Periwinkle Catharanthus roseus Leisure and Cultural Services Department One Person, One Flower Scheme 2015/16 Periwinkle Catharanthus roseus

Periwinkle Scientific Name : Catharanthus roseus Common Names : Periwinkle or Madagascar Periwinkle Genus : Catharanthus Family : Apocynaceae (Dogbane) Distribution : Native to Madagascar, the plant is widely cultivated and naturalised in tropical and subtropical regions around the world.

Form and Characteristics Distribution : Tropical and subtropical regions Flower Colour : Flowers come in a myriad of colours including pink, dark red, mauve, deep purple, peach and white. Species plant has rosy pink flowers with a dark eye at the centre. Cultivated varieties are single- coloured or have a dark centre. Some of them produce larger flowers and some others have overlapping petals. Flowering Period : The plant enjoys a very long flowering period with almost continuous blooming.

Form and Characteristics An evergreen perennial herb or subshrub An erect, soft-stemmed plant that can grow to a height of 60 to 90 cm with a similar spread. Glossy and verdant leaves, about 5 to 7.5 cm long, are oblong or oblanceolate in shape and opposite with entire margins. The flowers grow in terminal or axillary cymes and have salverform corollas.

Form and Characteristics Some cultivars are hardier and suitable for growing in temperate climates. There are some erect cultivars and also some compact, dwarf cultivars which form ground covers or grow as trailing plants. Each flower usually develops a pair of follicles about 2.5 cm long with numerous small black seeds.

Horticultural Application Gardens Edging plant Ground cover Floral displays Flower beds Hanging baskets Xeriscape gardens Rooftop gardens

Growth Habits Prefers a warm tropical climate and full sun, with an optimum growth temperature of 15°C to 30°C. Can cope with partial shade. Intolerant to frost, has difficulty surviving the winter and can only be grown as an annual in temperate regions.

Growth Habits Tolerant to heat, drought and poor soils. The plant is not particular about soil. It flourishes in well-drained and humus-rich soil. Very drought-tolerant and can get by with little watering. If the soil is soggy or waterlogged, the plant will grow poorly; it may have rotten roots and end up withering.

Plant Care Periwinkle grown in pots should be pinched from time to time to promote shoot growth and keep the plant shapely. Old plants can be pruned in spring to help resume vigorous growth. Application of fertiliser in an appropriate amount after pruning can induce new shoots and encourage healthy plant growth, which is conducive to profuse flowering.

Plant Care The fruits of Periwinkle crack when mature. It is advisable to wait till the fruits have yellowed and pluck or snip them before they crack. This will prevent the seeds from spreading all over and growing into weeds.

Propagation – Seed Sowing Periwinkle is usually propagated by seeds. Seed sowing can be carried out in spring. The optimum temperature for germination is between 20°C and 25°C. Seeds are light-inhibited and should be covered with a thin layer of soil after being sowed. Keep the growing medium moist and the seeds will germinate in 7 to 10 days. After germination, the nursery tray can then be relocated to a brighter area under subdued light. The seedlings are ready for transplant as soon as 4 to 6 young leaves have emerged.

Potting Mix (for sowing) peat : vermiculite : perlite (1︰1︰1) sand : peat : river sand (1︰1︰1) river sand perlite peat vermiculite

Potting Mix (for long-term planting after transplanting) humus : peat : sand (2︰1︰1) peat : perlite : vermiculite (1︰1︰1) sand : peat : perlite (2︰1︰1) sand : peat : vermiculite (2︰1︰1) river sand perlite peat vermiculite

Propagation – Soft Tip Cutting Cutting can be carried out anytime during the growth period. The rooting medium should preferably be well-aerated, properly drained and clean sandy soil. Cutting should be conducted at a constant temperature of 20°C to 24°C. Select healthy and sturdy soft tips without flower buds as cuttings, each of which should be 10 to 12.5 cm long. Each cutting should have at least 3 to 4 nodes and preferably short internodes.

Propagation – Soft Tip Cutting Strip all but the top 3 to 4 leaves and insert the bottom one-third to half of the cuttings into the medium. Water the mixture thoroughly, then leave the cuttings in a partially shaded place for around one week before moving them to a brighter area under subdued light. Keep the medium moist throughout the period. Roots will develop in about 20 days and cuttings with vigorous root development can be transplanted for establishment.

Handling of Seedlings Watering Soil with adequate moisture is essential for healthy root growth in a newly re-potted or transplanted plant. Once the plant is established, it requires little fertiliser and water. The rooting medium should preferably be well-drained. If the soil is soggy or waterlogged, the plant will grow poorly; it may have rotten roots. Water the plants when the soil surface looks dry.

Handling of Seedlings Sunlight & Temperature Abundant sunlight is required for exuberant growth. Place them under sunlight for 8 to 10 hours a day. Insufficient sunlight will hamper flowering. The optimum growth temperature is 15°C to 30°C.

Handling of Seedlings Potting up The seedlings are ready for transplant as soon as 4 to 6 true leaves have emerged. Start pinching growing tips to promote the growth of branches and flowers. Transplant the seedlings into a pot with a diameter of 30 cm for long-term planting. After transplanting, water the plant immediately. Place the transplanted seedlings in a semi-shady area for 2 to 3 days and avoid direct sunlight. Thereafter, place them under sunlight for 8 to 10 hours a day to encourage growth and flowering.

Fertilising Apply chemical fertilisers containing Nitrogen(N), Phosphorous(P) and Potassium(K) (Quick-acting fertilisers). NPK (Nitrogen:Phosphorous:Potassium) ratio should be 10:30:20. Do not apply too much nitrogen fertiliser (which stimulates leaf growth) as it will lead to the overgrowth of stems and leaves and hamper flowering. The pedicels, growing too tall and soft, may easily topple.

Fertilising After transplanting, apply organic matter or slow-release inorganic fertiliser as a base fertiliser. Apply fertiliser once every 3 to 4 weeks during the growth period. Frequent light applications are preferred. Apply fertiliser moderately after pruning to encourage healthy plant growth.

Prevention and Treatment of Pests and Diseases Periwinkle is rarely affected by pests or diseases but is sensitive to excessive moisture. To ensure healthy growth free from infection: Keep the soil well-drained and avoid over-watering. Apply only the appropriate amount of fertiliser. Loosen the soil and weed regularly. Ensure sufficient light and space for the plant. Keep the growing environment clean and well-ventilated.

Points to Note Like many other plants in the Apocynaceae family, the broken stem of Periwinkle exudes a milky latex. The plant can cause allergy in some people. Be careful when handling it: Wear gloves and wash hands immediately afterwards. Withered flowers should be pinched off promptly to encourage the growth of flower buds. Do not re-pot during the flowering period. Prune the plant back after flowering.

Visit the following website for more information about Periwinkle: http://www.lcsd.gov.hk/en/green/education/greeningschool/one.html