In this way, what do I fill the base of my planter with?
If you have an especially big planter to fill, light, bulky materials are your best bet. Examples include plastic drink containers, milk jugs, crushed soda cans, foam packing materials and plastic or foam take-out containers.
Secondly, do I need to put rocks in the bottom of a planter?
This is false. Putting gravel, rocks, or other layers of material in your plant pots, planters, or containers with drainage holes does NOT improve potting soil drainage, it instead increases the water saturation level that leads to root rot.
Should I put gravel in the bottom of my planter?
A: For years, experts told gardeners to put a layer of gravel, pebbles, sand or broken pieces of pot in the bottom of the pot before potting up houseplants or outdoor plants. The idea was to improve drainage. But research shows that this advice is wrong. Water doesn’t travel well from one medium to another.
Line the entire planter with a sheet of plastic, trimming it so that it reaches but does not go over the rim. Staple the plastic all the way around the rim. Using a screwdriver or sharp stick, poke through the drilled drainage holes to let excess water drain out of the plastic liner.
You can use packing peanuts as long as they’re not the type that dissolves in water. Styrofoam peanuts do an excellent job. Make sure they’re secured within a bag to keep them stable and in place. It also makes your life easier if you decide to repot the plant.