Ornamental · Apocynaceae
Annual Vinca
Catharanthus roseus
Give it heat, sun, and dry-side soil, and annual vinca blooms from late spring straight through to frost.
Full sun
Every 5–10 days
50–95°F · 10–35°C
USDA 10–11
Overview
Annual vinca, better known as Madagascar periwinkle, is the bedding plant for the spots that defeat everything else: hot, sunny, and bone dry by midsummer. It flowers without pause from late spring until frost, in shades that run from white through pink to a deep blackberry-purple, each bloom set against glossy dark green leaves. Despite the common name, it is Catharanthus roseus, not one of the trailing periwinkles people often confuse it with.
What makes it easy is also what trips people up. It is heat and drought tolerant to a fault, so the real risk is kindness in the form of too much water. Soggy ground invites the root and stem rots that are this plant's one serious weakness, and once they take hold there's no saving the plant.
Treat it as a warm-season annual and the rest falls into place. Wait for genuine summer heat before planting, give it full sun and soil that drains fast, then water only when it truly needs it. Do that and you get months of color from a plant that asks for almost nothing in return.
Care
The short version: full sun, fast-draining soil, and real summer warmth before you plant. Water deeply but only when the top of the soil has dried, keep the leaves dry, and go easy on the fertilizer.
Light
Give annual vinca full sun for the best flowering, though it will take a little partial shade. The more direct light it gets, the denser the plant and the heavier the bloom, while shade thins it out and dampens the color.
Water
Water deeply but rarely, only stepping in when weekly rainfall drops under about an inch. Let the top half of the soil dry between drinks, and keep the spray off the foliage, because wet leaves and soggy roots are what invite disease.
Soil
Plant in well-drained soil, whether that's a sandy or organic loam, and it will even cope with clay so long as the water runs through. Aim for a slightly acidic pH of 5.5 to 6.5, which is where it grows best.
Temperature
This is a heat lover, comfortable from 50°F to 95°F (10°C to 35°C) and happiest at the warm end of that range. Cold checks its growth and damp chill invites rot, so it earns its keep through the hottest part of summer.
Humidity
Average outdoor humidity suits it fine, with no number worth chasing. Air movement matters more than the reading, since still, muggy air around crowded plants is what lets leaf spot and gray mold settle in.
Feeding
Feed monthly through the growing season with a balanced general-purpose fertilizer, and apply it sparingly. Pile on too much and you don't get more flowers, you get soft growth and a greater risk of root rot.
Pruning
No pruning needed. The modern hybrids are self-cleaning, dropping spent flowers on their own with no pinching or deadheading. The one job worth doing is pulling off declining leaves and blooms to keep disease from taking hold.
Size & spacing
Plants stay low and tidy, reaching 6 to 18 inches (15 to 46 cm) tall with a matching spread of about 8 to 18 inches (20 to 46 cm). Set them with enough room that air can move freely between plants, which goes a long way toward keeping the rots and leaf spots at bay.
When to plant
Annual vinca runs on heat and sulks in the cold. Sow seeds indoors in March where it's warm, then hold the plants back until late May or early June, well after frost and once the soil has warmed past 60°F (16°C). Set out too early into cool, wet ground and the plant stalls and rots; wait for the heat and it blooms from late spring all the way 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 problem with annual vinca traces back to one thing: water on the roots or the leaves. The rots strike from below in wet soil, while the leaf and gray-mold diseases ride in on splashed and standing moisture. Match what you see below, then dry the plant out and clear the infected tissue before it spreads.
Dark lesions on the stems with sudden wilting and collapse
This is Phytophthora stem blight and root rot, the disease that brings down more annual vinca than anything else, and wet soil with overhead watering sets it off. Dig up a failing plant and you'll find the outer root tissue sloughing away from the core while the leaves yellow and scorch. Pull and bin infected 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
Plants yellowing and wilting even though the soil is moist
When a plant fades in damp soil, suspect Rhizoctonia stem and root rot, which takes hold after deep planting or frequent shallow watering. Check the roots for brown lesions and stunting, the giveaway that moisture isn't the problem. Lift out the diseased plants with every last root, then drench or spray with thiophanate methyl or chlorothalonil.
Fix:
- Remove diseased plants completely including all roots
- Use thiophanate methyl or chlorothalonil as a spray or drench
Banded target-like spots creeping up from the lower leaves
These ringed spots are Alternaria leaf spot, splashed up onto the foliage by overhead watering. It starts on the bottom leaves as flecks no bigger than a pinhead, then grows to about an eighth of an inch with the telltale banded look and works its way up the plant. Strip out badly marked plants, water at the base before dawn, and spray chlorothalonil weekly if it spreads.
Fix:
- Remove heavily infected plants
- Apply weekly chlorothalonil sprays for serious infections
- Clear dead plants after frost
Fuzzy gray mold spreading over spent leaves and flowers
That fuzzy gray coating is Botrytis blight, also called gray mold, and it moves in during cool, damp spells on crowded plants. You'll see the heavy gray growth take over dead and dying tissue first. Keep picking off declining leaves and flowers as they appear, and reach for a thiophanate methyl spray only when an outbreak gets bad.
Fix:
- Remove declining leaves and flowers continuously
- Apply thiophanate methyl spray only if severe
Toxicity
This is a genuinely toxic plant, not one to take lightly. Every part holds vinca alkaloids such as vincristine and vinblastine, the same compounds used in cancer drugs, and there is no edible part to it. Eaten by a pet, animal, or child, it brings on drooling, vomiting, and diarrhea, with tremors, low blood pressure, and seizures possible after a large dose. Keep it well away from anyone, two-legged or four, who might be tempted to taste it.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
A cat that chews any part usually starts drooling, then vomits and develops diarrhea, often turning dull and listless. Larger mouthfuls can drop the blood pressure and trigger tremors or seizures, so call the vet without waiting it out.
Dogs Toxic
Dogs react with drooling, vomiting, and diarrhea soon after they nibble the leaves or flowers. Watch for a wobbly, depressed dog with low blood pressure, and treat tremors or seizures as an emergency.
Horses Toxic
Grazing horses get an upset gut, loose manure, and a flat, sluggish mood from the alkaloids. A big enough dose can bring on muscle tremors and serious weakness, so keep the plant well clear of pasture and paddocks.
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. This is not a safe plant to leave within reach of a hutch or a roaming bunny.
Livestock Toxic
Cattle, goats, and sheep that graze annual vinca take in vinca alkaloids that upset the stomach and sap their strength. Heavier feeding can lead to staggering and tremors, so fence it off from grazing animals.
Birds Toxic
Birds aren't spared either, since the alkaloids sit in leaves, stems, and flowers alike. Even a few pecked petals can bring on vomiting and weakness, so keep the plant out of aviaries and away from poultry.
People Caution
No part of annual vinca is meant to be eaten. Swallowing leaves or flowers can cause drooling, nausea, vomiting, and diarrhea, with tremors or low blood pressure after a large amount, so keep curious children and pets from tasting it.
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 done a lot with annual vinca, mostly to fight off disease and push the flowers bigger and bolder. These are the series you'll see most often.
Cora Group (Cora XDR)
This is the series to plant where rot is a problem, since it was bred to stand up to several strains of the Phytophthora root rot and aerial blight that hit annual vinca hardest.
Pacifica Group
A compact, well-branched bedding series that carries large flowers across a wide range of colors.
Titan Group
Mounded plants with very large flowers that hold up and keep performing through real summer heat.
Jams 'N Jellies Blackberry
Grown for its unusually dark blooms, a deep blackberry-purple set off by a clean white eye.
How to propagate
Annual vinca is grown from seed, and the one trick is warmth. Start it early indoors and resist the urge to rush it outside before the weather has truly 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 grows from seed, though it takes a warm start and some patience. Sow indoors in March and keep the tray genuinely warm, since cool seeds simply sit there. Give the seedlings several weeks to germinate and fill out, then hold them inside until late May or early June, once frost is past and the soil has climbed above 60°F (16°C).
Myths
Annual vinca is the same plant as the trailing groundcover periwinkle.
These are two different plants in the same 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 separate genus. They share the family Apocynaceae, but that's where the likeness ends.
Annual vinca needs frequent watering and deadheading to keep blooming.
It asks for the opposite. Heat and drought tolerant, it flowers nonstop from late spring to frost with no deadheading at all. Pour on extra water and you don't get more blooms, you get the root and stem rots that are its biggest weakness.