TL;DR | Alligator flag (Thalia dealbata) is an exotic-looking marsh plant with purple flower clusters and decorative blue-green foliage. This graceful species is hardy and perfect for pond edges and marsh zones. This species can grow up to 150 cm tall and usually flowers between July and September. With its sturdy structure and striking appearance, Thalia dealbata is a low-maintenance plant that immediately attracts attention in natural ponds. Order Thalia dealbata easily via our partner Vijvermeester.co.uk
Thalia dealbata, better known as Alligator flag, is a striking aquatic plant native to the swamps of the southeastern United States. This plant impresses with its stately leaves, striking flowers and graceful growth habit. Although its exotic appearance suggests otherwise, Thalia dealbata is surprisingly hardy and well suited to the Dutch climate. Suitable for use along pond edges, in wet areas or as a free-standing plant in a spacious water trough or planter.
Order easily via our partner: Thalia dealbata ordering from Pond Master.
Thalia dealbata belongs to the family Marantaceae. The plant grows from a rhizome and develops firm, blue-green leaves resembling fins. Its upright petioles can grow up to 150 cm tall, adding an architectural element to the pond.
In the summer months, the striking flowers appear on long stems. The inflorescence consists of small purple flowers arranged together in dense spikes. The compact flower clusters stand out beautifully against the plant's robust, blue-green foliage. Flowering usually occurs between July and September.
The flowers of Thalia dealbata have a special pollination mechanism in which small insects are sometimes temporarily trapped inside the flower to promote pollination.
Key features at a glance:
Thalia dealbata does best in a sunny location with wet, nutrient-rich soil. It prefers to grow in the riparian zone of ponds, where the roots are in the water but the leaves protrude above the surface. The ideal planting depth is between 5 to 25 centimetres below the water surface. The Alligator flag also works well in a large tub or plant basket.
When planting, it is important to provide a good soil layer at least 10 cm thick. Suitable materials include pond soil, clay, loam or pond substrate. Preferably use a pond basket with cover material such as lava pebbles to keep the plant in place.
Although Thalia dealbata has an exotic look, the plant requires little maintenance. Once autumn arrives, the visible parts of the plant disappear naturally. These can be cut off to prevent them from ending up in the water and adversely affecting water quality.
The plant overwinters via its rhizome and re-sprouts in spring. Fertilisation is usually not necessary. In nutrient-rich ponds, the plant draws sufficient nutrients from its surroundings. Preferably do not use fertiliser near open pond water to prevent excessive algae formation.
Thalia dealbata is an excellent choice for the ecological pond edge. With its height and robust stems, the plant offers structure and visual layering. Its broad leaf cover shields the water from direct sunlight, lowering the temperature and inhibiting algae growth. The flowers attract various insects, including butterflies and bees, contributing to biodiversity around the pond. In addition, the plant provides hiding places for frogs and other pond inhabitants.
Arrowweed fits perfectly into ponds designed with ecology in mind and a natural look. Preferably place the plant in a pond basket or directly in the bottom in a place where the leaves can protrude well above the water.
Thanks to its graceful appearance and long flowering period, Arrowweed is also an attractive addition in ornamental ponds with marsh zones or riparian edges.
Yes, this plant is completely hardy, if properly rooted before the frost period.
Provide nutrient-rich, wet soil and plenty of sunlight.
Only in autumn to remove dead parts.
Thalia dealbata can be ordered through our sales partner Vijvermeester.nl.
© 2025 Dutch Water Tech. All rights reserved.
English (UK) 
Nederlands 
Deutsch 
Français