Thalia dealbata - Powdery Alligator Flag, Pond Marginal Plant
Thalia dealbata - Powdery Alligator Flag, Pond Marginal Plant
£10.72
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Planting Time
Flowering Time
Thalia dealbata, known as powdery alligator flag or water canna, is a tall marginal plant with long-stalked, blue-green leaves dusted with white powder. From June to September it carries sprays of purple flowers on tall, slender, arching stems.
Powdery alligator flag at a glance
| Botanical name | Thalia dealbata |
|---|---|
| Common name | Powdery alligator flag, water canna |
| Plant type | Tall, clump-forming perennial; dies back in UK winters |
| Height and spread | About 1.5–2 m tall (RHS: up to 2.5 m), 50–100 cm wide |
| Flowers | Purple-violet, in sprays on tall arching stems, June to September |
| Position | Full sun, sheltered |
| Soil | Fertile loam in a planting basket |
| Pond depth | 0–15 cm of water over the crown |
| Hardiness | RHS H2 – tender; needs frost-free winter protection (1 to 5°C) |
| Native to | South-eastern USA (not UK native) |
Is Thalia dealbata hardy in the UK?
Not reliably. The RHS rates it H2, which means it needs protection from frost. UK aquatic nurseries sell it as an outdoor marginal and advise moving it into deeper water for winter so the roots do not freeze. In cold gardens, keep it somewhere frost-free over winter.
Where to plant it
- A sunny, sheltered pond shelf with up to 15 cm of water over the crown
- The back of a larger pond, where its height can be seen
- A planting basket of fertile loam
Is it good for wildlife?
Insects visit the flowers, but the RHS notes that the flowers can trap and kill small insects such as hoverflies and small bees while they feed.
How big does it grow?
Large. The RHS gives 1.5–2.5 m, and Wetland Plants says it can take up to 5 years to reach full height, so allow plenty of room.
Which size should I buy?
Bare-root plants (7 cm, 9 cm, 1 litre and 3 litre) arrive without a pot or compost and are the most economical way to plant a group. Potted plants (9 cm, 1 litre and 3 litre) arrive growing in our peat-free compost and give a faster display. Packs of 3 come in 7 cm, 9 cm, 1 litre and 3 litre bare-root sizes and cost less per plant. The 2x Pot & Compost option is two plants supplied with pots and compost.
Pond depth: 0 - 15cm
Light: Full sun
Hardiness: Hardy
Height and spread: 120cm+ tall, 50 - 100cm wide
Planting and flowering months are shown in the calendar under the photos.
Bare root (7 cm, 9 cm, 1 litre, 3 litre): plants sent without a pot or compost, ready to plant straight away. The most economical way to plant a group.
Potted (9 cm, 1 litre, 3 litre): plants growing in our recycled, peat-free compost made in Lincolnshire. Larger sizes give a faster display.
Pack of 3 (7 cm bare-root, 9 cm bare-root, 1 litre bare-root, 3 litre bare-root): three plants of the chosen size at a lower price per plant.
2x Pot & Compost: two plants supplied with pots and compost.
Sizes shown with a line through them are currently unavailable.
At Lincs Plants, we strive to provide fast and reliable shipping to ensure your plants arrive in perfect condition. We offer 1-3 day shipping through a variety of dispatch methods to suit your needs.
Processing Time:
Orders are processed within 1 - 3 business day after payment confirmation. Orders placed on weekends or public holidays will be processed the next business day.
Shipping Methods:
- Standard Shipping (1-3 days)
- Express Shipping (1-2 days)
Should you have any questions or concerns about your shipment, feel free to contact us.
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