Question
our comunity is building 4 planters to go on main street that are 4ft X 4ft and 2 ft deep with a raised inner square 2ft x 2ft. would like to put 6 in. of styrafoam chips in the bottom for air as well as drainage and to reduce the weight. Has anyone ever tried anything like this? Any suggestions as to soil content or plants. This is in Alberta's dry belt. gets very HOT as a rule.
am considering portculaca, lobelia, sunflowers,hanging carnations,trailing alyssum, asarina victoria falls,fuchsia swing,daisys nothing too fragile for the first year.

Answer
Yes I have heard of putting styrafoam chips and many other materials in the bottom of containers. I personally don't recogmmend it. The main reason is that, it is dead space, with no soil that the roots can use. Some of the plants will send roots to the bottom of the container to reach moisture. If you add material to the container it makes the soil shallow and that means shallow roots. While the container will be heavy to carry, the weight will make it less top heavy, less likely to tip over.
Get the best potting soil you can afford. If you can find one with fertilizer and moisture retaining polymers, that is even better. If not, then add the slow release, fertilizer and polymers to the bottom two thirds of the soil in the container. Mix in well. This will mean you will need to feed and water the flowers less all summer. Saves work.
Looking at your list of plants, I would use yellow Marigolds in place of the others  They will bloom all summer, (which the things on your list may not do,) and they are tough as nails and heat tolerant.They need to be dead headed often to keep them looking good. This can be done by hand a few minutes every week. Some purple million bells and some white bacopa falling over the sides will be nice as well. For a contrasting silver amoung the mass of yellow, put a few dusty miller. So you would have a color design of yellow, purple, white, and silver for a whole season.

bakerplanter