with a plant in it, the bottom may drop out and spill your soil, along with your plant. To prevent this, avoid moving your boxes right after watering.
A good alternative is to put something underneath the cardboard box to reinforce the bottom. For example, a long, flat piece of plastic is a good choice, since it will not get soft and it will resist mold if it gets wet.
When you want to move the box, move the plastic with it to prevent the bottom from dropping out.
Can Plants Grow Through Cardboard?
When planted in a box, a plant’s roots may break through cardboard if there is nowhere else to go for water and nutrients. Before doing that, however, the roots will probably spread out horizontally or vertically before growing through cardboard.
After repeated watering and decomposition due to bacteria and worms, the cardboard box will probably break down to the point where a plant’s roots can break through it easily.
If you know that your plant’s root system will quickly outgrow the cardboard box, you can take the following step to make things easier for your plant.
Before you bury the box in the ground, poke some holes in the bottom and sides. That way, the plant’s roots have an easy way to escape from the box.
Other Uses of Cardboard
There are other uses for cardboard boxes besides as containers for plants. One of my favorite uses is as a weed killer or suppressant, so let’s start there.
Use Cardboard Boxes To Kill and Prevent Weeds
A plant’s roots may eventually be able to break through cardboard, but a plant cannot usually grow up through cardboard. The reason is that a layer of cardboard over a plant prevents air and light from getting through.
It also gets very hot underneath the cardboard, and combined with the lack of air and light, this makes life very difficult for weeds. If you already have weeds in your garden, you lay some flat cardboard over the weeds to cook or suffocate them.
Even without any weeds, you can still lay down a layer of crushed cardboard boxes as mulch on top of your soil. This will prevent old weed seeds from sprouting in the soil, and it will prevent new weed seeds from getting into the soil at all.
You can also lay down some grass clippings, raked leaves, or some other type of mulch on top of your cardboard boxes if you wish.
You have the option of crushing your cardboard boxes to lay them flat, or cutting them into rectangular strips along the edges.
Either way, you should lay the cardboard strips two or more pieces thick, with some overlap between pieces, to prevent any stray weeds from poking up through a small opening.
Use Cardboard Boxes To Line Raised Beds
You can also use cardboard boxes to line raised beds.
For instance, if you have a large raised bed, you may want to grow more than one type of plant in it at the same time. You can use separate cardboard boxes to segregate the plants and prevent them from competing with one another.
For more information on other materials you can use, check out my article on lining raised beds.
Use Cardboard Boxes To Start Seeds
If you have a bunch of small cardboard boxes, you can use them containers to start individual plants from seed. If the germination rate of the seeds is low, you can put 2 or 3 seeds per small box, and thin them to the strongest seedling if more than one seed germinates.
This method is great because you can transplant the seedlings directly into the soil in your garden – cardboard box included. Over time, the cardboard box will decompose and provide nutrients and organic material for the soil (and thus for your plant!)
You can also arrange these small containers inside a larger cardboard box or plastic bin to move them all at once to your garden for transplanting.
Of course, some seeds may need higher humidity levels for germination than a cardboard box can provide. For more information, check out my article on humidity domes.
Use Cardboard Boxes To Prevent Disease
If you use pieces of cardboard to put up a shield around your plants, you can prevent rain from splashing soil onto the leaves of plants. Avoiding this will keep your plants healthy, since infected soil on plant leaves is a major cause of disease spreading through a garden.
Use Cardboard Boxes To Insulate Plants From Cold
You can also use a cardboard box to insulate plants from the cold, especially if you are worried about late spring frosts or cold nights. This would work something like a cloche, but made of cardboard instead of plastic or glass. For more information, check out this article from growveg.com on using cardboard in the garden.
How Long Does It Take For Cardboard To Decompose In A Garden?
Under ideal conditions, cardboard can decompose in your garden in a few months. This is what I mean by “ideal conditions”:
- the cardboard is not covered with any wax, plastic, tape, or other protective materials
- the cardboard is either buried underground or in contact with the soil
- the cardboard is exposed to water, either above ground or underground
If your cardboard is covered with wax or plastic, it won’t get as wet, and it will take longer to decompose. If the cardboard is not in contact with soil, bacteria and worms won’t be able to do their jobs to break it down quickly.
To make your cardboard decompose faster, wet it and mix it with some “greens”, such as grass or other high-nitrogen organic matter. Keep it wet and it will break down much faster.
On the other hand, if you want to make your cardboard boxes last longer, you should use plastic bags or sheets to line the inside and outside of the box. This will prevent rain, watering, and sunlight from speeding up the decomposition of the box.
Can I Compost Cardboard?
Yes, you can compost cardboard, since it is an organic material that comes from wood (paper). There are some steps you can take to speed up the process of turning your cardboard into compost.
First of all, remove all tape, glue, plastic, and other inorganic materials from the cardboard box. Then, break the cardboard box into pieces by cutting along the edges, and then tearing it up smaller if you wish.
After that, make sure to wet the cardboard thoroughly to get a good start to the decomposition process. Finally, lay the cardboard on the ground so that one side is in contact with the soil, and cover the other side with some “green” organic material, such as grass clippings or leaves pruned from plants.
For more information, check out my article on how to make compost.
Is It Safe To Compost Cardboard?
If you are worried about the contents of your cardboard, it is wise to check the source before you put in in your garden or compost pile.
I suspect that cardboard boxes from restaurants are food-safe if they were used to ship fruits or vegetables. However, this may not always be the case, so you should ask if they were treated with anything that you might not want in a garden.
Cardboard that is colored or that has writing on it may have ink that you don’t want in your garden, so ask the manufacturer about the nature of the ink used for printing on the boxes.
Recycled cardboard boxes are usually treated with chemicals, but a process is used to remove any metal and plastic, such as from staples or tape. For more information, check out this article on cardboard recycling from conserve-energy-future.com.
Where Can I Get Cardboard Boxes?
There are plenty of sources for cardboard boxes. You can visit wholesale clubs, retailers, and restaurants to ask about taking cardboard boxes. Usually, they need to find a way to get rid of or recycle these boxes, so they will be happy for you to take them away at no cost!
You can also friends and family for any extra boxes they have lying around, from cereal boxes to old shoe boxes.
Now you know that cardboard can be used to grow plants, and also for many other garden purposes. You also have some ideas on where to find cardboard so that you have a steady supply.
I hope you found this article helpful – if so, please share it with someone who can use the information. If you have any questions or advice of your own about growing plants in cardboard boxes, please leave a comment below.