Germination temperature
Warm: at least 21-24 °C (70-75 °F); laboratory germination was highest at 25-35 °C (77-95 °F).
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Madagascar periwinkle, also sold as annual vinca, germinates best warm and in darkness, and its seedlings rot easily if they are kept too wet. This guide covers sowing, watering and the safety points every grower should know.
Warm: at least 21-24 °C (70-75 °F); laboratory germination was highest at 25-35 °C (77-95 °F).
Cover lightly, just enough to keep the seed in the dark.
About 7-14 days in warmth.
Keep the seed dark until it germinates; give full light straight after.
None needed.
Usually raised in trays; seedlings are slow and need about 10 weeks before planting out.
Sow fresh, dry seed. Vinca seed loses germination when stored humid: in trials it kept well for 12 months at 5 °C (41 °F) at low humidity, but more than a month at 75% relative humidity or above reduced germination. In humid climates store the packet sealed in a cool, dry place.
Not needed. The seed has no hard coat.
Not needed. This is a tropical plant; cold delays and reduces germination.
Not needed, and wet seed is more prone to rot. Sow dry onto moist compost.
Extension guidance gives 21-24 °C (70-75 °F). In laboratory tests in darkness, germination was equally high at 25, 30 and 35 °C (77, 86 and 95 °F), fastest within that range, and lowest below 25 °C (77 °F). Warm Indian conditions suit it well; in cool rooms use a warm spot or a heat mat.
Cover the seed lightly with fine compost or vermiculite, just enough to exclude light, and keep it close to the surface.
A free-draining seed compost. Good drainage matters more than richness, because damp, airless compost leads to damping off.
Moist but never soggy. Overwatering is the most common cause of failure with this plant.
Madagascar periwinkle germinates in darkness: keep trays covered with dark paper or in a dark, warm place until the seedlings emerge, then move them into bright light at once so they do not stretch.
About one week at 21-24 °C (70-75 °F) in good conditions, and up to about two weeks; cooler compost slows it down.
Plant out once warm weather has settled, when seedlings are about 10 weeks old. Space plants 30-45 cm (12-18 in) apart, in full sun or partial shade, at the same depth they grew in the tray. Planting too deep encourages stem rot.
Seedlings grow slowly at first, and plants raised from seed take a long time to flower. Keep them warm and bright, and water only when the surface begins to dry.
Cause: damping off from Pythium in wet compost. Fix: use clean trays and fresh compost, water from below or thoroughly but less often, and give good air movement.
Cause: Phytophthora root rot and stem blight, encouraged by frequent watering. Fix: plant in well-drained soil or raised beds, water only when needed, and remove affected plants. Some modern cultivars are bred for resistance.
Cause: Rhizoctonia, favoured by light, frequent watering and planting too deep. Fix: plant at the original depth and water deeply but infrequently.
Cause: Botrytis in cool, damp weather. Fix: wait until warm weather persists before planting out and remove dead flowers and leaves.
Madagascar periwinkle is a warm-season plant that tolerates heat and drought. In most of India it can be sown in the warm months; during the monsoon grow it in pots or raised beds so the roots never stand in water.
Established plants are drought tolerant. Cut back watering once they are growing well, especially in the rainy season.
All parts of the plant contain vinca alkaloids. Eating it, especially in larger amounts, can cause poisoning, so grow it where children and pets will not chew it, and never use it as a home remedy.
Annual vinca (Catharanthus roseus) is a different plant from the ground-cover periwinkles of the genus Vinca. Check the botanical name when buying seed or advice.
Sow Madagascar periwinkle seeds for heat-tolerant flowers through the warm season.
Darkness. Cover the seed lightly and keep the tray dark and warm until seedlings emerge, then move it into bright light straight away.
Usually overwatering. Wet compost leads to damping off and root rots caused by Pythium, Phytophthora and Rhizoctonia. Use a free-draining mix, water thoroughly but less often, and keep air moving.
Yes. All parts contain vinca alkaloids, and eating the plant, especially in larger amounts, can cause poisoning. Keep it away from children and pets.