Monday, 19 November 2007

The Effects of Drought on Cannas

The Canna blooming season has well and truly arrived in the southern hemisphere. At least it has where Cannas are receiving any water. The southern half of Australia is still in the grip of an eleven year drought, the worst in our history and it is only recently that the northern tropical and subtropical climes have started to have their summer rains after several below average rainfall seasons.

Here in the southern half of the country most towns are on severe garden watering restrictions after the winter and spring rains failed completely. Farmers dependent on summer irrigation to milk cows, grow crops and produce fruit, have had their "guaranteed" irrigation water allocations slashed. Normally they have 100% allocation plus another 100% excess water sales. Ensuring an effective buffer against our sweltering, dry summers. Most will only receive 10% allocation, no excess water sales and some areas will have zero allocations apart from stock and domestic supplies which will at least water their livestock. The stock will have to be hand fed very expensive grain and hay in place of lush pastures.

Last summer my Canna collection had to subsist on recycled water from shower and washing machine. We were not allowed to use any clean water outside the house. This spring, restrictions have, at the moment, been eased a little to allow watering of garden beds (no lawns allowed) twice weekly for one hour per day. This can only be done using a hand held hose. In a garden so crammed with plants as mine, this means that each bed is lucky if it receives a splash of water once every two weeks. Although it is the last month of spring, the temperatures are soaring and more like those of mid summer.

How are the cannas faring? Surprisingly they are still alive. Last season the severe lack of water saw them only reaching about 30% of their normal height. Prolonged flowering was much reduced due to lack of increase of the rhizomes.

The foliage this season is showing signs of stress although it was okay last season apart from the leaves being smaller. Foliage on those 100 or so overwintered in the ground at our old property is better than that of those living in luxury in their new environment. These 300 cultivars were moved to our new property and planted in early winter. The first leaves of these are also showing horrible streaked and blotched foliage but the most recent leaves are unfurling fresh and clean. Flowers do not seem to be affected and the first blooms look wonderful. A plentiful water supply was the primary motivation for the move and cannas growing on the new property have received a thorough weekly soaking. They went into stockbeds lavishly enriched with well rotted cow manure. Consequently they are at least two months ahead in development compared with the poor old 100 still languishing in their old home. These later are looking very parched and only just unfurling their first and second leaves, but the streaking and blotching is nowhere near as obvious as those already transferred. The sooner we have them all settled into their new stockbeds with lots of water available and some of the most productive soils in Australia to dine upon, the better. This reinforces my belief that the most optimum time to divide and move cannas is when they are in full growth.

The delay in completing the transfers of the last 100 cultivars before the growing season commenced has, in part, been due to the fact that these particular rhizomes had not been lifted for three years. Consequently a lot of them had "walked" away from their name stakes and cuddled up amidst neighbouring cultivars. Until they showed some leaves, it was very difficult to find who had walked where. Indeed, it was difficult to determine even if a cultivar had survived the cumulative abuse of the past few years until they poked their noses up out of the ground. I grow my cannas in mixed plots with other shrubs, grasses and perennials and was loathe to plow up whole beds looking for them. We still have to put the house up for sale and a backyard of fallow dirt is not a good look. Remaining perennials should soon cover the bare spots where cannas are removed providing we don't completely devastate them. As soon as we have a cool spell these laggards will join the rest of the collection. I can't face lifting and bagging cannas and then replanting in temperature hovering around 38 degrees C. The cannas will not mind the heat, but I will.

The most noticeable effect on the cannas from such draconian treatment is that the amount of rhizomes have dwindled alarmingly. Where once there was a clump one metre in diameter containing a potential forty or fifty divisions, there is now only one or two skinny, undernourished rhizomes left alive. This is not the case for all, but the majority have dwindled. Surprisingly we have only lost two cultivars completely. Apparently unaffected by the drought are 'Pennsylvania' and ancient 'Guttermanii'. No two cannas could be more unalike. C. x 'Pennsylvania' is a big, red Wintzer raised triploid and C x 'Guttermanii' (syn. 'Sparks' in USA) is one of the very early Année French hybrids circa late 1840s.

C. x 'Pennsylvania' (left).

C x 'Guttermanii' (below)

The most devastated canna in the collection was one obtained from the old Bendigo Canna Collection. It long ago lost its identity and is either another of the very early French hybrids or a species Canna. I nicknamed it "The Bendigo Banana" because of its close resemblance to a Musa. It has never flowered for me and cannot be identified until it does. The foliage is a pale, lettuce green, poised on long, arching pedicels. The long leaves, have prominent, close veins, undulate margins and fold downwards. In windy weather these split and look just like Musa foliage. One small clump of this has completely died. The other much larger clump is reduced to just two small knobs of rhizome. Fortunately it is bouncing away in its new home but for a few weeks I thought it was caput. No doubt that this lack of rhizome stamina is due to the peculiar rhizomes the plant produces. It does not tiller like other cannas. Each leaf stalk arises from an individual small conical knob. I believe this to be the only plant left in the world of this cultivar. Supposing of course that it proves to be an early hybrid and not a species. On the right, you can see the peculiar rhizomes.


  1. Dale,

    There are three possibilities, all dependant on the flower colour. And it won't flower! OK.

    The possibilities are:

    Canna musaefolia, a 'lost' species without rhizomes. Flowers small, orange-yellow.

    Canna 'Musæfolia Minima', a cultivar with small orange brown flowers.

    Canna 'Musæfolia Perfecta', a cultivar with small yellow flowers.

    You have a totally unique and special specimen under your control. Please treat it well, we can only dream of growing it as well!


  2. Thanks for those suggestions Malcolm. I'm hoping that my old mystery might flower in the new environment. The season at the new property is about six weeks longer than Bendigo. As soon as it bulks up again I will pop a piece into a huge pot and bring it into the poly house for the winter away from our light frosts. This will keep it ticking over and ready to take off next spring.

    Seeing the pseudo rhizomes of this Canna, I can now well believe that the rhizome descriptions from 1879 Robinson's, "The Subtropical Garden", may not be as fanciful as we have been thinking.

    I do treasure this cultivar and have been holding my breath waiting to see if any of the shrivelled knobs survived. Even my vegie garden obsessed husband is anxiously watch the progress of the Bendigo Banana. The surviving knobs are now up 30 cms high thank heavens. I even potted a piece and popped it amongst my water hungry potted Brugmansia collection. That piece has not yet shown any signs of life.

    It was growing for the past two seasons in a corner with 'Stuttgart' and 'Erebus' who thrived on the scant water rations. I had assumed that the Bendigo Banana was happy too. After all, Erebus is supposed to love growing actually in the water. I have had to dispose of several wheelbarrows of excess rhizomes from the greedy neighbours 'Stuttgart' and co., who went right on increasing madly despite the drought.

  3. Glad to report that the Bendigo Banana Canna is thriving in its new home and beginning to increase rapidly.