If you buy potted plants or shrubs, they may well be root-bound. With nowhere else to grow, roots form tight circles inside the pot. As the plant grows, the tightly wound roots prevent water and nutrients from reaching the leaves. Before planting, gently coax these roots outward with your fingers. If the roots are very stubborn, make three or four vertical cuts in the root-ball with a sharp knife. Once planted, water often to help the plant get established.
To lighten large pots, fill the pot one-third to one-half full with foam packing peanuts. They not only make the pot lighter but also provide space for drainage. Fit a round piece of landscape fabric between the soil and the foam to keep the materials separate. You can use a light potting mix that contains plenty of vermiculite and peat moss to make the pot even lighter. Some packing peanuts dissolve in water; be sure to test yours before putting them in the pot.