Vinca (annual vinca, Madagascar periwinkle)

About Vinca (annual vinca, Madagascar periwinkle)

Annual vinca is a tough summer bedding plant with glossy leaves and flat, five-petaled flowers that keep coming through the hottest, driest weather. It wants full sun, warm soil and good drainage; wet, cool soil brings on root and stem rots, so the disease-resistant Cora and Nirvana series are worth seeking out (Clemson, LSU). It is not the same plant as the groundcover periwinkles Vinca minor and Vinca major, which spread aggressively and are on many states' invasive lists (NC State).

Grown as a warm-season annual in every zone; it lives through winter only in zones 10-11 (NC State, UF/IFAS). UF/IFAS rates it 'caution - manage to prevent escape' in South Florida (advisory), and it can reseed.

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

Plant only after the ground is warm, above 60 F, usually May in South Carolina; early planting invites root rot (Clemson). Seed sprouts in about a week at 70-75 F in the dark (UF/IFAS), but plants are slow to flower from seed, so most people buy transplants; no days-to-bloom count is sourced. Set the root ball level with or a bit above the soil, 8-18 inches apart, and don't replant vinca in the same bed year after year (LSU, UF/IFAS). Most gardeners replant each spring; we found no extension advice on bringing it indoors for winter.

Soil

Well-drained soil with some organic matter such as composted pine bark; best at pH 5.5-6.0, since high pH makes disease worse. Raise beds if drainage is poor (Clemson, LSU).

Dig the whole bed and work in organic matter such as composted pine bark for drainage; aim for pH 5.5-6.0 and add lime only if a soil test calls for it (Clemson).

Feeding

• Only if a soil test shows a need: fertilizer chosen by soil test, avoiding ammonium-type nitrogen. Fertilize by soil test results and skip high-ammonium fertilizers such as ammonium nitrate or ammonium sulfate (Clemson).

Too much fertilizer and frequent watering both bring on disease; water only when rain gives less than about an inch a week, and plant only after the soil is above 60 F (Clemson).

Harvest

Blooms from May or June until frost. Vinca needs no deadheading or pinching (Clemson, NC State); remove plants after a hard frost to cut down on diseases next year.

Varieties (14)

Extension sources document 14 annual vinca series; groundcover periwinkles (Vinca minor, V. major) are different plants and not listed.

Pests to watch for

Thrips

Diseases and problems

Phytophthora aerial blight and root rot, Pythium root rot, Rhizoctonia stem and root rot, Alternaria leaf spot, Gray mold, Tomato spotted wilt

In the kitchen

Safety: All parts contain vinca alkaloids; NC State rates it low severity, but eating large amounts can cause vomiting, low blood pressure, hallucinations, seizures and worse. Don't eat any part. Its compounds led to important leukemia drugs, which is no reason to use the plant itself.

Pets: Toxic to dogs, cats and horses (ASPCA, listed as periwinkle, Vinca rosea): vinca alkaloids can cause vomiting, diarrhea, low blood pressure, depression, tremors, seizures, coma and death.