Why Are My Bidens Leaves Curling?

Overwatering and root rot

Despite its reputation as an easy-going, vigorous trailing plant, bidens does not tolerate persistently wet compost. Its fine root system is susceptible to oxygen deprivation and rot in saturated compost, particularly during cooler, overcast periods when evaporation from the basket is reduced. A plant with rotting roots cannot absorb water or nutrients even in wet compost, so the feathery leaves wilt, curl, and lose their fresh green colour. The basket feels heavy because it is full of wet compost, yet the plant looks as though it is dying of thirst.

What to do

• Water only when the top 2 cm of compost feel dry. Reduce watering frequency significantly during cool or overcast spells.
• Ensure baskets and containers have adequate drainage. Avoid liners that hold excessive moisture, particularly solid plastic liners with no drainage holes.
• Use a free-draining, peat-free compost with added perlite rather than a moisture-retentive mix for baskets.
• If root rot is established, remove the plant, trim away any soft and rotting root material, and replant in fresh, well-aerated compost.

Spider mite infestation

Spider mite is a significant pest on bidens, particularly during hot, dry summers and in sheltered positions where air humidity is low. The mites feed on the undersides of the feathery leaves, causing the upper surface to develop fine bronze or silvery stippling. The affected leaves curl, lose their vibrant green colour, and the plant's overall vigour declines. In heavier infestations, fine webbing becomes visible between the leaves and along the stems, and flowering decreases markedly.

Bidens grown in hanging baskets in hot, sunny positions are particularly vulnerable as the basket dries out quickly, creating the warm, dry conditions that spider mites love.

What to do

• Inspect the undersides of curling leaves for the tiny reddish or yellowish mites and their webbing.
• Spray the plant thoroughly with a strong jet of water, targeting the undersides of the feathery leaves.
• Follow up with insecticidal soap or neem oil spray every five to seven days for four to six weeks, ensuring thorough coverage of the fine foliage.
• Misting the foliage regularly and keeping the plant consistently moist creates conditions less favourable to mite reproduction.

Underwatering

Bidens is more tolerant of brief drought than some basket plants, but it still requires consistent watering in containers to flower well through the season. When the compost dries out completely, the fine leaves wilt and curl and the plant may temporarily drop flowers and buds. Recovery is usually rapid once watered. Repeated cycles of severe drying out and re-watering weaken the plant over time and make it more susceptible to spider mite.

What to do

• Water when the top 2 cm of compost feel dry. In hanging baskets on warm, sunny days, this may mean daily watering.
• Incorporating water-retaining gel into the compost at planting significantly reduces watering frequency and the risk of drought stress.
• After severe drying out, water slowly and thoroughly to ensure moisture reaches the full depth of the basket rather than running straight through.

Aphid infestation

Aphids occasionally colonise bidens, particularly in sheltered positions in spring. They cluster on the soft shoot tips and the undersides of young feathery leaves, and their feeding causes distortion and curling of the new growth. Because the leaves are so finely divided, aphid colonies can be hard to spot until the damage is already visible. Green and black aphids are the most common species encountered on bidens.

What to do

• Pinch out and remove shoot tips with the heaviest aphid colonies.
• Spray with insecticidal soap every four to five days for two to three weeks, ensuring thorough coverage of the fine foliage and the shoot tips.
• A jet of water from a hose dislodges most aphid colonies quickly before chemical treatment.

Nutrient deficiency

Bidens is a vigorous, fast-growing plant that depletes container compost nutrients quickly. Without regular liquid feeding, the leaves gradually lose their deep green colour, become pale and slightly curled, and flowering diminishes. Potassium deficiency specifically causes the leaf edges to turn yellow or brown and curl. Slow-release fertiliser incorporated at planting provides a good foundation but should be supplemented with regular liquid feeding through the season.

What to do

• Feed bidens in containers every one to two weeks with a balanced or high-potassium liquid fertiliser throughout the growing season.
• A tomato fertiliser, applied at the manufacturer's recommended rate, provides the potassium that encourages prolific flowering.
• If the compost is older than six to eight weeks and has never been supplemented with liquid feed, pale and poor-looking growth is likely primarily a nutrient issue.

Frequently asked questions

Why are my bidens leaves curling?

Bidens leaves curl most often from overwatering and root rot or from spider mite infestation. The fine, feathery leaves wilt and curl when the compost is persistently wet and the roots cannot function. Spider mite causes stippling and curling of the leaves alongside fine webbing on the undersides, particularly in hot, dry conditions.

How often should I water bidens?

Water bidens when the top 2 cm of compost feel dry. It needs consistent moisture but the roots must not sit in waterlogged compost. In hanging baskets in warm weather, this typically means watering every one to two days. Bidens is moderately drought tolerant compared to other basket plants and recovers well from brief drying out.

Why is my bidens getting leggy and the leaves are curling?

Legginess combined with curling leaves suggests the plant is under stress from overwatering, nutrient deficiency, or insufficient light. Cut the stems back by about one third to encourage bushy, compact regrowth. Feed with a high-potassium liquid fertiliser and ensure the plant receives adequate direct sunlight.

Does bidens need deadheading?

Bidens is largely self-cleaning and does not need regular deadheading to continue flowering. It produces small yellow daisy flowers in great abundance and naturally drops spent blooms. However, trimming back overly long stems periodically keeps the plant compact and encourages fresh flowering growth from the base.