PlantFiles: American Water Willow Dianthera americana
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Height: 24-36 in. (60-90 cm) 36-48 in. (90-120 cm)
Spacing: 18-24 in. (45-60 cm)
Hardiness: USDA Zone 3a: to -39.9 °C (-40 °F) USDA Zone 3b: to -37.2 °C (-35 °F) USDA Zone 4a: to -34.4 °C (-30 °F) USDA Zone 4b: to -31.6 °C (-25 °F) USDA Zone 5a: to -28.8 °C (-20 °F) USDA Zone 5b: to -26.1 °C (-15 °F) USDA Zone 6a: to -23.3 °C (-10 °F) USDA Zone 6b: to -20.5 °C (-5 °F) USDA Zone 7a: to -17.7 °C (0 °F) USDA Zone 7b: to -14.9 °C (5 °F) USDA Zone 8a: to -12.2 °C (10 °F) USDA Zone 8b: to -9.4 °C (15 °F) USDA Zone 9a: to -6.6 °C (20 °F) USDA Zone 9b: to -3.8 °C (25 °F) USDA Zone 10a: to -1.1 °C (30 °F) USDA Zone 10b: to 1.7 °C (35 °F)
On Jan 13, 2010, larrylb from meadville,pa United States wrote:
Dianthera americana (water willow) is quite ubiquitous along French creek in NW PA... This colony-forming, interminable plant can be seen in the the shallow waters and along the sandy islands from June to October... It is not affected by the rising water, which floods the banks and islands periodically in spring and summer or by the ice that covers the entire creek most of the winter... It's quite contrasting, growing among the Acorus calamus (Sweet flag)... Both 'Peterson's Field guide' and the 'National Audubon Society field guide' list it as Justicia americana...
On May 20, 2009, Delphine61 from Mobile, AL wrote:
We have this in a container in our pond in Mobile, AL and after several years it's spread itself out among the rocks and is even reaching the "bank." Blooms all through May. Our landscaper seemed amused that we'd paid money at the Ponde Shoppe for a weed, but I love the pretty little flowers.
On May 29, 2008, pyromomma from Columbia, SC (Zone 7b) wrote:
I have not grown this, but it is wild and prolific here in SC.
Here is the conversation that I had with the Clemson herbologist when asked to identify the plant:
" J. americana is also called Dianthera americana, often called 'water-willow'. It is in the family Acanthaceae. This is a nice native plant, always found in shallow water and sandy gravel at the margins of rivers or permanent streams.
I have had some luck growing the Justicia in a container set in a pool, so I think it is worth a try. Water circulation should not be needed. I'm not sure if it is generally sold as a waterplant, but a quick check on the internet should help. I love the flowers- they remind me of small orchids. They do like sun, by the way. They may not flower in shade. Also, they like shallow water - I would put them in a pot in water that comes up to the top of the pot, maybe 6 " or so. Or, they can be grown without a pot in a more natural setting. They will stand some freezing, and I think heat is not big problem. A nice one to try."