Dahlias (Dahlia spp.) make up a large group of plants that grow from tubers and come in many sizes, with flowers in an array of shapes and many different colors. One type of feather-petaled dahlia (Dahlia pinnata), called a dahlietta, is an especially petite, upright, bushy plant. It can survive year round in warmer regions within U.S. Department of Agriculture plant hardiness zones 9a through 11b, but is usually grown as an annual. With a bit of end-of-season care, you can also save dahlietta tubers to grow again the following spring.
Dahliettas are shorter than most other dahlia varieties. For example, the cultivar 'Sunburst' is about 8 to 12 inches tall and 12 inches wide, with bicolor flowers composed of large red petals surrounding smaller, inner yellow ones. Other dahlietta cultivars that are of equivalent size include 'Apricot Sunrise,' 'Violet Frost' and 'Cherry Sunrise.'
Although you can start these dahlias from seed, to have flowers the first season it's best to start with bareroot tubers or with potted plants that are already growing, both available at nurseries and garden centers.
Set tubers or plants in a spot that gets full sun, spacing them about 8 inches apart and keeping the crown of each plant just above the soil level. They also tolerate partial shade but may produce fewer flowers under these conditions. You can also plant dahliettas in outdoor pots, with about two plants in a 10- or 12-inch pot.
Never pot dahlias in garden soil, which can harbor insects or their eggs. Instead, use commercial potting soil.
Keep the plant's soil evenly moist, providing extra water whenever the top inch of soil is dry to the touch. Avoid wetting a dahlietta's leaves by using a soaker hose or drip irrigation; this helps prevent fungal problems. When the plant has started to show new growth, carefully mix a small handful -- about 1/4 cup -- of a granular 5-10-10 formula into a circular furrow around each plant, taking care not to disturb the roots. Water the fertilizer in well and repeat the treatment in mid-summer.
Although dahliettas can be grown as annuals, discarding plants at season's end, you can also save the tubers for the next year by gently lifting the plant with a garden fork in the fall after your first frost or by the end of October if frost is rare where you live.
Digging up the plant is advisable even in warm-winter areas within the plant's growing range, to prevent rotting of the tubers during winter.
Once out of the ground, cut off the upper part of the plant with shears, leaving about 3 or 4 inches of stem attached to the tubers; wipe your blades with rubbing alcohol between each cut to prevent spreading plant diseases.
Remove loose soil from the lifted tubers, taking care not to damage them, and set them indoors at room temperature, turning the tubers upside down so any liquid in the stems can drain. Once remaining soil has dried, brush it off and discard any damaged or soft tubers. Place the remaining tubers in a cardboard box or a basket with some peat moss or sawdust in the bottom, then cover them with the same material, but leave the stem ends exposed to air. Store the box or basket in a dry, cool spot that won't freeze -- a basement or unheated room -- until spring when frost danger has passed and you can replant them outdoors.