Cardboard Mulch: Everything You Need to Know

Cardboard has been utilized as mulch since the 1970s. It’s pretty easy to see why—most of us have a lot of leftover cardboard, so why throw it away when you can recycle it? Cardboard mulch is one of the cheapest and easiest options for an at-home, DIY gardener.

I recommend using cardboard that doesn’t have any plastic or duct tape on it. To help the cardboard degrade more quickly, either use long strips of cardboard or cardboard that has been shredded. Additionally, watch out that the cardboard mulch does not come into direct contact with the stem of your plants—this can harm your plants.

Interested in reading more about mulch? We have complete guides about the benefits and disadvantages of red mulch, cedar mulch, rubber mulch, and newspaper mulch!

Old cardboard that could be used for mulch
Thousands of pounds of cardboard go unused each year.

Why Use Cardboard Mulch? 

Cardboard mulch excells at smothering weeds. By blocking the weed’s access to light, it causes them to wither away under the cardboard. This works especially well on weeds like clover and chickweed that are soft and lack runners.

Cardboard has air spaces between its layers and is made of high carbon content. This enables bacteria to enter and begin decomposing the cardboard in your soil. Bacteria and cardboard will attract worms, which will accelerate the decomposition process.

Finally, cardboard has the same nutrients that cedar mulch has. Although it disintegrates quicker, it provides the same benefits to the soil and dirt.

Cardboard boxes being thrown out

How to Make Cardboard Mulch? 

Pick Your Cardboard 

Food pulp can be compared to ready-to-use mulch because it is used to produce cardboard. The nutrients in cardboard mulch are the same as those in wood chip mulch. However, the rate of decomposition of cardboard differs greatly. Due to the manner it is created from wood pulp, cardboard frequently decomposes rather quickly once it has been moistened.

Plastic-coated cardboard mulch is the last thing you want in your garden since it will prevent water from penetrating the soil and eventually cause it to dry out. Because the glue from the duct tape doesn’t mix well with the soil and the duct tape won’t actually disintegrate, be careful to remove it from the cardboard.

Shed The Cardboard 

When you have some cardboard, it’s time to use it as mulch, but first, you must choose whether to use whole pieces or shredded cardboard. Although larger pieces of cardboard typically do a great job of suffocating weeds, they will degrade more slowly than shredded cardboard. Use the cardboard that works best for you; if you have a larger garden, it will be easier to mulch with larger pieces than with shredded ones.

Put Cardboard Mulch Around Your Plants 

Make sure the cardboard mulch is placed around your plants so that the mulch doesn’t really contact the plant stem. Wood pulp, used to make cardboard, contains a lot of nitrogen, which is excellent for plants but may also be harmful if consumed in excess. Ensure that the cardboard is not in direct contact with your plants because too much nitrogen could burn their roots and stems.

Layer the Mulch 

Depending on your cardboard type, you should layer the cardboard mulch thickly or thinly. One layer of these should be sufficient if you use large pieces of cardboard; some of them may probably overlap, but that shouldn’t be a major issue. If you are utilizing huge cardboard pieces, avoid stacking them on top of one another in multiple layers since this will cause more damage than good.

If you do this, the soil above the mulch will deteriorate in a few months since the top layer will begin to dissolve because it can absorb water. Still, the bottom layer will eventually dry out if it doesn’t get enough water. A 2 to 5-inch layer of chopped cardboard should be plenty of mulch. Some people use a thicker layer, which is also acceptable, but try to avoid layering it too thinly.

If you’re looking for topsoil to put on top of your cardboard mulch, I recommend using Minute Soil!

Water the Mulch 

It’s time to moisten your cardboard mulch after you’ve stacked it. Watering the cardboard mulch will make it heavier and less likely to be blown away by the wind as the cardboard absorbs water. Additionally, the extra moisture will hasten the breakdown process. If you have a sizable garden, you might wish to sprinkle the cardboard before spreading it out; I assure you that doing so will make it much simpler to work with.

Add Additional Mulches 

In most cases, individuals combine cardboard with other mulches for aesthetic reasons. Frankly, cardboard mulch just isn’t that attractive. Grass and wood chips are the most frequent mulches used on top of the cardboard mulch layer, and both are quite effective. Use wood chips if the appearance of the mulch in your garden is more important to you.

Grass, hay, straw, and other materials that decompose quickly should be added to the cardboard if you plant annual plants. Wood chips also decompose, but it takes much longer for the nutrients they contain to reach the soil.

Final Thoughts 

As you can see, mulching with cardboard is really simple. All you have to do is choose the proper cardboard and layer it around your plants so that the mulch doesn’t touch the plant stem. Ideally, you should also water the mulch because it will be much simpler to handle, especially on windy days.

Interested in reading more about organic gardening? Check out our library of free resources!

How to make cardboard mulch

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