Grow and Care for Alligator Flag

Grow alligator flag in standing water and full sun. Thalia is also sold as water canna. It is not a canna lily.

Keep it in standing water and full sun

Alligator flag wants wet mud or shallow water. Full sun is the usual pond-edge home, and part shade still works when the mud never dries. [1] powdery alligator-flag uses that wet as powdery blue-green leaves and a violet panicle. red-stemmed alligator-flag uses the same wet, with red stalks and no powdery coat. Both plants share the same need for water. Neither one is a dry-bed canna or a windowsill houseplant.

Plant the rhizome in a pond pot, with water over the crown

Plant in spring from a potted plant or a rooted division. Set the rhizome in heavy loam in a five- to twenty-gallon pond pot, with the buds facing up. Set that pot so water covers the crown, usually several inches to about 18 inches in the growing season. [2] Leaves should stand above the surface.

1. Plant in spring, once the water will stay up and new shoots are starting.
2. Set the rhizome in heavy loam in a five- to twenty-gallon pond pot, with the buds facing up, not buried in a deep hole.
3. Set that pot so water covers the crown. Several inches to about 18 inches is enough in the growing season; do not drop it off a deep shelf where the leaves stay underwater.
4. Add a few rocks in the pot so wind does not tip a tall clump.
5. Bag extras. Do not toss them into a lake, ditch, or storm drain.

Split a crowded clump in spring

Most gardeners start a new patch from a rooted piece, not from seed. Lift a crowded clump in spring while the mud is wet, keep a bud and some roots on each piece, and replant at once in wet mud or a fresh pot.

1. Lift a crowded clump in spring while the mud is wet and workable.
2. Pull or cut a piece that has roots and at least one bud.
3. Replant at once in wet mud or a fresh pot, and keep it wet while it takes.

After frost, cut it back and keep the rhizome from freezing

The tops brown after frost, and new leaves come from the rhizomes in spring if the crown stayed wet and did not freeze. Cut the dead stems after frost, then sink the pot so about 18 to 24 inches of water covers the crown, or move it to a bright, frost-free room and keep the soil wet. [3] Red-stemmed alligator flag is less hardy than powdery alligator-flag, so bring that pot inside before a hard freeze.

1. Cut the dead stems after frost browns the leaves.
2. Sink the pot so about 18 to 24 inches of water covers the crown, or move it to a bright, frost-free room and keep the soil wet.
3. If it is growing in wet ground, cut the tops and mulch heavily so the rhizome does not freeze.
4. Bring a red-stemmed plant indoors before a hard freeze, and keep the soil wet.

Not a canna lily — and not a prayer plant or a daffodil named Thalia

A tag that says water canna or hardy canna is often alligator flag, not a canna lily. Canna has large red, orange, or yellow flowers, and the rhizomes rot in standing water. Alligator flag has small violet flowers and wants wet mud. See How to Grow Canna Lilies.

Prayer plant is Maranta, a houseplant in the same family that wants a damp indoor mix, not a pond — see How to Grow Prayer Plant. A spring-bulb tag that says Thalia is Narcissus, a daffodil — see How to Grow Daffodils. Pickerelweed is shorter, with heart-shaped leaves and a denser flower spike. Powdery alligator-flag has a white coat on the leaves. Red-stemmed alligator flag does not. [4]

Set alligator flag in standing water or wet mud, plant the rhizome in a pond pot with water over the crown, and cut the dead stems after frost so the rhizome does not freeze.