I have used old compost bags for years (black side out) They are strong and FREE. I do not start my drainage holes at the bottom though , but a couple of inches up as I think it helps to retain water better. Also, it's best to put a larger than required piece of the bag in the container, fill it with the compost and plants and then water. The weight of the water pushes the bag into the container. Trim the bag AFTER this and you wont find that later waterings come pouring over the top of the liner because you cut it to short in the first place (The voice of experience here see!!) Sanjo