Mulching with cardboard is not a new trend, in fact, cardboard has been used since the late ’70s as mulch, and today as more and more people become familiar with mulching some of them choose cardboard as their preferred mulch. Most of us have a lot of extra cardboard, and why just throw it away if you can simply recycle it. This way you both cut down on your waste and you add back valuable nutrients to the soil as well.
You can mulch with cardboard by making sure to use cardboard that doesn’t have any plastic or duct tape on it. Either place large strips of cardboard around your plants or shredded cardboard and make sure to water it after, this way the cardboard will start to decompose a lot faster. In addition to this make sure the cardboard mulch is not in direct contact with the stem of your plants as the excess nitrogen could damage the plants.
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Cardboard is made out of food pulp, which means that cardboard is in fact dried out mulch ready to be used. Cardboard mulch has the same nutrients as wood chip mulch, but there is a big difference, cardboard breaks down extremely fast. Due to the nature of how cardboard is manufactured, from wood pulp, it tends to have a relatively fast decomposition rate once it has been watered.
There are a couple of ways of approaching mulching with cardboard, you can either use only cardboard as mulch, or you can add a layer of some other mulch. Grass clippings placed on top of the cardboard mulch is great, if you want to know more about mulching with grass then check out my recent article Mulching With Grass Clippings ( Top 9 Best Practices ).
Mulching With Cardboard
Using cardboard as mulch has proven to be an efficient and eco-friendly way to suppress weeds and improve soil health. By laying down sheets of cardboard on bare soil, I create a natural barrier that prevents sunlight from reaching weed seeds, hindering their germination and growth. The thickness of the cardboard also helps conserve moisture in the soil, reducing the need for frequent watering.
As the cardboard breaks down over time, it adds organic matter to the soil, enhancing its fertility and structure. I usually wet the cardboard before applying a layer of organic mulch on top to anchor it and provide aesthetic appeal.
Pick The Right Cardboard To Mulch
Not every type of cardboard is good for mulching, in fact, if you pick the wrong type of cardboard to mulch you might do more harm than good. Generally speaking, you should stick to simple cardboard, without any logos or writing on them, this is the safest cardboard that can be mulched. Make sure to stay away from cardboards that have some graphics designed on them, as these are not actually printed on the cardboard but on a thin layer of plastic.
The last thing you would want in your garden is cardboard mulch which has plastic, as the plastic will simply block the water from entering the soil, and eventually, it will dry it out. Make sure to also remove any duct tape from the cardboard as well, as the glue from the duct tape doesn’t mix well with the soil and the duct tape won’t actually decompose. If you are having problems with slugs and snails then check out my recent article How To Get Rid Of Slugs And Snails ( Top 19 Methods ).
Large Pieces Of Cardboard Or Shredded Cardboard For Mulching
Once you have some cardboard it is time to use it as mulch, but before that, you have to decide if you are going to use large pieces of cardboard or shredded cardboard. Larger pieces of cardboard will break down slower than shredded cardboard, although larger pieces tend to be excellent at smothering weeds out. If you have a larger garden then it is definitely easier to mulch with larger pieces of cardboard than with shredded ones, just use the ones that work the best for you. If you want to mulch with grass clippings then check out my recent article Grass Clippings As Mulch Pros And Cons ( Top 16 Pros and Cons ).
Place The Cardboard Mulch Around Your Plants
Make sure to place the cardboard mulch around your plants, in such a way that the mulch isn’t actually touching the stem of the plant. Cardboard is made out of wood pulp, which has a lot of nitrogen, which is beneficial for your plants but there is such a thing as getting way too much of something good. The excess nitrogen could burn the roots and the stem of your plants, so make sure that the cardboard is not in direct contact with your plants.
Layering The Cardboard Mulch
How thick or thin you should layer the cardboard mulch depends on what kind of cardboard you use. If you use large pieces of cardboard then one layer of these should be enough, some of them will most likely overlap but that shouldn’t be a big problem. If you are using large pieces of cardboard then do not stack the cardboard on top of each other in several layers as this will do more harm than good.
If you do this then the top layer will start to decompose as it will be able to absorb water, but the bottom layer will eventually dry out if doesn’t get enough water and you will notice that the soil above the mulch will start to deteriorate in a couple of months. If you are using shredded cardboard as mulch then a 2-5 inch layer should be enough, some people use a thicker layer which is also fine, but try to not layer it too thinly.
Water The Cardboard Mulch
Once you have layered your cardboard mulch it is time to water it. Watering the cardboard mulch has several benefits, as the cardboard absorbs water it will become heavier and wind will not simply blow it away. In addition to this, the excess water will start the decomposition process a lot faster. If you have a large garden then you might want to sprinkle the cardboard before laying it out, trust me it will be a lot easier to work with this way.
Adding Other Types Of Mulches On the Cardboard Mulch
Cardboard can be easily combined with other mulches, usually, people tend to do this for aesthetic purposes, because let’s face it if you only use cardboard mulch it looks like your plants are growing out of the cardboard. The most common mulches placed on top of the cardboard mulch layer are grass and wood chips, both work extremely well. If you are more concerned about how the mulch looks like in your garden then use wood chips.
If you are growing annual plants then you should add on top of the cardboard a type of mulch that breaks down relatively fast, like grass, hay, straw, and so on. Wood chips also break down but it takes a lot longer time for the nutrients from the wood chips to get into the ground.
Key Takeaways
- Cardboard can be an effective mulching material for suppressing weeds in your garden. When laid down properly, cardboard acts as a barrier that blocks sunlight, preventing weed growth and competition with your plants.
- Cardboard mulch helps retain moisture in the soil by reducing evaporation. It creates a protective layer that keeps the soil cooler and prevents water loss. Over time, cardboard breaks down and adds organic matter to the soil, improving its structure and fertility.
- Using cardboard as mulch is a convenient and budget-friendly option. It is readily available and often free, as you can reuse cardboard boxes or collect them from local businesses. It’s also easy to install, simply flatten the cardboard and place it on the soil around your plants, making sure to overlap the edges to prevent weed growth.
