Blue sky vine

Sun

Full sun to partial shade; afternoon shade helps in very hot, dry locations. Indoors, provide strong light.

Water

Water deeply during active growth, keeping the root zone moist but not waterlogged. Reduce watering in winter, especially under cool indoor conditions.

Soil

Fertile, moisture-retentive soil with good drainage; use a free-draining potting mix in containers.

Height

20-40 ft (6-12 m), potentially taller in tropical conditions

Spread

6-15 ft (1.8-4.6 m), wider if left uncontrolled

Flowers

Pale blue to lavender trumpet-shaped flowers with creamy yellow throats, mainly summer to autumn; flowering can continue much longer in tropical climates.

Foliage

Evergreen. Large, rough-textured green leaves, usually heart-shaped with angular or shallowly lobed edges.

Growth

Fast in warm weather

Care needed

High

• Pollinators
• Heat tolerant
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Hard

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   2 ft (0.6 m)

2. After 1 year

   3 ft (1.1 m)

3. After 2 years

   5 ft (1.5 m)

4. After 3 years

   6 ft (1.8 m)

   full size

About 3 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Invasive in

the US and Australia

In the garden

Spreads vigorously: plan to contain it.

Growth rate

Fast

• Provide a strong pergola or trellis and tie young shoots in before they become tangled.
• Water deeply when the soil surface starts to dry; empty container saucers after watering.
• Feed container plants with a balanced liquid fertiliser during active growth, following the label rate.
• Mulch the root zone, keeping mulch clear of the stems.
• Bring container plants indoors before frost and overwinter in bright conditions, preferably above 50°F (10°C).
• Inspect surrounding ground for rooted stems and unwanted shoots; remove them promptly.

Pruning. In late winter or early spring, remove dead and tangled stems and shorten vigorous growth to fit its support. Trim escaping shoots during the growing season, and do not leave cut stems on moist ground where they may root.

Late winter

Prune established plants before strong new growth begins and inspect the support for damage.

Spring

Refresh container compost or repot if root-bound, then resume feeding as growth starts.

Late spring

After frost risk has passed and nights are consistently warm, gradually acclimatise overwintered plants to outdoor conditions.

Summer

Water regularly, tie in new shoots and cut back growth that reaches gutters, trees or neighbouring plants.

Early autumn

In cool climates, check plants for pests and bring them indoors before cold nights.

Winter

Keep sheltered plants in bright light and water sparingly without allowing the root ball to dry out completely.

• Train over a substantial pergola in a frost-free garden so the flower clusters hang below the framework.
• Use on a freestanding trellis as a leafy screen, with room to prune both sides.
• Grow in a large container with a sturdy support on a warm terrace, allowing for indoor winter storage.
• Pair with bold-leaved tropical plants for contrasting leaf shapes and a cool blue flower colour.

Garden styles it suits: Tropical, Modern tropical, Luxury resort, Modern courtyard, Romantic rose garden and Blues and silvers.

Plant it with: Canna, Ginger lily, Elephant's ear, Clivia and Bird of paradise.

Wildlife: Flowers attract bees and other nectar-feeding insects. In invaded habitats, dense growth can smother native vegetation and reduce habitat quality.

• Uncontrolled growth: stems can overwhelm shrubs and small trees; use a separate strong support and prune escaping growth frequently.
• Red spider mites: common under warm, dry cover; rinse leaf undersides and use an appropriate insecticidal soap or biological control if needed.
• Whitefly or scale insects: inspect sheltered plants regularly, remove heavily affected shoots and treat with a labelled horticultural soap or oil.
• Yellowing and root rot in wet soil: improve drainage, empty saucers and reduce watering during cool weather.

Not known to be toxic to people, cats, dogs or horses, but reliable species-specific toxicity information is limited. No part should be treated as edible.

Where it spreads. Spreads aggressively in humid tropical and subtropical climates, including Hawaii, Florida and parts of northern Australia. It is a regulated invasive plant in Queensland, the Northern Territory and Western Australia; check current local rules before buying, growing or moving it. Root fragments and stems can establish new plants, so never dump garden waste in bushland or waterways.

• Laurel clock vine (Thunbergia laurifolia)

  Has similar blue flowers, but its leaves are generally narrower, smoother and unlobed, unlike the broad, rough, often angular leaves of blue sky vine.

• Black-eyed Susan vine (Thunbergia alata)

  A smaller, lighter climber with smaller flowers, usually orange, yellow or white, and a conspicuous dark central eye.

• King's mantle (Thunbergia erecta)

  Forms a shrub rather than a large twining vine and has much smaller leaves, with purple-blue flowers borne singly.

Thunbergia honours Swedish botanist Carl Peter Thunberg, grandiflora means large-flowered, and blue sky vine refers to the flower colour.

Propagation. Where cultivation is permitted, take softwood or semi-ripe stem cuttings during warm weather, or layer a shoot. Keep propagating material contained and dispose of unwanted roots and stems through locally approved weed-waste services.

Accepted botanical name

Thunbergia grandiflora

In the US and Canada

Introduced in Hawaii, the lower 48 states and Puerto Rico.

Native range

Assam, Bangladesh, Cambodia, China South-Central, China Southeast, East Himalaya, Hainan, Laos, Malaya, Myanmar, Nepal and Thailand.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.