This will force air out of the pore spaces and help keep the soil moist. Consider putting casters on wooden planters or putting your large pots on a little dolly before they're filled with soil. A 30-gallon planter can weigh more than 200 pounds. Head off unnecessary heavy lifting by filling and planting containers at the site of their final destination. Potting soil can be used two or three years, unless plants become diseased.
Results are best if the soil is changed every year, however.
Some plants can survive on only 4 hours of sun per day. But most plants, especially annuals, require at least 6 to 8 hours per day. Perennials can be dandy container plants. However, you'll likely have to remove them from the containers in the fall and replant in the permanent landscape. Let us hear from you.