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7 Ways to Use Cardboard for a Bigger and Longer Harvest

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Are you ready for a staggering statistic? In the United States of America, over 850 tons of paper and cardboard are thrown out each year. Sadly, this is equal to about 1 billion trees! Pretty horrifying, right?  Over 80% of the packaging used in America contains some form of cardboard. An average household can toss as much as 13,000 separate pieces of cardboard each year.

The good news is that much cardboard can be recycled and made into new products. In fact, there are many uses for cardboard in your garden that can save you money and help you reap a bigger and longer harvest. I love to get packages in the mail for two reasons – first, the contents of the package, second, the cardboard, which is truly a gift.

What type of cardboard can I use in my garden?

Cardboard, at its base level, is a form of paper and comes from trees. Because of this, it will break down, and when it does, it releases carbon into the soil. Carbon is a building block for life, and as it breaks down, it supplies much-needed energy for microorganisms, which improves soil structure.

Besides this huge benefit, there are many other benefits to repurposing cardboard in your garden. Let’s explore some of these now.

A word of warning

Not just any cardboard is safe to re-use in your garden. Cardboard with a lot of colored printing, tape, a shiny finish, or any cardboard that is white should not be repurposed. As a side note, Amazon Prime boxes use compostable tape, so this is ok. The best rule of thumb is to keep it simple – simple, plain brown cardboard works.

Using cardboard as sheet mulch

If you start a large garden from scratch, you know that there is a long list of foundational work that must be done first, such as weeding, digging, and amending the soil. Sheet mulching, also known as composting in place, is a great way to skip the heavy work of prepping a garden and improves soil quality at the same time – it’s a win, win. 

To use cardboard in the garden:

  • Use a mower to cut down grass/weeds to the lowest level possible.
  • Thoroughly water your garden plot.
  • Lay individual sheets of cardboard on top of the garden plot.
  • Put 4 inches of nutrient-rich compost on top of the cardboard.
  • Add 3 inches of additional mulching material such as wood chips or leaf mold.
  • Water the garden plot again, and you are ready to plant! I also use cardboard to line the bottom of my raised beds before planting.

Using cardboard to make a potato box

Potatoes are an easy crop to grow and even easier when you make your very own potato box. Since hilling potatoes is essential to safe growth, a potato box makes perfect sense. A sturdy medium-sized cardboard box works best. Keep the bottom of the box intact and add a few drainage holes. Fill the bottom with planting soil and plant your potatoes. As the green tops come up, cover them with more planting soil. When needed, slip another cardboard box over your initial box to create a growing tower. 

Using cardboard to make raised beds

If you are just getting started in gardening and don’t have a huge budget, consider using cardboard boxes as raised garden beds. Cardboard box-raised beds only last a season, but that buys you time to save money for something more permanent. Additionally, it gives you a chance to see whether or not raised bed gardening is for you. As an added plus, when the growing season is over, toss cardboard beds into the compost bin. Choose a sturdy box with enough depth and reinforce the bottom with compostable packing tape. Poke a few drainage holes in the bottom and fill the box with potting mix.

Using cardboard as a weed suppressor

Cardboard is not only great for building up soil structure, but it also makes an excellent weed-barrier. This makes me very happy because I don’t like to use herbicides in the garden and hate handpicking weeds. I lay cardboard pieces down around flowerbeds, shrubs, and trees. If you want to use cardboard up close to plants, make sure to cut a hole that is about 3 inches larger than the stem or trunk so that oxygen and water can still reach the plant’s roots. Most cardboard will last for a couple of seasons as a weed barrier before needing to be replaced.

Using cardboard for seed-starting pots

Using cardboard to make seed starting pots is not only environmentally friendly but also incredibly easy. I save my toilet paper and paper towel rolls, and when seed starting time arrives, I just need to get some potting soil, a tray, and some seeds. Cut the paper towel rolls in half or even thirds. Place the rolls in a 1-2-inch tray and fill with seed starting mix. Water from underneath, and once seedlings are strong enough, plant them directly into the garden, seed starting pot and all. The cardboard will decompose and help with soil structure. Consider arranging several boxes – each one-foot big – together to form a square foot garden.

Using cardboard in your compost

Compost piles require a proper balance between carbon materials and nitrogen materials. The best ratio I have found is 30 parts carbon to one part nitrogen. Cardboard, like dried leaves, straw, and wood chips, is a bulky carbon material perfect for adding to a compost pile. Before adding to your pile, shred the cardboard up into 1-inch pieces. Doing this will help speed up the decomposition process.

Using cardboard to protect young trees

Giving newly planted trees a little protection during the first several growing seasons is highly recommended – especially if you live in a colder climate. A tree guard helps protect young trees from frost and sun injury and deters critters who love to munch on the bark. I have tried several different types of tree guards including some made from plastic, metal, and burlap. Recently, I started using leftover cardboard to protect young trees and even some of my perennial plants.  

To make a spiral covering, cut cardboard in long lengths about 4 inches wide. Begin at the tree’s base and wrap the cardboard around the trunk by overlapping each layer about two inches. Keep wrapping until you reach the lower branches of the tree. Hold the wrap in place with garden twine. You can also make a freestanding tree guard by using a large piece of cardboard and bending it around the tree trunk. Keep the ends of the tree guard together using waterproof tape and make sure to leave a couple of inches between the guard and the tree trunk. As with other cardboard garden creations, tree guards will last just one season.  When you are finished with them, toss them into your compost bin.

I hope that the next time you are tempted to throw out your cardboard boxes, you consider giving them new life in your garden. Your garden and the earth will thank you.

Happy Growing,

-Susan, CBHC and Master Gardener

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