Thalia dealbata

RHS Plant Profile
powdery alligator-flag
Aquatic Herbaceous Perennial Conservatory Greenhouse

An evergreen, marginal aquatic perennial forming a clump of long-stalked, erect, narrowly ovate leaves to 40cm in length, covered with white powder, and slender stems bearing panicles of purple flowers 2cm across. Although not carnivorous as such, this plant may trap and kill small insects such as hoverflies and small bees during the pollination process.

Position

Full sun

Soil Types

Loam

Max Height

1.5-2.5 metres

Max Spread

0.5-1 metres

Size

Time to Maturity
5–10 years
Max Spread
0.5-1 metres
Max Height
1.5-2.5 metres

Growing Conditions

Loam
Moisture
Poorly–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
South–facing or West–facing or East–facing
Exposure
Sheltered
Hardiness
H2

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Marantaceae
Native to GB/Ireland
No
Foliage
Evergreen
Habit
Clump forming
Genus
Thalia can be evergreen or deciduous perennials with long-stalked, lance-shaped leaves and long stems bearing violet-purple flowers in panicles
Name Status
Correct
Plant Range
S US, Mexico

How to Grow

Cultivation

Under glass, grow in baskets of peat-free, loam-based compost in full light. Grow as a marginal aquatic in a planting basket of fertile, loamy, humus-rich soil in up to 15cm of water at the edge of a sunny pool. In colder areas it will become deciduous. See pond plants for further advice

Propagation

Propagate by seed sown at 16-21°C, in moist seed compost, when ripe or in spring. Propagate by division in spring

Suggested planting locations and garden types

  • Sub-tropical

Pruning

Remove old flowers and leaves regularly

Pests

Generally pest-free

Diseases

Generally disease-free