Can You Grow Plants In A Cardboard Box? (6 Ways To Use It)


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 often for free), so it makes sense to consider it for your garden.

So, can you grow plants in a cardboard box?  You can grow plants in a cardboard box – you just need to find one of the right size.  With this method, you can transplant the box and plants into your garden and let the cardboard decompose.  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.

Of course, there are lots of benefits when growing plants in a cardboard box. There are also lots of other uses for them in the garden.

In this article, we’ll go over why you should consider planting in cardboard boxes. We’ll also look other uses of cardboard, along with the best way to compost it and where you can find it.

Let’s get started.

Can You Grow Plants In A Cardboard Box?

You can grow plants in cardboard boxes, as long as you can find one of the right size for your plants.

cardboard boxes
Cardboard boxes can make a good tray for starting seeds.

There are lots of good reasons for planting this way:

  • Cardboard boxes are much lighter than clay, ceramic, or concrete pots. This makes them much easier to move around when you transplant seedlings from your house to the garden.
  • You can put cardboard boxes directly in the soil, since they will decompose with the help of bacteria and worms.  After they are broken down, the cardboard boxes will provide food and organic material for plants.
  • Cardboard boxes come in lots of different 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.
  • 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.
pumpkin seedling
You can plant seedlings directly into the soil in your garden, without removing them from a small cardboard box!

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.

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.

A piece of wood or metal could also serve the same purpose. A seed tray is another option for supporting a cardboard box that may be flimsy due to water and soil.

aluminum trays
An aluminum catering tray could be used to hold a cardboard box that is soggy and falling apart.

When you want to move the box, move the plastic, wood, or metal 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.

roots
Plant roots will grow through cardboard as it breaks down. This happens faster in wet soil with lots of bacteria and worms.

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.

earthworm
Earthworms will help to break down cardboard faster.

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.

On the other hand, if you want to lay cardboard on the ground to prevent weeds from growing up, it should prevent their growth. Just be sure to use a thick enough layer of cardboard, and replace it when it starts to break down.

A layer of cardboard can also prevent grass from growing, on smother existing grass. This is useful if you want to expand your garden!

aged manure on cardboard on grass
Using aged manure or compost to weigh down cardboard holds it in place while it smothers grass to make a new garden area.

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 & Prevent Weeds

Cardboard boxes make a great ground cover if you want to kill existing weeds or prevent new ones from growing. The University of Maryland Extension suggests that a layer of cardboard can also be used to smother grass if you want to make it easier to expand your garden.

weeds
Cardboard can smother weeds or prevent new ones from growing.

A plant grown in or above cardboard may eventually be able to break through cardboard as its roots grow. However, a plant usually cannot grow up through cardboard from below.

The reason is that a layer of cardboard over a plant prevents air and light from getting through, both of which are necessary for growth.

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 can 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 can find more alternatives to wood mulch in my article here.

cardboard boxes
Use crushed cardboard as mulch in your garden.

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. This will prevent any stray weeds from poking up through a small opening.

Use Cardboard Boxes To Line Raised Beds

You can use crushed cardboard boxes to line the bottom of raised beds to prevent weeds. You can also use cardboard boxes to bring some order to your raised bed gardening.

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 keep the plants in their own “zones” and prevent them from competing with one another.

wooden raised garden bed
You can use cardboard to separate different plants in a single raised bed.

For more information on other materials you can use as liners, check out my article on lining raised garden beds.

Use Cardboard Boxes To Start Seeds

If you have a bunch of small cardboard boxes, you can use them as containers to start individual plants from seed.  If the germination rate of the seeds is low, you can plant 2 or 3 seeds per small box.

After the seeds germinate, you can thin them to the strongest seedling if more than one seed germinates. You can learn more about thinning seedlings in my article here.

pumpkin seeds
You can start your seeds in small cardboard boxes and then plant the entire box in your garden after the last danger of frost has passed.

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 for your plant!)

You can also arrange several small boxes inside a larger cardboard box or plastic bin. Then, you can 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 Pest Damage

Pests are another hazard for your plants, but cardboard boxes may be able to help with that too. For example, it is easy to use a long piece of cardboard to make a plant collar.

All you need to do is roll the cardboard into a circle so the ends meet. Then, tape or staple the ends together and put the collar around your seedlings after transplant.

This will stop cutworms and other pests from cutting down plants before they have a chance to grow.

cutworm
A cardboard plant collar can prevent cutworms from damaging plants.

You can also make plant collars out of other materials – for more ideas, check out my article on making plant collars.

Use Cardboard Boxes To Prevent Disease

Another idea is to use pieces of cardboard to put up a shield around your plants. This will stop rain from splashing soil up onto the leaves of plants.

This will keep your plants healthy, since infected soil on plant leaves is a major cause of disease spreading through a garden. For example, fungal spores that cause blight can spread when wet soil splashes around.

Use Cardboard Boxes To Insulate Plants From Cold

You can also use a cardboard box to insulate plants from the cold. This is especially useful if you are worried about late spring frosts or cold nights.

frosted leaf
Use cardboard to hold up a row cover or frost blanket.

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 that will keep it dry
  • the cardboard is either buried underground or in direct 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 job to break it down quickly.

cardboard boxes
Cardboard that is covered with wax or plastic will not break down as fast as unprotected cardboard.

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 You Compost Cardboard?

You can compost cardboard, since it is an organic material that comes from wood (just like paper). Cardboard is good for plants after it has decomposed, since it will add organic material to the soil.

cardboard box
Cut your cardboard box into small pieces so that it will decompose and turn into compost faster.

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.
  • Next, break the cardboard box into pieces by cutting along the edges, and then tear it up smaller if you wish.
  • Then, 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.
compost bin
Add some grass clippings to the cardboard in your compost pile to balance greens and browns.

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 has colors or writing on it may contain 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.

The Oregon State University Extension suggests that you avoid using advertising inserts.

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.

Conclusion

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.

You might also want to read my article on growing plants in a can.

I hope you found this article helpful – if so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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