Carnations (Dianthus spp.) are perennial plants that thrive in temperate climates but can struggle in extreme cold. Their hardiness varies by species, with some tolerating temperatures as low as -20°F (-29°C), while others are less resilient. To overwinter carnations successfully, it's crucial to know your specific variety's cold tolerance. For example, Dianthus caryophyllus (common carnation) is less cold-hardy than Dianthus gratianopolitanus (alpine varieties).
As temperatures drop, carnations enter dormancy. To prepare them for winter:
a. Stop Fertilizing: Cease fertilization by late summer to avoid stimulating new growth that won't harden before frost.
b. Reduce Watering: Gradually decrease watering in fall to help plants acclimate. Overly moist soil in winter can lead to root rot.
c. Trim Spent Blooms: Lightly prune dead flowers and weak stems, but avoid heavy pruning, as foliage helps protect the crown.
Carnations are vulnerable to freezing temperatures, especially in zones below USDA Zone 5. Key protection methods include:
a. Mulching: Apply a 3–4 inch layer of straw, pine needles, or shredded leaves around the base after the first hard frost. This insulates roots and prevents freeze-thaw cycles.
b. Covering Plants: Use frost cloths or burlap to shield plants during extreme cold snaps. Avoid plastic, which traps moisture and causes rot.
c. Container Plants: Move potted carnations indoors to a cool (40–50°F/4–10°C), bright location, such as a garage or sunroom.
Potted carnations require special attention:
a. Insulate Pots: Wrap containers with bubble wrap or burlap to prevent root freezing.
b. Reduce Watering: Water sparingly—just enough to keep soil slightly moist. Overwatering in dormancy is fatal.
c. Monitor Light: Ensure they receive indirect sunlight if kept indoors to prevent etiolation (weak, leggy growth).
Carnations face several risks during cold months:
a. Crown Rot: Caused by excess moisture. Ensure well-draining soil and avoid mulch touching stems directly.
b. Rodent Damage: Mice and voles may nest in mulch. Use wire mesh or repellents if needed.
c. Snow Load: Heavy snow can break stems. Gently brush off accumulations or use supports.
As winter ends, gradually reintroduce carnations to outdoor conditions:
a. Remove Mulch Slowly: Clear mulch once frost risk passes to prevent mold and allow new growth.
b. Resume Watering: Increase hydration as temperatures rise, but avoid waterlogging.
c. Prune Damaged Growth: Trim any winter-killed stems to encourage healthy regrowth.
