There are several liners available out there, such as the Joen 36 Inch Extra Thicker Trough Coco Liner. You can also use landscape fabric as a liner. Some of these products cost as much as or more than the price of your planter boxes if you're going for the more affordable ones. It's natural that people would ask if it's worth buying a liner, or if it's something that they can forego. There are quite a few benefits that you can get out of using a planter box liner. It provides your planter box with good drainage as it can keep your soil moist but doesn't allow water to stagnate. It also helps with too much soil loss because it keeps the soil from getting washed away while water drains out. This means that you have less mess around your planter boxes. Liners can also keep soil from getting in contact with your planter box. If you're planting on a raised bed, these liners help keep the weeds and pests out. However, there are some cons. For instance, using a plastic liner might mean that your soil is not getting enough drainage. Liners are also a pain to replace. Most of the time, you will need to remove everything from your planter box, replace the liner, and put everything back.