Annual
Annual Vinca / Madagascar Periwinkle
Catharanthus roseus · Apocynaceae
Also called: Vinca, Periwinkle, Rose periwinkle, Cape periwinkle
Annual Vinca / Madagascar Periwinkle (Catharanthus roseus) is a low-water annual well suited to Tucson and the low desert. It thrives in full sun, with a moderate to fast growth rate.
Annual Vinca / Madagascar Periwinkle at a glance
- Water use
- Low (established)
- Sun
- Full sun; the toughest summer annual for reflected heat and western/southern exposures. Tolerates light afternoon shade but blooms best in full sun.
- Mature size
- 8-18 in tall and wide depending on variety (trailing 'Cora' and 'Cascade' types spread wider)
- Growth rate
- Moderate to fast
- Bloom
- White, pink, rose, red, lavender, and purple, many with a contrasting eye, Late spring through the first frost (roughly May to October/November); one of the few annuals that blooms reliably right through Tucson's brutal summer.
- Cold hardiness
- Frost-tender; killed by the first hard frost. Heat-loving, thrives at 100F+. Do not plant until soil and nights are warm.
- Soil
- Well-drained soil is essential; amend Tucson's caliche/clay with compost and ensure good drainage. Tolerates alkaline pH.
- Native range
- Madagascar (widely naturalized in tropics); grown as a warm-season annual in Tucson
- Best used as
- Summer color beds, Borders, Mass plantings, Containers and hanging baskets, Reflected-heat and western-exposure spots
- Wildlife
- Attracts some butterflies; not a major pollinator magnet. Generally not browsed by rabbits or javelina due to toxicity.
- Toxicity
- Toxic to dogs, cats, and horses (ASPCA) and to humans. All parts contain vinca alkaloids (e.g., vincristine, vinblastine); ingestion can cause vomiting, diarrhea, low blood pressure, tremors, and seizures. Keep away from pets and children.
How to grow Annual Vinca / Madagascar Periwinkle in Tucson & the low desert
Watering
Plant in late spring after soil warms (mid-April through May/June). Water deeply 2-3 times per week in summer once established; let the top inch dry between waterings. Overwatering and cool wet soil cause root and stem rot (Phytophthora/Rhizoctonia) - the single most common failure in Tucson, so avoid planting early in cool soil.
Fertilizer & nutrients
Light feeder. Work compost into beds at planting and apply a balanced slow-release fertilizer; supplement monthly with a dilute liquid bloom fertilizer (e.g., 10-10-10 or a blossom-booster) through the growing season. Avoid overfeeding nitrogen, which gives leaves at the expense of flowers.
Pruning & care
Self-cleaning - no deadheading required. Pinch young plants once to encourage branching; shear lightly if plants get leggy in late summer.
Notes
Do NOT confuse with trailing Vinca major/minor (a separate genus). The #1 mistake in Tucson is planting too early into cool, wet soil, which causes fatal stem rot - wait until consistently warm weather. Best heat performer of all summer annuals here. Reseeds modestly.
Sources: University of Arizona Cooperative Extension - Pima County Monthly Gardening Guides (April/May); ASPCA Toxic and Non-Toxic Plants: Vinca; Growing in the Garden - Arizona Annual Flowers Low-Desert Guide