With flowerpots, bigger is better. They do not dry out as fast and they hold more types of plants for larger root growth making for a dazzling display.
The pot must have a drainage hole, so the roots do not sit in water causing problems. Large plastic and glazed pots do not dry out as fast as clay ones because the water does not evaporate thru the sides. Plastic is lighter and can be moved easier, but they also allow the wind to tip them if not in a protected site.
Some fill the bottom of the pot with those Styrofoam peanuts and empty pop cans (good recycle idea) so less soil is used to save cost on potting soil. I like to fill the pot totally with soil for high root growth and leave in place.
Fill with a good potting soil like Miracle Gro to a couple of inches below the rim. Then moisten the potting soil before placing in plants so the plants do not float up. You can also use a mulch like a colored sphagnum moss or cocoa shells to help the soil from drying out too quickly.
Now decide if you want the pot to be in the sun or shade and select the plants accordingly. Use around 8 plants in a 20-inch planter and more for bigger pots. Do not plant too thickly because you want good airflow. Fertilize with a water-soluble fertilizer every other week.
