How to Grow Bengal Clock Vine | Thunbergia Grandiflora Care

With its vibrant, trumpet-shaped blooms in shades of blue, purple, pink and white, it’s easy to see why Bengal clock vine (Thunbergia grandiflora) has become a beloved ornamental plant. This fast-growing tropical vine offers season-long color and is well-suited for gardens in USDA zones 9-11.

Though often grown as an annual in cooler climates, Bengal clock can thrive for many years in the right conditions. Read on to learn more about how to successfully grow and care for this eye-catching beauty.

Bengal Clock Vine – Key Facts

Overview of Bengal Clock Vine

Native to eastern India, Bengal clock vine is classified as a tender perennial. It’s an evergreen climbing vine in the Acanthaceae family. Some other common names include blue sky vine, blue thunbergia and clock vine.

Mature plants can grow quite large, easily reaching 10 feet (3 m) or more in height. The lush, heart-shaped leaves provide a nice backdrop for the abundant trumpet-like flowers that bloom spring through fall.

Flowers come in blue, purple, pink, white and bi-colored varieties. The most common is a vibrant sky blue. Blooms open fully in morning sunlight, then fold up partially during the afternoon before closing at night.

This fast growth rate, long bloom season and adaptability to containers make Bengal clock vine a great choice for trellises, arbors, fences and more. It also works well in hanging baskets.

Growing Conditions

Bengal clock thrives with full sun exposure and humid warmth. Providing the right cultural conditions is key to a healthy, floriferous vine.

Sun Exposure

• Full sun is ideal, with at least 6 hours of direct sunlight per day
• Partial shade may work but can result in fewer blooms
• More shade-tolerant in hot climates
• Needs consistent sunlight for best flowering

Soil

• Thrives in moist, humus-rich, well-draining soil
• Loam or sandy loam soils amended with compost work well
• Neutral to slightly acidic pH between 6.0-7.0
• Doesn’t tolerate salty or alkaline soils

Water

• Moderate but regular watering required
• Soil should be kept evenly moist but not saturated
• Allow soil surface to partly dry out between waterings
• Avoid drought stress

Temperature & Humidity

• Prefers warm weather 70-90°F (21-32°C)
• Can tolerate short spells of cooler temps above 55°F (13°C)
• High humidity encourages lush growth and flowering
• Does poorly in arid climates with low humidity

How to Plant

Bengal clock vine can be started from seeds, cuttings or purchased as young plants. Follow these tips for successful planting.

Starting from Seed

• Sow indoors 8-10 weeks before last expected frost
• Use moist seed starting mix and keep evenly moist
• Germination takes 14-21 days at 70-75°F (21-24°C)
• Transplant seedlings when 2-3 true leaves emerge
• Harden off before transplanting outdoors after frost risk passes

Transplanting Seedlings

• Space 12-18 inches apart in garden after hardening off
• Dig holes twice the width of the root ball
• Gently loosen root ball and place in hole so top is level with soil
• Backfill with native soil and pat down gently
• Water thoroughly after transplanting

Established Plants

• Plant in spring after threat of frost has passed
• Space 2-3 feet apart in well-draining soil
• Dig wide, shallow holes and loosen roots before planting
• Water well and continue with moist soil until established
• Provide support or trellis for vines to grow on

Care and Maintenance

A few simple care practices throughout the season will keep your Bengal clock vine thriving.

Training and Support

• Install trellises, nets, strings or other structures for vines to climb
• Train vines upward early to encourage vertical growth
• Add intermediate support on fences or railings to prevent sagging
• Pinch off wayward stems to train vines where wanted

Fertilizing

• Apply balanced liquid fertilizer every 2-3 weeks during growth
• Use 1⁄2 strength dilution to avoid fertilizer burn
• Switch to blossom booster fertilizer when buds appear
• Stop fertilizing by early fall to harden off for winter

Pruning

• Prune lightly in spring to shape vines and improve air circulation
• Remove dead or damaged growth as needed
• Cut back longer vines by 1/3 their length to encourage branching
• Avoid heavy pruning that removes too much foliage

Pest and Disease Control

• Monitor for common issues like aphids, whiteflies, powdery mildew
• Remove pests with pressure spray of water or insecticidal soap
• Improve airflow and avoid excess moisture to prevent mildew
• Use neem oil or sulfur sprays to treat fungal diseases
• Disinfect tools between plants to limit spread of diseases

Tips for Maximizing Growth and Blooms

Follow these tips to keep your Bengal clock vine thriving and floriferous:

• Plant in fertile, humus-rich soil amended with compost or manure
• Install trellises or other vertical supports early to encourage upward growth
• Prune lightly in spring and remove dead stems to improve air circulation
• Water thoroughly and often enough to maintain moist (but not soaked) soil
• Fertilize every 2-3 weeks during active growth and blooming
• Protect vines from strong winds which can damage stems and flowers
• Grow in bright, full sun locations for optimal flowering
• Provide afternoon shade in hot summer climates
• Increase humidity with misting, pebble trays or nearby water features
• Deadhead spent blooms to encourage continuous flowering

Propagation

Bengal clock vine is easy to propagate from cuttings, layering or division.

From Cuttings

• Take 6-8 inch tip cuttings from healthy vines in spring
• Strip lower leaves and dip cut end in rooting hormone
• Plant in seed starting mix and keep humid
• Rooting takes 4-6 weeks at 70°F (21°C)
• Transplant rooted cuttings to garden after hardening off

Layering

• Choose a low-growing stem and wound the middle
• Pin that section to the ground and cover with soil
• Keep soil moist until new roots and shoots form
• Sever the rooted stem and transplant

Division

• Division is done by carefully digging up an established plant and gently separating the root mass into smaller sections.
• Use your hands or a sharp, sterilized knife to tease apart the roots. Avoid ripping or tearing roots.
• Each divided section should have some roots and one or more shoots.
• Replant the divisions into pots or the garden, spacing them apart.
• Water the divisions thoroughly after replanting to remove air pockets in soil.
• Keep the divisions well-watered until they are re-established. New growth will emerge within a few weeks.
• Division is best done in early spring when plants are entering active growth. It gives them time to regenerate before summer.
• Dividing congested plants helps rejuvenate them and encourages bushier, healthier growth. It’s a simple, effective way to propagate more vines.

Common Problems

Bengal clock vine is relatively trouble-free but may experience issues like:

• Leaf spots – Fungal diseases that cause round brown spots on foliage. Improve air circulation and avoid wet leaves.
• Powdery mildew – White fungal coating on leaves, stems and flowers. Favorable in humidity. Improve air flow and reduce moisture.
• Aphids – Small sucking insects that feed on new growth. Knock off with jets of water or use insecticidal soap sprays.
• Mealybugs – White cottony insects that feed on sap. Remove manually or use horticultural oil sprays.
• Snails/slugs – Slimey pests that chew holes in leaves. Remove by hand or use iron phosphate baits.

The main solutions are improving air circulation, reducing moisture on foliage, promptly removing pests, and using organic fungicides/insecticides when needed. Address issues promptly to avoid major infestations.

Improve airflow and drainage and promptly remove affected foliage or pests to prevent major problems.

Conclusion

With its fast, lush growth and long season of abundant blooms, it’s easy to see the appeal of Bengal clock vine. By providing the right growing conditions and care, gardeners can enjoy this tropical beauty even in colder climates. A little effort goes a long way in cultivating a thriving and floriferous clock vine that will elevate gardens and landscapes with its vibrant color and tropical essence.

Frequently Asked Questions

What are the best uses for Bengal clock vine?

Bengal clock vine shines in garden beds, borders, containers, and anywhere it can climb upwards with support. Popular uses include training it on arbors, trellises, fences, railings, and other structures. It also works well in hanging baskets.

How fast does Bengal clock vine grow?

Bengal clock vine grows rapidly, easily reaching 10 feet (3 m) or more in a single season. Growth rate is maximized in full sun and warm temperatures with adequate moisture. Prompt pruning keeps growth tidy.

What is the best way to overwinter Bengal clock vine

?In zones 9-11 where it is perennial, Bengal clock vine will die back with frost but regrow from the roots each spring. Provide winter mulch in colder areas. In zones 8 and below, grow it as an annual or bring pots indoors before frost.

Why are the leaves turning yellow?

Stressed, yellowing leaves can result from issues like overwatering, drought, extreme heat or cold. Improve drainage in soggy soils and avoid dry spells. Provide shade in hot climates and bring indoors or mulch before frost.

How can I encourage more blooms?

Maximize sunlight, warmth, humidity and fertile soil. Fertilize regularly during growth and blooming. Prune lightly in spring to encourage new growth. Deadhead spent blooms to promote reblooming. Avoid excess shade and drought stress for prolific flowers.