QUESTION: Should I put cardboard in raised beds? I don’t want to use that plastic weed barrier stuff. – Hannah G.
ANSWER: Cardboard is a great resource to use in raised beds, especially when you are trying to save money on supplies. Cardboard can be purchased very cheaply from moving supply stores or big warehouse style businesses like Wal-Mart or Home Depot. However, nine times out of ten, if you need cardboard and you are resourceful, you can get all the cardboard you need for free, either from friends who recently moved, or from grocery stores or smaller stores who have excess cardboard that they don’t have any use for.
The best type of cardboard to use for a raised bed liner is the kind that is thicker, with corrugated layers, instead of the thinner, more flimsy kind. You should also look for the standard, brown-colored cardboard with little to no printing on it and avoid using any cardboard that is dyed a different color, or covered in print, especially the kind printed with glossy ink, as the dyes and inks that are used to color the cardboard will leach out into the soil when the cardboard gets wet or starts to break down. Toxins released by dyes and inks can have harmful effects on the soil in your garden beds and can potentially hurt the plants you grow in your raised beds as well.
The corrugated cardboard that is typically used for larger boxes is recommended for lining your raised beds, as it takes much longer to break down and decompose than thinner, flimsier cardboard types. Because cardboard, and other paper products are made out of cellulose, it will enrich the soil as it decomposes and breaks down into the soil itself.
Many people use newspapers instead of cardboard to line their raised beds. Though newspaper is also made out of cellulose, it is inferior to cardboard for raised bed lining for several reasons. One, newspaper is typically covered in ink, which can add toxins to the soil as it breaks down. Two, newspapers, even if you use a nice thick stack of them, are thinner, and much less sturdy than multi-layered, corrugated cardboard, which means they will break down much quicker than the cardboard would. If you are lining the bottom of your beds in an attempt to keep pesky weeds from growing up from the bottom of your raised beds, cardboard should serve as a better, and longer-lasting deterrent.
For people who are making raised beds who are not on a strict budget, landscape fabric can be used instead of cardboard for lining the bottom of raised beds. Landscape fabric is more durable than cardboard, and will take a much longer time to decompose, so it won’t have to be replaced as often, and will keep weeds at bay in the same way cardboard does, but with a longer lifespan. Landscape fabric is a great choice for raised bed liners, as it is permeable, long-lasting, and has excellent drainage.
Burlap fabric is also a common choice for raised bed lining. Burlap is environmentally friendly, it’s cheaper than landscape fabric, and it is also slow to decompose. However, landscape fabric is preferred, as burlap is prone to fraying, and will break down quicker than landscape fabric. Both of these options are quite costly though, especially if you are lining many raised beds, or your raised beds are very large. Cardboard or newspaper liner are much cheaper options that basically do the same thing, as long as you don’t mind replacing them every one and a half to two years.
Using cardboard as a liner for the bottom of your raised beds to deter weeds from growing up is just one of many garden uses for cardboard. If you are having a serious problem with weeds in your garden beds, you can lay down a layer of cardboard over the top of your beds at the end of the growing season. Then cover the cardboard layer with soil and mulch, and keep the cardboard in place until you are ready to prep your beds for the next planting season. When you remove the cardboard, you should have a much easier time with weeds in the following season.
You can even use a top layer of cardboard during the growing season to keep weed problems down to a minimum. Simply lay out the cardboard on the top layer and cut holes into the surface which are large enough to plant your seeds or seedlings into, allowing enough room for the stems of the plants to comfortably expand. Then add a layer of soil (optional) and a bit of mulch, pine needles, or wood chips over the cardboard just to cover it up so that your garden looks nicer.
If you grow squash or zucchini in your garden, another way to put excess cardboard to use is to reuse your cardboard toilet paper and paper towel rolls as a protective barrier around the base of the plant’s stem to prevent squash vine borers from entering your plants and wreaking havoc on your squash crops. Simply cut a vertical line down the length of your toilet paper rolls so that you can easily open it up to fit it around the base of your plants. You can position your protective cardboard rolls around the base of your squash plants when they are 4-6 inches or taller.
If you are planning to install walkways around your raised beds made from wood chips, gravel, rocks, or a mulch of some kind, you can also prevent weeds from growing up in your walkways by laying down a layer of cardboard at the bottom of the walkways before adding the loose gravel, wood chips, or mulch over the top. Of course, this won’t be a permanent weed deterrent, as both cardboard and wood chips eventually break down, which will allow weeds to grow up into your walkways eventually. However, using gravel or rocks, or occasionally replacing the wood chips or mulch in your walkways will prevent weeds from overtaking them.
Cardboard boxes with the top and bottom taken off can also be placed around plants during the cold seasons to extend the harvest time for a few weeks and protect the plants from cold weather and winds. In this way, cardboard boxes can be repurposed as cold frames to protect your plants from bad weather and extend the growing season.