Ornamental · Apocynaceae
Annual Vinca
Catharanthus roseus
Hand it heat, blazing sun, and dry-side soil, and annual vinca powers out blooms from late spring to frost.
Full sun
Every 5–10 days
50–95°F · 10–35°C
USDA 10–11
Overview
Here is a plant that thrives exactly where others throw in the towel. Annual vinca, or Madagascar periwinkle, loves the hot, sun-drenched, dry corners of the garden and answers them with bloom after bloom from late spring clear to frost. The flowers roll out in whites, pinks, and a knockout deep blackberry-purple, every one popping against glossy dark green leaves. Worth flagging right away: this is Catharanthus roseus, not the trailing periwinkle it constantly gets mistaken for.
The best part is how tough it is, though that toughness comes with one catch. It is so heat and drought tolerant that overwatering, not neglect, is the thing that trips growers up. Keep the soil soggy and you hand it the root and stem rots that are its one real weak point, and those rarely let a plant bounce back.
Grow it as the warm-season annual it is and it practically runs itself. Hold out for real summer heat, plant it in full sun and fast-draining soil, and water only when it truly asks. Nail that and you get months of nonstop color from a plant that gives back way more than it takes.
Care
The short version: full sun, fast-draining soil, and genuine summer warmth before you plant. Water deeply but only once the top of the soil dries out, keep the leaves dry, and go light on the fertilizer.
Light
Pour on the full sun and annual vinca flowers its heart out, though it will take a little partial shade in stride. Load it up with direct light for a dense, flower-packed plant; drop it into shade and it thins out and loses its punch.
Water
Water it deep but rarely, stepping in only when the week's rainfall dips under about an inch. Let the top half of the soil dry between drinks and keep water off the leaves, because soggy roots and wet foliage are exactly what disease jumps on.
Soil
Set it in fast-draining soil, sandy or organic loam, and it will even shrug off clay as long as water keeps moving. It powers along best in slightly acidic ground, a pH of 5.5 to 6.5.
Temperature
This is a full-on heat lover, cruising from 50°F to 95°F (10°C to 35°C) and hitting its stride at the top of that range. Cold puts the brakes on and damp chill invites rot, so it truly comes alive through the hottest stretch of summer.
Humidity
Everyday outdoor humidity is plenty, so skip chasing a number. Moving air does the heavy lifting, since still, muggy air in a crowded planting is what lets leaf spot and gray mold dig in.
Feeding
Feed it monthly through the growing season with a balanced general-purpose fertilizer, and keep the dose light. Overfeed and you swap flowers for soft growth and a bigger shot at root rot, which is nobody's idea of a win.
Pruning
Great news, there is nothing to prune. The modern hybrids are self-cleaning and toss their spent flowers on their own, no pinching or deadheading required. The one job worth doing is stripping off tired leaves and blooms so disease never gets a grip.
Size & spacing
These stay compact and punchy, topping out around 6 to 18 inches (15 to 46 cm) tall and spreading roughly 8 to 18 inches (20 to 46 cm) wide. Space them so air can whip between the plants, and you knock back the rots and leaf spots before they start.
When to plant
Annual vinca runs on heat, plain and simple, and it stalls the moment things turn cold. Fire up seeds indoors in March somewhere warm, then hold the plants back until late May or early June, well past frost and once the soil breaks 60°F (16°C). Rush them into cold, wet ground and they sulk and rot, but give them the heat and they bloom from late spring straight 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
Almost every hiccup with annual vinca traces back to one thing: water sitting on the roots or the leaves. Soggy soil sends the rots up from below, while splashed and standing water spreads the leaf spots and gray mold. Track down your symptom below, then dry the plant out and strip the infected tissue before it runs.
Dark stem lesions, then a fast wilt and collapse
A plant that suddenly folds with dark stem lesions has run into Phytophthora stem blight and root rot, the top killer of annual vinca, and wet soil plus overhead watering fires it up. Yank a failing plant and you will catch the outer root tissue peeling off the core while the leaves yellow and scorch. Rip out and bin the sick plants, dig composted pine bark into the bed for drainage, then hit it 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 even with moist soil
When a plant crashes in soil that is still damp, point the finger at Rhizoctonia stem and root rot, which pounces after deep planting or frequent shallow watering. Pop a plant out and the roots give it away, brown lesions and stunting that prove water was never the issue. Haul out the sick plants, every root included, 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
Ringed target spots marching up from the lower leaves
Those ringed, bullseye spots are Alternaria leaf spot, and overhead watering flings it right onto the foliage. It fires up on the bottom leaves as pinhead flecks, swells to about an eighth of an inch with the banded look, and climbs the plant. Pull the badly marked ones, water at the base before dawn, and blast it with chlorothalonil weekly if it keeps moving.
Fix:
- Remove heavily infected plants
- Apply weekly chlorothalonil sprays for serious infections
- Clear dead plants after frost
Fuzzy gray mold overrunning spent leaves and flowers
That fuzzy gray layer is Botrytis blight, aka gray mold, and it rolls in during cool, damp spells on crowded plants. Watch it grab the dead and dying tissue first. Keep snapping off tired leaves and flowers as they turn, and only grab a thiophanate methyl spray if an outbreak really takes off.
Fix:
- Remove declining leaves and flowers continuously
- Apply thiophanate methyl spray only if severe
Toxicity
As fun as it is to grow, this one demands real respect. Every part packs vinca alkaloids like vincristine and vinblastine, the same compounds behind certain cancer drugs, and nothing on it is edible. If a pet, animal, or child eats some, expect drooling, vomiting, and diarrhea, and after a big dose maybe tremors, low blood pressure, or seizures. Keep it well clear of anyone tempted to take a bite.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
A cat that chews any part usually starts drooling fast, then vomits and gets diarrhea, and often turns dull and listless. A bigger mouthful can drop the blood pressure and set off tremors or seizures, so skip the wait-and-see and call the vet.
Dogs Toxic
A dog that grabs the leaves or flowers quickly drools, vomits, and gets diarrhea. Keep an eye out for a wobbly, flattened dog with low blood pressure, and treat any tremors or seizures as a flat-out emergency.
Horses Toxic
A grazing horse ends up with an upset gut, loose manure, and a flat, sluggish mood from the alkaloids. Enough of it can spark muscle tremors and serious weakness, so keep this plant well away from pasture and paddock.
Rabbits Toxic
The same alkaloids run through every part, so a rabbit that browses the leaves can wind up drooling, with diarrhea and a slumped, low-energy droop. This is no plant to leave anywhere near a hutch or a roaming bunny.
Livestock Toxic
Cattle, goats, and sheep that graze annual vinca load up on vinca alkaloids that upset the stomach and drain their strength. Heavier feeding can send them staggering and trembling, so fence it off from grazing animals.
Birds Toxic
Birds get no free pass either, since the alkaloids sit in the leaves, stems, and flowers alike. Even a few pecked petals can trigger vomiting and weakness, so keep it clear of aviaries and away from poultry.
People Caution
Nobody should be eating any part of this plant. Down the leaves or flowers and you can get drooling, nausea, vomiting, and diarrhea, plus tremors or low blood pressure after a big amount, so keep it out of reach of curious kids 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
Breeders have thrown plenty of energy at annual vinca, chasing tougher disease resistance and bigger, showier flowers. These are the series you will run into most.
Cora Group (Cora XDR)
Grab this series for anywhere rot keeps striking, since breeders armed it against several strains of Phytophthora, the root and aerial rots that hit this plant the hardest.
Pacifica Group
A compact, bushy bedding series that pumps out big flowers across a huge spread of colors.
Titan Group
A mounding series loaded with oversized flowers that keep charging through blistering summer heat.
Jams 'N Jellies Blackberry
The showstopper for dark color, a deep blackberry-purple bloom lit up by a crisp white eye.
How to propagate
Fancy raising more? Annual vinca grows from seed, and the whole game is warmth. Kick it off early indoors, and hold your nerve until the weather truly heats up before it goes outside.
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, and the one thing it demands is warmth. Start it indoors in March and keep that tray toasty, because cool seed just stalls out. Give the seedlings their several weeks to sprout and bulk up, then keep them inside until late May or early June, once frost clears and the soil pushes past 60°F (16°C).
Myths
Annual vinca is just the trailing groundcover periwinkle wearing a different name.
Not a chance, these are two separate plants that only share a family. Annual vinca is Catharanthus roseus, an upright to mounding warm-season bedding flower, while the creeping perennial groundcovers are Vinca minor and Vinca major from their own genus. Yes, both land in Apocynaceae, but that is where the family resemblance quits.
Annual vinca needs constant watering and deadheading to keep the show going.
It actually wants the flip side of that. Being heat and drought tolerant, it cranks out flowers from late spring to frost with zero deadheading. Keep hosing it down and you win no extra blooms, just the root and stem rots that are its biggest weak spot.