A large planter makes a bold statement in front of a home or on a porch. Fill its wide mouth with a number of different flowers to create a living bouquet. Unlike smaller planters, you should not fill large planters with soil. It will make the planter heavy to move inside and outside as the weather changes. And, the plants don't need all that soil. Substitute some of the volume with lightweight material and your plants will grow just as happily as in any other container.
Approximate the adult height of the largest plant that will grow in your planter. Add 2 to 3 inches. When in doubt, 1 foot of soil is usually sufficient.
Fill the bottom of the planter with polystyrene packing peanuts. Allow enough space in the top of the planter to accommodate the depth you calculated in Step 1.
Spread two to three sheets of newspaper over the top of the packing peanuts to prevent the planting mix from falling through.
Fill the top of the planter with lightweight planting mix to within 1/2 inch of the lip of the planter.