Ornamental · Apocynaceae
Annual Vinca
Catharanthus roseus
With heat, full sun, and free-draining soil, annual vinca carries a garden in color from late spring to frost.
Full sun
Every 5–10 days
50–95°F · 10–35°C
USDA 10–11
Overview
Annual vinca, the plant often labeled Madagascar periwinkle, is the quiet workhorse of the summer garden, the one that keeps a hot, sun-struck border looking composed when the heat has flattened everything around it. From late spring to frost it holds a steady wash of color, whites and pinks through to a deep blackberry-purple, set over glossy dark green foliage that reads as polished rather than fussy. For all its cottage-garden name, this is Catharanthus roseus, distinct from the trailing periwinkle that creeps along shady banks.
Its appeal lies in how little it demands of a busy household. Because it is heat and drought tolerant, it suits the gardener who waters on the way past rather than on a schedule, and it rewards a light touch far more than an attentive one. Overwatering is the one habit that undoes it, opening the door to the root and stem rots that are its single real vulnerability.
Placed with a little thought, it earns its keep season after season. Give it the hottest, brightest corner of the plot, soil that drains freely, and only the occasional drink, and it settles into the background of a garden as dependable summer color. It is the sort of plant that lets a space look effortless while asking almost nothing of the person tending it.
Care
The short version: choose the brightest, best-draining spot in the garden, and hold off planting until the season has properly warmed. Water deeply but only once the top of the soil has dried, keep the foliage dry, and feed with restraint.
Light
Reserve your sunniest position for annual vinca, since full sun brings the fullest, most colorful display, though it will accept a little partial shade. The brighter the spot, the denser and more richly colored the planting, while shade leaves it thin and muted.
Water
Water deeply but seldom, stepping in only when the week's rainfall slips below about an inch. Let the top half of the soil dry between waterings and keep the leaves dry, since a plant kept too wet at the roots or the foliage soon runs into disease.
Soil
Give it free-draining soil, a sandy or organic loam, and it will even settle into clay so long as water moves through freely. It looks its best in slightly acidic ground, a pH of 5.5 to 6.5.
Temperature
This is a plant for the warm months, at ease from 50°F to 95°F (10°C to 35°C) and most content at the upper end. Cold checks it and a damp chill invites rot, so it comes into its own through high summer, exactly when a garden needs the color most.
Humidity
Ordinary outdoor humidity is all it asks, with no reading to monitor. Air movement counts for more, since still, close air around a crowded planting is what allows leaf spot and gray mold to settle.
Feeding
A monthly feed through the growing season with a balanced general-purpose fertilizer is plenty, applied with a light hand. Overdo it and the reward is soft growth and a greater risk of root rot, not more flowers.
Pruning
There is no pruning to schedule here. The modern hybrids are self-cleaning, shedding their spent flowers on their own with no pinching or deadheading, which is part of what makes the planting look tidy with so little effort. The only task worth keeping up is removing declining leaves and blooms to hold disease at bay.
Size & spacing
Neat and low, the plants reach 6 to 18 inches (15 to 46 cm) tall and spread much the same, 8 to 18 inches (20 to 46 cm) across, which makes them easy to place at the front of a border or massed in a container. Set them with room for air to move between plants, and the planting stays healthy as well as handsome.
When to plant
Annual vinca keeps to the rhythm of summer, and it will not be rushed. Sow seed indoors in March in a warm spot, then wait to set the plants out until late May or early June, once frost has passed and the soil has warmed beyond 60°F (16°C). Plant into a cold, wet bed too soon and it stalls; give it the warmth it waits for and it carries color from late spring through to frost.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: March in warm temperatures
- Plant: Late May to early June, after frost and when soil temperatures exceed 60°F
- Harvest: Blooms from late spring or early summer (May to June) continuously until frost
Hardiness
USDA hardiness zones: 10–11
Temperature: down to -1°C
Troubleshooting
Nearly every setback with annual vinca comes down to water, whether pooling at the roots or lingering on the leaves. Saturated soil invites the rots from below, while splashed and standing moisture spreads the leaf spots and gray mold across the planting. Match the symptom below, then ease off the water and clear the affected growth before it takes hold.
Dark stem lesions before a sudden wilt and collapse
A planting that wilts and folds with dark stem lesions has almost certainly met Phytophthora stem blight and root rot, the disease that undoes more annual vinca than any other, brought on by wet soil and overhead watering. Lift a failing plant and the outer root tissue slides away from the core while the leaves yellow and scorch. Remove and bin the affected plants, work composted pine bark into the bed for drainage, and treat with potassium salts of phosphorous acid or a copper spray.
Fix:
- Remove and discard infected plants entirely
- Improve drainage by amending with composted pine bark
- Apply potassium salts of phosphorous acid as a soil drench or a copper-based spray
Yellowing and collapse while the soil stays moist
When a plant fails in soil that is still damp, the likely culprit is Rhizoctonia stem and root rot, which follows deep planting or frequent shallow watering. The roots tell the story, marked with brown lesions and stunting that rule moisture out. Lift the diseased plants with all their roots, then treat with thiophanate methyl or chlorothalonil as a spray or drench.
Fix:
- Remove diseased plants completely including all roots
- Use thiophanate methyl or chlorothalonil as a spray or drench
Banded, ringed spots climbing the lower foliage
Ringed, target-like marks moving up the foliage are the signature of Alternaria leaf spot, splashed onto the leaves by overhead watering. It opens on the lowest leaves as pinhead flecks, widens to about an eighth of an inch with its banded pattern, and works upward through the plant. Take out the badly marked plants, water at the base before dawn, and apply chlorothalonil weekly should it keep spreading.
Fix:
- Remove heavily infected plants
- Apply weekly chlorothalonil sprays for serious infections
- Clear dead plants after frost
Gray mold spreading over spent leaves and flowers
A soft gray coating over faded growth signals Botrytis blight, the gray mold that arrives in cool, damp spells among crowded plants. It settles first on the dead and dying tissue before moving on. Keep clearing declining leaves and flowers as they appear, and turn to a thiophanate methyl spray only when an outbreak becomes severe.
Fix:
- Remove declining leaves and flowers continuously
- Apply thiophanate methyl spray only if severe
Toxicity
For all its easy charm in a border, this is a plant to site with care. Every part holds vinca alkaloids such as vincristine and vinblastine, the compounds behind certain cancer drugs, and none of it is safe to eat. Ingested by a pet, animal, or child, it brings on drooling, vomiting, and diarrhea, with tremors, low blood pressure, and seizures possible after a large amount. Keep it well away from any household where curious mouths might reach it.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
A cat that chews any part usually begins with drooling, then vomiting and diarrhea, and often turns dull and withdrawn. A larger mouthful can lower the blood pressure and prompt tremors or seizures, so a call to the vet should not wait.
Dogs Toxic
A dog that samples the leaves or flowers soon drools, vomits, and develops diarrhea. Watch for a wobbly, low-spirited dog with low blood pressure, and treat any tremors or seizures as an emergency.
Horses Toxic
A grazing horse takes on an upset gut, loose manure, and a flat, sluggish mood from the alkaloids. Enough of it can bring muscle tremors and real weakness, so the plant belongs well clear of pasture and paddock.
Rabbits Toxic
The same alkaloids run through every part, so a rabbit that browses the foliage can expect drooling, diarrhea, and a slumped, low-energy posture. It is no plant to leave within reach of a hutch or a roaming rabbit.
Livestock Toxic
Cattle, goats, and sheep that graze annual vinca take in vinca alkaloids that upset the stomach and drain their strength. Heavier feeding can bring staggering and tremors, so it should be fenced off from grazing animals.
Birds Toxic
Birds are not exempt, since the alkaloids sit in leaves, stems, and flowers alike. Even a few pecked petals can prompt vomiting and weakness, so keep the plant clear of aviaries and away from poultry.
People Caution
No part of annual vinca belongs on a plate. Eating the leaves or flowers can bring drooling, nausea, vomiting, and diarrhea, with tremors or low blood pressure after a large amount, so keep it out of reach of inquisitive children and pets.
Keep away from pets; all parts contain alkaloids. Typical exposure causes GI upset, with neurologic signs possible at higher doses.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Plant breeders have refined annual vinca over the years, chasing better disease resistance and fuller, more striking flowers. These are the series most likely to turn up at the garden center.
Cora Group (Cora XDR)
Choose this series for a bed with a history of rot, since breeding gave it resistance to several strains of Phytophthora, the root and aerial diseases that most afflict this plant.
Pacifica Group
A compact, bushy bedding series that offers generous blooms across a broad palette of colors.
Titan Group
A mounding series whose oversized flowers keep their poise right through the fiercest summer heat.
Jams 'N Jellies Blackberry
Grown for the drama of its dark flowers, a deep blackberry-purple lifted by a clean white eye.
How to propagate
Annual vinca is raised from seed, and the whole exercise hinges on warmth. Start it early indoors, and resist the temptation to move it outside before the season has genuinely turned.
SeedModerate
Sow indoors in March in warm conditions; transplant outdoors in late May to early June after frost · Several weeks to germinate and establish before transplanting outdoors
Annual vinca is grown from seed, and the single requirement is warmth. Sow indoors in March and keep the tray genuinely warm, since cool seed simply refuses to stir. Allow the seedlings their several weeks to germinate and fill out, then keep them under cover until late May or early June, once frost has passed and the soil has climbed above 60°F (16°C).
Myths
Annual vinca is simply the trailing groundcover periwinkle under another name.
In fact they are two separate plants that share nothing but a family. Annual vinca is Catharanthus roseus, an upright to mounding warm-season bedding flower, while the trailing perennial groundcovers are Vinca minor and Vinca major in a genus of their own. Both belong to Apocynaceae, and the resemblance goes no deeper than that.
Annual vinca needs constant watering and deadheading to keep flowering.
The truth runs the other way. Being heat and drought tolerant, it flowers without pause from late spring to frost and asks for no deadheading at all. Lavish extra water on it and the return is not more bloom but the root and stem rots that are its one real weakness.