Using perennials in pots is another trend. Look for long-blooming perennials like Calamintha ‘Montrose White’. This low growing, well-behaved member of the mint family blooms for nearly two months and attracts butterflies. Each spring, I divide the Calamintha that grows in my perennial border and pop a few of the divisions into pots on the patio.

Ornamental grasses, like the native cultivar Panicum ‘Heavy Metal’,also look good in a summer container. Come fall, leave the grass but remove the petunias or other annuals and replace them with mums, tiny gourds and pumpkins. Changing some of the container plants takes the container well into autumn.

Smaller shrubs also can be used in large pots. Many of the compact panicle hydrangeas, like Hydrangea‘Little Lamb’have grown in pots around our patio during the summer. Come fall, I plant them in a permanent spot in my shrub border.

‘Apache Rose‘ switchgrass, Amsonia hubrichtiiand Hibiscus‘Cherry Cheesecake’are among the plants I like for long bloom, lasting form, good foliage or good fall color. Although it’s more perennial than shrub, Aralia cordata ‘Sun King’gets popped into a container in the shade garden because of its brilliant chartreuse foliage. It looks and grows like a shrub, and does well in dense shade to a half day of sun.

Choosing the Right Number of Plants

Use the diameter of the container to guide thevolumeof plants to buy. Divide the pot’s diameter by 2 to get the number of 4-inch plants you’ll need. For example, if the container is 14 inches wide, you’d need seven 4-inch potted plants.

Before removing the new plants from their pots, I position them in the container to see how they are going to look together. For perspective, focus on the area from the bottom of the container to the top of the vertical plant. A good ratio is for plant material to make up two-thirds of the total with the container as the remaining one-third. That ratio includes plants that cascade over the edge of the container.

Here’s another a simple design rule that bears repeating. Select one vertical plant, three cascading and three mounding filler plants to get the maximum impact.

Resources for Container Gardening

Check out the container gardening videosat PlantersPlace.com.

Some of my favorite books on container gardening.

Succulent Container Gardens: Design Eye-Catching Displays with 350 Easy-Care Plants by Debra Lee Baldwin.

Container Theme Gardens: 42 Combinations, Each Using 5 Perfectly Matched Plants by Nancy Ondra.