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Canna

06/03/2015

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Cannas are easy to grow plants to add splashy, tropical color to the garden, although their large, showy, “flowers” aren’t really flowers and canna seeds are tough enough to be used as buckshot. 

          Red canna  
           Yellow variegated             canna foliage
Pink canna blooms
Introduction to Cannas

Look up cannas and practically any description will include the terms “bold, tropical look” and “large, banana-like leaves.” Cannas are native to the American tropics, although they are cold hardy into USDA Hardiness Zone 7b.  Cannas are a herbaceous perennial in our area, that is, they will freeze if unprotected and may die back to the ground during a cold Houston winter, but new growth will emerge each spring. They sport showy blooms in red, yellow, salmon, orange or pink and some varieties have multiple colored flowers. There are no blues, purples, or white canna flowers. The large, wide canna leaves are attractive and are sometimes grown as much for their foliage as their flowers. Leaves may be a variety of greens to purple or with multicolored variegation (including copper, pinks, reds and bronze). Cannas do best in full sun in moist soil with lots of organic matter, but often thrive on neglect as well. Native varieties can reach 8 feet in height, but most cultivars sold in nurseries or garden centers are in the more manageable 3 or 4 foot range. 

The Canna family tree

Cannas are from the order Zingiberales and the family Cannaceae. Some other related plant families are Musaceae (bananas) Heliconiaceae (bird of paradise) and Zingiberaceae (gingers). The similarities can be seen in the pictures below.

       Bird of Paradise
Banana
Ginger
Growing cannas

Cannas are easy to grow. They thrive in hot, humid Houston summers. They do best in moist, well-drained soil, but can tolerate wet or even moderately polluted boggy areas. Plant them in full sun for best flowering.

Pests such as leaf rolling caterpillars (Calpodes ethlius or Geshna cannalis) can be a problem. Best management practice is to watch for early signs of infestation, especially silk threads holding the young leaves from unfurling.  If you find the leaves are stitched closed, gently unroll the leaf and remove the caterpillars manually. Bacillus thuringiensis (Bt) or insecticidal soap can be dusted or sprayed on leaf surfaces, but be sure to apply in and around the young leaves that are still rolled up. This article from the Aggie Horticulture website explains how to control these pests in a lot more detail. 

Cannas can be grown from seed, but are easiest to propagate vegetatively from rhizomes (underground, modified plant stems). If you are starting (or storing) your own plants, be aware that rhizomes do not store well and be sure to purchase fresh ones early in the season. Most garden centers sell canna plants in 1 gallon and larger pots. Cannas will multiply fairly rapidly during a growing season to fill a space if planted 24" apart. 


Picture
canna rhizome
PictureCanna indica
Origin and History

Cannas are wildflowers from the tropics and subtropical areas of the Americas, as in Mexico, Central America and tropical South America. They were introduced to and became naturalized throughout the East Indies (Southeast Asia and surrounding areas) sometime before the 1500s, but there is some debate about whether human intervention was involved or whether some of the tough seeds made it across the ocean on their own. Then the history gets a bit tortuous. The first named Canna species, Canna indica, was introduced to Europe by the late 1500s and became very popular, especially in Victorian times. The name Canna indica means “Canna from India,” but was actually named for and brought from the West Indies (basically the areas visited by Christopher Columbus and claimed by Spain in the Caribbean). People apparently shortened “East Indies” and “West Indies” to just “Indies” and understandably the idea took hold that Cannas were from India. 


By the mid-1800s, there were supposedly over 100 species, but this had more to do with the fact that before the telephone, color photography and the internet, many competing taxonomists, collectors and institutions of learning around the world had to rely on written descriptions. Relatively slow methods of communication and publication meant that many species were discovered and named more than once. Taxonomists now consider many of these earlier named species either duplicates or cultivated hybrids and most authorities recognize either 10 or 19 species, depending on whether you agree with Dr. Maas or Dr. Tanaka…  

Scientists are still debating the number of canna species.

Dr. Nobuyuki Tanaka, a Japanese expert on the family Cannaceae, simplified things and wrote a 2001 monograph classifying 19 distinct wild species of canna based on genetic analysis and morphology. In 2008, husband and wife team Hiltje Maas-van de Kamer and Paul Maas, working in the Netherlands, further reduced that number. Their monograph identified only 10 wild canna species and grouped many of Tanaka’s Asian species into C. indica, their argument being that many Asian canna taxa were decedents of C. indica from the Americas that spread around the globe as a food crop.  


Sorting out the many types of canna got even more complicated when botanists began to develop hybridized varieties by crossing native and naturalized species from both American and Asian plants.Hybridization of wild species has gotten so complex, all ornamental canna are now called Canna x generalis which literally means “generic canna”.

Picture
Canna x generalis 'Tropicanna'



Canna flowers are a bit odd.
Petals are the showy part of many flowers, but cannas have showy, modified stamens (stamenodes).and less noticeable petals. So, the canna "flower" is really just the pollen structure. 

Cannas propagate two ways. They can propagate vegetatively, through rhizomes (modified underground stems) or sexually, through flowering and pollination. Some cannas bloom at night and are pollinated by moths and bats. Others bloom during the day and are pollinated by bees and hummingbirds. 



Indian shot

Canna seeds have supposedly been used for buckshot on occasion, hence the common name Indian shot for Canna indica. I have not been able to find an independent source to verify when and where the seeds have been used this way, although this article from the Wayne's World natural history website has an entertaining discussion about experimenting with their use in a shotgun. 

At any rate, they are very hard and durable. Canna seeds were found at a 550 year old site in Argentina in 1968 and were germinated successfully and the archaeologists' paper "Germination of achira seed (Canna sp.) approximately 550 years old" was published in the scientific journal Nature.  



Sources in no particular order:
http://www.plantdelights.com/Article/Canna-Lily
http://www.winternet.com/~chuckg/dictionary/dictionary.92.html
http://www.canna-collection.org.uk/taxonomy.html
http://waynesword.palomar.edu/pljune98.htm
http://aggie-horticulture.tamu.edu/newsletters/hortupdate/2010/may/cannas.html
http://www.eattheweeds.com/canna-confusion/
http://aggie-horticulture.tamu.edu/galveston/Gardening-Handbook/PDF-files/GH-018--canna-leafroller.pdf
http://www.aces.edu/pubs/docs/A/ANR-1315/ANR-1315.pdf