Plant problems

Why Are My Zizania Leaves Curling?

Q: How do I grow zizania aquatica in a UK pond?

Zizania aquatica (wild rice) can be grown in a UK garden pond, large water feature, or natural pond margin in full sun with the roots in shallow water. It is an annual grass that must be raised from fresh seed each year (the seeds lose viability very quickly and must be stored wet or cool; seed that has dried out will not germinate). Growing from seed: obtain fresh seed in autumn (the grain is shed from the plant in late summer to autumn); store the seed refrigerated in a jar of water through winter to maintain viability; sow in early spring by placing seed on the surface of a tray of wet mud or aquatic compost standing in shallow water in a warm position (above 20°C) in a greenhouse or heated propagation space; the seed germinates readily in warm, wet conditions and the young seedlings grow quickly; thin to avoid overcrowding once seedlings are established. Planting out: plant young zizania plants into aquatic compost in a planting basket (an open-sided basket designed for aquatic plants) with the surface of the basket at or below the water level, or plant directly into the mud bottom of a natural pond; the roots must be submerged in 15 to 60 cm of water throughout the growing season; do not allow the root zone to dry. Position: full sun is essential; a warm, open, south-facing pond position gives the best growth; in full sun with sufficient water depth, zizania aquatica can reach 2 m or more in height in a UK summer. The UK growing season is generally sufficient for wild rice to germinate, grow, and produce grain by September in a warm year; in a cool or short UK summer the grain production may be limited but the ornamental value of the tall, graceful summer foliage is maintained.

Q: Is zizania latifolia different from zizania aquatica?

Zizania latifolia (Manchurian wild rice, Chinese wild rice, water oats) is a perennial species of wild rice native to East Asia (China, Japan, Korea, Russia) and quite different in character from the annual North American Zizania aquatica, both botanically and in its garden use and culinary application: Plant habit: Zizania latifolia is a perennial (living for multiple years) rather than an annual; it spreads by rhizomes and can form extensive stands in wet and aquatic conditions; Zizania aquatica is a true annual, germinating from seed each year and dying after setting seed. UK hardiness: Zizania latifolia is hardier and more persistent in UK conditions than Z. aquatica; it is perennial and overwinters successfully in the margins of UK ponds; Z. aquatica must be raised from seed each year. Culinary use: the grain of Zizania aquatica (North American wild rice) is the edible wild rice of North American cuisine, a valued food grain of indigenous North American peoples and now widely sold as a premium grain ingredient; the grain of Zizania latifolia is not consumed in the same way, but the stem base of Z. latifolia that has been infected by the smut fungus Ustilago esculenta is a vegetable of great importance in Chinese and Japanese cuisine, eaten as a crunchy, mild vegetable stem and known as jiaobai (Chinese) or makomotake (Japanese); this infected, swollen, white stem base is the part of the plant consumed. Invasiveness: Zizania latifolia has become an invasive species in parts of Australia and New Zealand where it has been introduced, spreading vigorously and displacing native wetland vegetation; UK gardeners should be aware of this potential and should not dispose of the plant or its roots where it could colonise natural watercourses.

Q: What wildlife value does zizania provide in a UK pond?

Zizania aquatica (wild rice) provides significant wildlife value in a UK garden pond or wildlife water feature: Waterfowl and seed-eating birds: the ripe grain (wild rice seeds) shed from the plant in late summer and autumn is a valued food source for ducks, geese, teals, moorhens, and seed-eating birds; in North America, wild rice stands are a critical food resource for migratory waterfowl; in a UK garden pond, even a small stand of wild rice provides seeds appreciated by resident and visiting pond birds. Cover and nesting: the tall, dense stems and leaves provide cover and shelter for nesting waterfowl, wading birds, and aquatic invertebrates through the summer growing season; dragonflies and damselflies use the tall upright stems for egg-laying and the larvae of aquatic insects use the submerged stems and roots as habitat. Aquatic insects and invertebrates: the roots, stems, and leaf litter of zizania in a pond provide habitat for a range of aquatic insects, crustaceans, and other invertebrates that form the base of the freshwater food chain; a more diverse aquatic plant community (including zizania) supports a more diverse aquatic invertebrate community, which in turn supports more fish, birds, and other pond wildlife. Visual and structural value: the tall (to 2 m), upright, fresh-green stems provide vertical structure in a pond planting, contrasting with lower-growing aquatic plants and providing a backdrop for smaller pond margin plants; the open, airy flower panicles of wild rice are also ornamentally attractive in their own right. Comparison with common native pond plants: zizania is not native to the UK and may be considered an introduced species in a wildlife garden context; native alternatives for tall, structurally similar pond plants include Glyceria maxima (reed sweet grass), Sparganium erectum (branched bur-reed), and Typha latifolia (common bulrush).

Zizania aquatica (wild rice) is a tall, annual aquatic grass grown in UK garden ponds for its dramatic fresh-green summer foliage reaching 2 m or more, its ornamental grain panicles in late summer, and its value to pond wildlife. A true aquatic that needs its roots permanently submerged. Leaves curl and yellow from water level dropping, insufficient light, or the normal annual die-back in autumn.

Insufficient water depth or drying out

A true aquatic, zizania must grow with its roots submerged in shallow water (15 to 90 cm deep) throughout the growing season. If the water level drops and the root zone dries out, the long, broad leaves curl from the margins and the leaf tips brown and die back very rapidly; zizania is much more sensitive to drying out than most bog garden plants and shows visible leaf curl within days. Seasonal pond level fluctuations in a dry UK summer are the most common cause of leaf curl in container-grown plants.

What to do

Ensure the root zone remains submerged throughout the growing season; top up the pond in dry spells to maintain a minimum water depth of 15 to 30 cm over the planting basket. In a container water feature, check water levels daily in hot weather; the combination of transpiration from the tall, broad leaves and summer evaporation can drop a small container water feature significantly in a warm day. Maintain the planting basket at a submerged depth; do not allow it to be lifted out of the water by water level drops.

Insufficient light

Wild rice is a sun-loving aquatic grass of open, exposed, shallow freshwater habitats; in a shaded pond, the plant becomes weaker, narrower, paler, and more prone to yellowing and curling. At least six hours of direct sun per day is needed; a south-facing or open pond position in full sun gives the best growth and the most dramatic 2 m stems in a UK summer. Overhanging trees or structures shading the pond are the most common cause of light deficiency.

What to do

Grow in the most open, fully sunny pond or water feature position available; avoid planting in a pond shaded by trees, walls, or buildings. If the pond is partially shaded by an overhanging tree, position the zizania in the sunniest part of the pond rather than under the shaded area. In a small container water feature, move to the sunniest available outdoor position for the growing season.

Autumn annual die-back

Zizania aquatica is an annual; as temperatures cool in September and October after seed set, the above-ground growth yellows, curls, and dies back as part of the normal annual lifecycle. This seasonal die-back is not a treatable cultural problem. The grain shed by the dying plants in autumn provides food for pond wildlife and the seed persists in the wet pond sediment to germinate again next spring in suitable conditions.

What to do

Allow the plant to complete its full annual cycle including grain ripening and seed shed before removing the dead stems; the shed grain provides wildlife value and may germinate in the pond sediment the following spring. In a managed wildlife pond, no intervention is needed; in a formal pond where the dead material is undesirable, remove dead stems after seed shed in October or November. Retain the planting basket in the pond for any self-seeded plants that may germinate from shed grain the following spring.

Frequently asked questions

Why are my zizania leaves curling?

Zizania leaves curl most commonly because of insufficient water depth or drying out (true aquatic; roots must be permanently submerged 15 to 90 cm deep; water level drops in dry UK summers cause rapid leaf curl; top up the pond in dry spells; maintain planting basket fully submerged), insufficient light (sun-loving aquatic of open, exposed habitats; six hours direct sun minimum; shaded pond causes weak, pale, narrow, curling leaves; position in the sunniest part of the pond), or autumn annual die-back (normal end of the annual lifecycle; above-ground growth yellows and dies after seed set in September to October; allow grain to shed for wildlife value before removing dead stems). Submerged roots in a sunny pond are the two essential requirements.

How do I grow zizania aquatica in a UK pond?

True aquatic; roots must be submerged 15 to 60 cm deep throughout the growing season. Raise from fresh seed: store seed refrigerated in a jar of water through winter; sow in early spring in wet mud or aquatic compost in a warm greenhouse (above 20°C); seedlings grow quickly in warm wet conditions. Plant young plants into aquatic compost in a planting basket at or below the water line; or direct into natural pond mud. Full sun in a warm, open, south-facing pond position; can reach 2 m or more in height in a warm UK summer. Annual; must be raised from seed each year; shed grain may self-seed in the pond sediment.

Is zizania latifolia different from zizania aquatica?

Yes; Z. latifolia (Manchurian wild rice) is a perennial native to East Asia (China, Japan, Korea) that spreads by rhizomes; Z. aquatica is a North American annual raised from seed each year. Z. latifolia is hardier and persists in UK pond margins without annual reseeding. Culinary difference: Z. aquatica grain is the edible North American wild rice of cuisine; Z. latifolia grain is not consumed, but the swollen stem base infected by the smut fungus Ustilago esculenta is jiaobai (Chinese) or makomotake (Japanese), a valued crunchy vegetable. Z. latifolia has become invasive in parts of Australia and New Zealand; do not dispose of roots where it could colonise natural watercourses.

What wildlife value does zizania provide in a UK pond?

Waterfowl and birds: ripe grain (shed late summer to autumn) valued by ducks, geese, teals, moorhens, and seed-eating pond birds. Cover and nesting: tall dense stems provide shelter for nesting waterfowl and aquatic invertebrates; dragonflies and damselflies use upright stems for egg-laying. Aquatic invertebrates: roots, stems, and leaf litter support a range of insects, crustaceans, and invertebrates forming the freshwater food chain base. Structural: tall (to 2 m) upright fresh-green stems provide vertical contrast in a pond planting. Native alternatives (for wildlife gardens): Glyceria maxima (reed sweet grass), Sparganium erectum (branched bur-reed), Typha latifolia (common bulrush).