Fundamental Facts
HARDINESS: Tender
PREFERRED SOIL pH: Neutral
PREFERRED SOIL TYPE: Average
PREFERRED LIGHT: Sun to partial shade
ATTRIBUTES: Compact plants; blue, pink, red, purple, white flowers; for beds or pots
SEASON OF INTEREST: Summer to fall
FAVORITES: 'Cooler' and 'Pacifica' for a range of colors
QUIRKS: Grows poorly in cool, damp conditions
GOOD NEIGHBORS: Ageratum, buddleia, marigold, salvia, zinnia
WHERE IT GROWS BEST: Full sun in warm, well-drained soil
POTENTIAL PROBLEMS: Root rot in cold, wet soil
CRITTER RESISTANCE: Excellent
SOURCE: Bedding plants
DIMENSIONS: 6-18 in (15.2-20.2 cm) fall, 8-12 in (20.3-30.5 cm) wide
Periwinkle in the Landscape
In the heat of July and August when many garden plants are taking a siesta, periwinkle is at its best, soaking up the most blistering weather of the season. This easy-care performer loves high temperatures and thrives equally in the dry heat of a Southwest summer or the sticky atmosphere of the southeastern coastal areas.
Often called annual vinca, this flower also goes by the name of Madagascar periwinkle. Shiny dark green leaves frame flat, 2 in (5.1 cm) wide flowers that often show a contrasting white or red central eye. The highly uniform plants grow 12-15 in (30.5-38 m) high and wide, making them ideal for edging and mass planting. Depending on variety, flower colors may be neon pink, soft lilac, or white with pale yellow centers, and virtually any shade in between. The flowers are not only colorful but also self-cleaning, which means that they drop from the plant as they fade.
Choosing a Periwinkle
Because vinca is such an excellent annual for the hottest part of the season, it's not surprising that soft pink and lilac-colored plants are valued for their icy cool hues. Popular series including 'Cooler' and 'Paciflea' offer these shades along with much brighter ones. If you want to attract plenty of attention from a distance, choose deep pink 'Stardust Orchid', which is marked with a star-shaped white eye, or the dark, rose-pink variety 'Pacifica Punch'.
Some periwinkles are bred to be more compact than others, but the height a variety attains depends more on the length of the growing season than its genes. In the North, periwinkle rarely grows taller than 8 in (20.3 cm), but in warmer climates gardeners can expect it to grow to 18 in (45.7 cm) tall or even taller. Plants often reseed, too, although seedlings do not appear until late spring, after the soil has warmed.
Growing periwinkle
Periwinkle is not difficult to start from seed, but you will save time and trouble by buying bedding plants. Wait until the soil is warm to set out seedlings, or use them as early summer replacements for cool-season annuals. Amend poor soil with a balanced organic or controlled-release fertilizer at the rate recommended on the label, but do not over-fertilize this flower. In fact, it is more important to provide a well-drained spot and soil that is warm enough to promote fast growth. Plants grown in cold, clammy soil may develop problems with root rot, which causes them to suddenly collapse and die. In cool climates, it's best to grow periwinkles in dark-colored, sun-absorbing pots until summer weather becomes suitably warm, then set them in the ground.
Periwinkles need no grooming or trimming, though they often benefit from a booster feeding of a balanced fertilizer, such as 10-10-10 sprinkled over the root zones of the plants in midsummer. Also, do not plant periwinkle in the same place more than once every 4 years. The roots host a potentially deadly fungus, which can become a serious problem if the growing site is not routed properly.
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