Dr. McDonald received a BS and MS in Floriculture and a Ph.D. in Horticulture. After being educated beyond his intelligence, he is now a Clinical Assistant Professor of Ornamental Horticulture. His area of research is selecting and developing landscape plants for sustainable landscapes.

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A Canna Renaissance
by Garry McDonald       #New Trends   #Ornamentals   #Plant Profile

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cannova ‘Bronze Scarlet’ has scarlet red flowers and bronze foliage.

Working on a university campus, I can’t help but notice the changing whims of fashion. Lately, the trend among young men is khaki walking shorts, polo shirts, and white crew socks and white sneakers: exactly what we wore on campus in the early 1980s. Like clothes, plants come into and fall out of fashion. Re-discovering old garden plants is usually the result of breeding improved cultivars or someone taking a fresh look at how plants can be used in the landscape. One such plant is canna.

Canna is certainly not a new plant, being very popular in Victorian gardens and into the 20th-century. The original garden plant, Canna indica, commonly called Indian shot because of the small hard round black seeds resembling shotgun pellets, is native to many areas of the Americas, from South America to Mexico, and the West Indies. This species, one of about 20 naturally occurring, is now naturalized over many parts of the world, including the Gulf Coast of the United States, especially along perennial streams and rivers. Modern cannas are hybrids between many species and were once lumped together as Canna x generalis, although this species name is now considered invalid among the taxonomists. Because of the complex hybridization over the decades, instead of a specific species, canna are placed in cultivated plant groups with similar morphological characteristics, such as those with large colorful foliage or those with showy flowers. Other groups are grouped by geographical origin or by use, including those used as food for humans and livestock. An interesting fact is that canna is an excellent plant to use in bioremediation, especially in constructed wetlands, to filter out runoff sediments, excess nutrients, and heavy metal contaminants.


Once a signature plant of formal Victorian plantings, canna has experienced a revival among gardeners.
 

I don’t suppose there is any one reason for canna falling out of favor over the years, but several factors probably came into play. Canna was a mainstay of the intensely cultivated and managed Victorian and Edwardian gardens of the late 19th and early 20th century. Two world wars, a worldwide economic depression, and social change ended these types of gardens. Home architecture styles changed along with taste in plants and gardening. Smaller gardens and the desire for low-maintenance landscapes also influenced plant choices. Competition from the leisure industry and modern technology further affected garden tastes during the late 20th century. New pests were also contributing factors, especially viruses, which infected canna stocks, reducing plant vigor and flowering. Since propagation was once limited to divisions of the rhizomes, the number of plants that could be propagated were few and virus-infected plants could not be shipped or sold.

Cannova ‘Lemon’ has creamy yellow flowers and is ideal for mixed containers.

The advent of virus-indexed plants and micropropagation through tissue culture eliminated many roadblocks to growing modern-day canna and recent breeding work has re-invented an old plant for new gardens. Last season we were able to trial a new series of canna called Cannova, which are F1 hybrids bred specifically for mixed container plantings, although they can also be used in traditional flowerbeds. These new cannas range from a creamy yellow to scarlet red with both green and bronze leaves. In containers, they adjust to a smaller pot size with smaller foliage but with heavy flower power that readily rebloom. In the ground, they grow taller and flower just as well, although under our conditions they didn’t grow as large as traditional varieties, which for us was a good thing. Based on one year’s observations, they performed better than the Sunburst series, which was one of the first to be bred for small stature. To be safe, we dug up a set of plants to overwinter in a protected spot while the remainder stayed in the ground to test cold-hardiness. With several nights down around 0 F, we’ll see what comes back in May. I always like to test plants for a couple of seasons for landscape performance so the jury is still out.

The cultivar that kicked off a renewed interest in canna was probably ‘Pretoria’ also known as ‘Bengal Tiger’, which is a better descriptor since the variegated foliage is tiger-striped. The flowers, while orange, were not much to text home about, the plant being grown primarily for the foliage. Another cultivar that has great foliage but less-than-spectacular flowering is ‘Bird of Paradise’. This canna has long strap-like green leaves with a flush of subtle purple striping. The flowers are a soft pink and small. Since ‘Bird of Paradise’ grows taller than wide, it adds structure and bulk to a perennial bed. Canna musifolia is a species-type with large banana-like foliage that is green with purplish red stripes and can reach 10 feet tall, so maybe not the best plant for a small garden, but definitely makes a statement. As mentioned above, the Sunburst series come in a range of colors and only grow to a height of 2 feet, making them ideal for containers and smaller landscapes.


The bold foliage of bronze-leafed cannas makes a statement in the garden even without flowers.
 

Cannova ‘Rose’ has bright rose flowers and green foliage.

Cannas are easy to grow throughout the South and thrive, even demand, full sun. The only exception is the cultivar ‘Stuttgart’, named for the town in Germany, not Arkansas, which has dramatic foliage with cream to white stripes. In the South, ‘Stuttgart’ will need heavy shade to prevent the foliage from burning in the summer. Canna adapts to any average garden soil and enjoys, moist rich soils and can be grown in wet areas, including along the margins of ponds or wetlands. I’ve even seen them planted in tubs and sunk in water gardens. Cold hardiness varies by cultivar, but most are reliable to USDA Zone 7, although we get away growing them in Zone 6b most years. Mulching heavily after they die back to the ground in fall will help them overwinter. If in doubt, they are easily dug in the fall and can be stored in a cool, dark location in a tray containing dry peat moss or wood shavings. Divide if necessary and replant after the soil has warmed in the spring. Cannas respond to grooming, such as removing spent flower stalks and old tatty foliage and some are even self-cleaning. If grown in containers, grower recommendations are to fertilizer the cannas with a liquid feed every couple of weeks during the summer and water well. Cannas are affected by few diseases and the two main pests are the canna leaf roller, which can devour entire leaves, and the lesser canna leaf roller, which stitches the young leaves before they unfurl and munch in the rolled up leaf causing the leaf to collapse. These cause more of an aesthetic problem rather than killing the plant. Bacillus thuringiensis (Bt) applied at the first sign of damage usually does a good job of controlling them. If the infestation is too bad, I’ve been known to cut the whole planting back to the ground and let the canna start over. It sets them back a bit, but they don’t seem to mind. It is also recommended to remove all the canna detritus in the fall to eliminate overwintering habitat for the pests. The only other serious pests, in a bad year, are Japanese beetles, which feed on the flowers. I usually employ a seek-and-destroy (stomp) strategy of control.

 

A version of this article appeared in an April 2018 print edition of State-by-State Gardening.
Photography courtesy of Garry McDonald.

 

Posted: 04/02/18   RSS | Print

 

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