Container Gardening: Don't Waste Money on All That Soil! Try This Hack Instead by Jan Mostrom
I love spring and summer and the beautiful flowers that are everywhere. I especially love having lots of containers in and around my home. Some of my containers are very larger, so I got this tip from my good friend, Chris, to lessen the amount of potting soil I need to use.
When you have a large pot, use a "filler" in the bottom half to take up space. I like to use empty plastic water bottles or packing pellets tied up in a plastic bag. Put them in the bottom of the container, and then pour your soil over it and you'll use 33 to 50 percent less! In the fall I just scoop out most of the soil and leave the packing material inside the containers to reuse next year. I've never had to replace the filler in over 10 years and it doesn't harm the roots or the flowers.