Materials needed for this step: Liner and Cutting Utensils.
In this step, we want to prep and insert the liner. This piece is one of the most important because it holds in the interior of the planter and controls flooding.
For this step to be completed smoothly, a large amount of table space is recommended. Lay out the liner flat onto the work surface. My liner will be used to fill two enclosures, so the plastic shower liner needs to be cut into two pieces large enough to cover the interior of each planter.
Simply lay out the liner and cut the plastic roughly into the needed size. For this step, it is better for the liner to be cut into oversized segments and trimmed after it has been properly fitted and filled. For this reason, do not worry about making cutting the pieces too big. The liner needs to be placed into the planter and spread out so it hugs the outer walls and takes the shape as a planter. Now trim the liner and repeat using the leftovers to line the second planter.
Carefully take out the liner while trying to retain its shape in the planter. Now cut a small slit into the liner about an inch long a few inches from where the bottom of the planter is. Try not to cut the slit too high if the planter is shallow. Cut no more than three slits throughout the liner at this height. For my liner, I am cutting at two points. One on the right and the other on the left side.
Very carefully, reinsert the liner. Once it is in place feel around to make sure the slits are located in the correct position. Play around with the liner until it is in the perfect spot.
Now there is a place for excess water to drain incase the plants are over watered. This also gives the roots ventilation and helps prevent root rot.