The popular evergreen groundcover Vinca, or periwinkle, is often sought for its year-round color. Whether it survives winter depends on its specific species and the regional climate. Understanding its cold tolerance, measured by the USDA Hardiness Zone system, is the first step in ensuring its survival and applying appropriate cold-weather protection.
Distinguishing Vinca Species and Cold Tolerance
Winter survival is largely decided by identifying the two most common species of periwinkle. Vinca minor, often called lesser or dwarf periwinkle, is the hardier species, reliably surviving in USDA Hardiness Zones 4 through 9. This means V. minor can withstand average minimum winter temperatures as low as -30°F to -20°F.
Vinca major, known as greater or bigleaf periwinkle, is much less cold-tolerant, generally performing as a perennial only in Zones 7 through 9. In areas colder than Zone 7, V. major may suffer significant dieback and is sometimes treated as an annual. The difference in inherent cold resistance between these two species determines if a Vinca planting will return in the spring.
How Vinca Survives the Cold Season
Periwinkle survives the cold by entering semi-dormancy, slowing its metabolic processes. As an evergreen, the foliage remains throughout the winter, but growth halts when temperatures drop significantly. This reduced activity conserves energy reserves stored in the root system.
The dense, low-growing foliage provides insulation to the soil beneath the plant. This evergreen layer helps moderate soil temperature fluctuations, protecting the crown and shallow root structure from rapid freezing and thawing cycles. Even if above-ground leaves suffer damage, the protected roots hold the energy necessary for new growth in spring.
Practical Steps for Winterizing Vinca
Preparing Vinca for winter increases its chances of survival, especially in the colder limits of its hardiness zone. First, ensure the ground is sufficiently watered before the first hard freeze. Since Vinca is evergreen, its leaves continue to lose moisture through transpiration even when the ground is frozen, making pre-winter hydration necessary to prevent desiccation.
Apply a layer of organic mulch, such as shredded leaves or straw, to protect the roots from severe cold. This protective layer should be applied after the ground has frozen solid. This keeps the soil temperature consistently cold and reduces the risk of frost heave, which occurs when repeated freezing and thawing cycles push shallowly rooted plants out of the soil, exposing their crowns and roots.
Planting location also offers winter protection by taking advantage of microclimates. Sites near a building foundation or under the canopy of large evergreen trees are often warmer and sheltered from harsh winter winds and direct sun scald. These spots provide natural buffers that can make the difference between survival and winter injury, especially for V. major or V. minor planted in Zones 4 and 5.
Assessing and Recovering from Winter Injury
In early spring, look for signs of winter injury, which often manifest as brown, scorched, or brittle leaves on the evergreen stems. This discoloration is usually a result of desiccation from winter wind or sun combined with frozen ground, preventing the roots from replacing lost moisture. Damaged foliage does not mean the entire plant has died.
The most effective recovery strategy is to prune back the damaged material to encourage new growth from the roots. Use sharp shears to cut back dead or discolored stems to the ground level or back to healthy green tissue. Once new shoots emerge, applying a light, balanced fertilizer can help Vinca quickly fill in bare patches.