There are two ways to make your garden beautiful year around: one is to choose plants that have some interest in any season (colorful flowers in the summer, pretty fruit or berries in the fall and lovely red leaves in the winter), or to choose plants that you like, even if they are not suitable for your climate, grow them in the garden during hot months, and then move them indoors.
Japanese or red maples are true kings of any garden. The leaves keep changing color from the pale green in the spring to the fiery red in the fall, staying on the tree long into the winter. A garden with a maple requires a comfortable but sturdy bench to be enjoyed for hours. Crab apple has it all: fragrant flowers, lovely red fruit, and interesting mottled bark. Magnolia can make even the most boring front yard into a showpiece. Hydrangeas will explode into pink or blue flowers in the spring, to slowly change color as they age.
If you like flowering plants that are not hardy in your zone and do not have a greenhouse, you might want to use your sunroom as a conservatory and place your favorite bushes and flowers inside. Make sure that the sunroom is insulated. Camellias, azaleas, oleanders and many other favorites can easily be potted and placed indoors for the winter. If the weather turns really cold, you might have to heat your sunroom for a few days. With a nice patio set, you can continue to enjoy the bloom and fragrance of your lovely garden long into the winter.