Why Are My Catharanthus Leaves Curling?

Aphid infestation

Aphids colonise catharanthus at the shoot tips and on the undersides of the glossy leaves, causing the young leaves to curl and the shoot tips to distort. Green peach aphid and cotton aphid are both found on catharanthus in UK gardens. Because the plants are dense and bushy, aphid colonies can become established in the interior of the plant before being noticed from the outside. Heavy infestations slow growth and reduce flowering.

What to do

• Inspect the shoot tips and the undersides of leaves regularly, particularly on young plants in early summer.
• Spray with insecticidal soap every four to five days for two to three weeks, covering the undersides of leaves and shoot tips thoroughly.
• A strong jet of water dislodges aphids from the glossy leaves effectively before applying chemical treatment.

Cold stress

Cold stress is the most common cause of catharanthus failure in UK gardens. As a tropical plant from Madagascar, catharanthus requires sustained warmth to thrive: temperatures below 10 degrees Celsius at night cause the glossy leaves to curl, yellow, and develop bronze or reddish discolouration. Plants exposed to temperatures below 5 degrees suffer significant damage and often fail to recover. Cold stress mimics the symptoms of overwatering and root rot, making it important to consider temperature as a possible cause before concluding that a root problem is responsible.

What to do

• Do not plant catharanthus outside until late May or early June when nighttime temperatures are reliably above 12 degrees Celsius.
• Choose the warmest, most sheltered position available: catharanthus is an excellent plant for a south-facing container or for a patio against a warm wall.
• Harden off plants thoroughly for two weeks before planting out, starting with daytime outdoor exposure only.
• Move containers under cover if cold nights are forecast in summer. Cold-stressed plants often recover if returned to warmth quickly.

Overwatering

Catharanthus is highly sensitive to overwatering and root rot, more so than many other common bedding plants. In persistently waterlogged compost, the roots deteriorate rapidly and the whole plant declines: the glossy leaves yellow, curl, and drop, and the stems may become soft at the base. This is particularly common in the UK where cool, cloudy weather can follow sunny spells, leaving compost that was appropriate to water during hot weather now staying wet for far too long. Root rot is one of the most common causes of sudden catharanthus failure.

What to do

• Use a free-draining, peat-free compost blended with perlite for catharanthus in containers. Ensure excellent drainage holes.
• Water only when the top 2 to 3 cm of compost feels dry. Never keep the compost consistently moist.
• Reduce watering significantly during cool, overcast, or wet periods.
• Raise containers on pot feet to allow excess water to drain freely and prevent waterlogging at the base.

Drought stress

While catharanthus is more heat and drought tolerant than many bedding plants, prolonged water stress causes the glossy leaves to curl and the plant to drop flower buds before they open. The glossy surface of the leaves slows water loss but does not prevent it entirely, and container-grown plants in full sun in hot weather can dry out rapidly. The key with catharanthus is to water thoroughly when needed, then allow the surface of the compost to dry before watering again.

What to do

• Water catharanthus thoroughly when the top 2 to 3 cm of compost feel dry. The roots benefit from deep watering that encourages deeper root development.
• Feed with a balanced liquid fertiliser every two weeks through the growing season to support continuous flowering.
• In very hot, sunny positions, check the compost moisture daily and water before the plant shows stress symptoms.

Iron deficiency

Catharanthus grown in very alkaline compost or in calcareous garden soil can develop iron deficiency chlorosis: the younger leaves turn pale yellow between the veins while the veins themselves remain green, and the affected leaves may curl slightly at the margins. The plant looks progressively weaker and produces fewer flowers. This is particularly likely in areas with naturally chalky or limestone soil, or when plants are grown in a compost with a very high pH.

What to do

• Use an ericaceous or slightly acidic compost for catharanthus in containers, or blend standard compost with sulphur chips to lower the pH.
• Apply a chelated iron feed according to the label directions at the first signs of chlorosis. This provides iron in a form available to the plant even in slightly alkaline conditions.
• Avoid liming the soil around catharanthus and do not use hard, alkaline tap water for repeated watering if possible.

Frequently asked questions

Why are my catharanthus leaves curling?

Catharanthus leaves curl most often from aphid infestation or cold stress. Aphids colonise the shoot tips and the undersides of the glossy leaves, causing them to curl and distort. Cold nights below 10 degrees Celsius cause the leaves to curl, yellow, and develop a bleached appearance, as catharanthus is a warm-season tropical plant that performs poorly in cool conditions.

Why are my vinca leaves turning yellow and curling?

Yellow curling leaves on catharanthus most often indicate overwatering, iron deficiency in alkaline soil, or cold stress. Catharanthus is very sensitive to waterlogged roots and the foliage yellows quickly when the compost is kept too wet. It also develops chlorosis in very alkaline soil where iron becomes unavailable. Cold nights below 10 degrees Celsius cause yellowing and curling of the glossy leaves.

Is catharanthus the same as vinca?

Catharanthus roseus (Madagascar periwinkle) is a different plant from the garden vinca (Vinca minor and V. major), though the two share the common name periwinkle and have superficially similar flowers. Catharanthus is a half-hardy annual from Madagascar grown for summer bedding. The hardy vincas are evergreen perennial ground covers from Europe. They are not related.

How do I keep catharanthus flowering all summer?

Catharanthus is largely self-cleaning and deadheads itself, so minimal intervention is needed to maintain continuous flowering. Consistent moisture, fortnightly feeding with a balanced liquid fertiliser, and a warm, sunny, sheltered position are the main requirements. Avoid overwatering and cold temperatures, which are the most common causes of poor performance.