Over-wintering Cannas

A rhizome is not a bulb. In botany, a rhizome is a horizontal stem of a plant that is usually found underground, and in Canna sending out roots and shoots from its nodes. Rhizomes may also be referred to as creeping rootstalks, or rootstocks. In general, rhizomes have short internodes; they send out roots from the bottom of the nodes and new upward-growing shoots from the top of the nodes.

For Cannas, the rhizome is used by gardeners to propagate the plants by a process known as vegetative reproduction.

So how does a rhizome differ from a bulb? A bulb is an underground vertical shoot that has modified leaves (or thickened leaf bases) that are used as food storage organs by a dormant plant. A Canna is never dormant, it is growing 52 weeks of the year. That is the bit that so many get wrong when handling their Cannas over the winter.

In the northern hemisphere, in England, our Cannas are growing outdoors for 6 months and spend the remaining 6 months being abused indoors! We see books and articles telling us to dry them out, cut of the roots and then leave them in boxes of peat until the spring. Watering is hardly ever mentioned. So all the Canna will be doing is draining its energy reserves stored in the rhizome to keep life growing. If it had a bad growing summer before it may not have enough food reserves to keep going and will just give up life. We have all seen rhizomes that do that.

So, what is the best way to over-winter a Canna. It certainly is not to leave it in a pot in a garage and ignore it for 6 months. While it may still have roots, it is in soil that the ever-hungry Canna will have depleted of minerals during the summer. Although it has roots, but no food, means it is drawing on energy in the rhizome during the winter months to keep going. The least that should be done in that case is to add fertilizer to the pot, lightly water and ensure that it never dries out. It will not produce any starch to plumpen up the rhizome when it has no foliage, but it will not deplete the rhizome of its stored energy.

There is an urban myth that says that if the first leaf in the spring is bad, then the Canna has virus. A little thought and understanding would reverse that, and the wisdom should be that a good first leaf indicates great health, but while early leaves may not be good, by the time the plant is growing with roots in well-treated soil if it is not producing better and better leaves, then it possibly has virus.

We often see what happens when you buy dry rhizomes from garden centres. They are usually withered and depleted of any stored energy. They are grown over the summer and people are disappointed. However, if given TLC during that first summer and over-wintered correctly then the plant will often amaze the next year, unless it has a bad infection of virus, which is a different matter altogether. So, I always recommend waiting until the second year before passing judgement.

So whatever method you use to store your Cannas over-winter, I would recommend that you ensure that it is kept ticking over for that long winter period.

The lost six months - introduction

Here in northern Europe we plant our Cannas outside in early to mid May and we bring them back indoors again in late October, or early November. So for six months of the year our Cannas are stuck away, normally out of sight, and left to get on with it; whatever that means.

That is half the life-time of our Cannas, where we don't really understand what is going on. Cannas are not bulbs, they do not have a dormant period. They grow for 52 weeks each year and bad things that happen to our Cannas happen during that 6 month period, where they are trying to grow, but the environment does not allow it.

A few articles follow, which explore the lost six months. In the meantime, here is a picture of a Canna 'Africa' in full bloom! It is not shown for any good reason, other than it is not a well known cultivar, so the picture may be interesting.

Describe Cannas: Rhizomes

It was Dr Nobuyuki Tanaka, the Japanese taxonomist, who created a set of working measurements for Canna rhizomes, and he used them to help him categorize the wild species, resulting in his Taxonomic revision of the family Cannaceae in the New World and Asia in 2001. This revision was the start of bringing order to the chaos we had previously experienced in naming of our Canna species. The categories defined by Tanaka are:

1. thick, up to 3 cm in diameter
2. thick, up to 7 cm in diameter
3. long and thin
4. tuber-like groups
5. no rhizomes
   

To the first four specified by Tanaka, we have added the fifth category. At Claines Canna we have grown C. paniculata that did not have any rhizomatic growth, and Dale McDonnell, in Australia, has had this same experience, having inherited an old Foliage Group specimen that displays the same characteristic.

We have used this classification for some years now, and we cannot find any fault with it.

Canna News: Wot! no rhizomes?

Cannas without rhizomes.

Dry rhizomes, judge year 2

I have sometimes watched as keen gardeners plant their packaged, small dry rhizomes in early spring, they grow them on but express disappointment at the end of the season, complaining that while they had grown and flowered, there wasn’t the theatre effect that they had been led to expect from the Canna legend.

What we have to remember is that the rhizome is the sole source of energy for two separate things, not only the stem and flowers that you can see, but also a totally new rooting system. That is why small rhizomes that have dried often have a disappointing first year, any attached roots are certainly dead and useless, I always remove them altogether. The rhizome will start throwing more shoots once it has a root system to provide water and minerals, plus the required 6 hours of direct sunlight. The interaction of the rich canna foliage with light produces energy, the starch machine takes over and the starch is stored as new rhizomatic growth.

I suggest that at the end of the season, the plants should be dug up and stored with soil or compost as a clump, so that most of the root system can survive the winter as well. Then, when you have separated and planted them next season in fresh, well fertilised soil stand back quickly, while the Canna starts to perform as only Canna can!

So, my advice to anyone buying dry, packaged Canna rhizomes is to treat the first year as a growing and bulking exercise, enjoyable as that is, then pass judgement in the second season.

Canna toughies

Use herbicide in tank sprayer to tame wayward canna lilies

Oakland Tribune, Aug 23, 2003

Q. I removed a patch of canna lilies that was growing out of control. I was surprised to find that some rhizomes went down 2½ feet (95cm). My problem now is that I didn't get rid of all of them. They are starting to shoot up between the newly planted plants. The only thing I could find on the Internet to control the tubers was to burn them. Obviously, that is not an option. Any suggestion on an herbicide I can use?

A. Canna lilies can be a nuisance as they are hard to keep contained in one location. This is true of all types of rhizoming plants. All it takes is a little piece left behind to perpetuate the plant.

For your situation, Roundup is the ideal herbicide to use. The leaves and not the roots absorb Roundup, so it can be applied carefully around other plants without harming them. Protect the desirable plants with a cardboard plant shield. You could surround each plant with a shield or the unwanted canna shoots. Personally, I would isolate the unwanted shoots, apply Roundup, then move the shield to the next cluster.

I suggest using a tank sprayer to apply the herbicide instead of a hose end sprayer. It is easier to concentrate the spray in a single spot and the spray drift is minimized. You'll have to be persistent as it's a battle of attrition, but you should win it.

Some of the larger specimens can be vigorous growers

Malcolm's comments:
In case you have not read it, here is a quote from one of the funniest, tounge in cheek, articles I have encountered about Cannas:

"Ridiculously easy to grow, cannas will take root if dropped on sand, soil, asphalt, cement or slag heaps of radioactive waste. Before the arrival of the dumpster, towns had back alleys where garbage was hidden from view. Cannas grew so thick that people assumed the flowers appearance was a government beautification project. What convinced them otherwise was that the cannas throve - which they would not have had it been a government project. The truth is that these back alley orphans grew from roots discarded by gardeners who had exhausted other disposal methods like napalm, burial at sea and encasement in cement."

Canna-and-Where-It-Grows

Developing Canna agriculture

In a bid to develop an alternative source of starch for the Thai food industry, a team of biochemical technology scientists embarked on a comprehensive study of canna. The study is a collaboration between a number of higher educational institutions and scientific agencies. Leading the study team are Associate Professor Dudsadee Uttapap, associate dean for academic affairs of the Bioresource and Technology School, King Mongkut Institute of Technology Thon Buri, and Professor Dr Yasuhito Takeda from Kagoshima University’s Faculty of Agriculture in Japan. The study has mainly been funded by the Thailand Research Fund, via the Royal Golden Jubilee PhD Programme, and the National Centre for Genetic Engineering and Biotechnology (Biotec).

Dudsadee says canna starch’s outstanding attributes are its high elasticity, high viscosity, high retrogradation, and clear paste. Hence, it has very high potential to be developed as a raw material for noodles or a thickening agent in the food industry. In Vietnam, canna noodles have become more and more popular. This is because the noodles exhibit very high tensile strength. They stay firm and lose minimal solidity during cooking. Dudsadee says her team intends to develop a comprehensive knowledge of canna, especially the breeds grown in Thailand, and the feasibility of developing the canna industry in this country.

It’ll take years to complete the whole study process, she says. In her opinion, Thailand’s starch industry has very high potential to accommodate canna starch production, given that most of the required equipment and infrastructure are already in place.


But before the industry could begin investing in canna starch, comprehensive knowledge about the plant, its yield and related products have to be fully developed, she says.


Genetic attributes of edible canna must be developed as well, says Dudsasdee, so that the starch’s production costs can be lowered. Genetic development could help increase canna productivity. More importantly, canna roots have a myriad of rootlets, making current starch-processing very time consuming and costly. This is because starch producers have to pay rather high wages for the processing, she says.


Dudsadee says her team has completed only about 40 per cent of the whole study process. She identifies two key obstacles, limited funding and equipment for the slow progress of the study. So far, they have completed their study on the physical attributes of canna starch for example, the structure of the starch molecules and its pasting properties. Now she plans to explore the relationships of canna’s growing periods and different attributes of the crops from different growing periods. Information about the relationships will enable relevant agencies to guide farmers on the length of appropriate growing periods that yield the most cost-effective productivity for canna, Dudsadee says.

Summer splits

An article in this months R.H.S. "The Garden" caused me to review what I had done over the last few years and wonder if splitting Cannas can be done better. Although dividing perennials is usually a job for spring or autumn, recent findings suggest that, for some plants, summer division is better.

Firstly, although we treat Cannas as perennials, in reality they do not need rest and in their native environment they grow for 52 weeks of the year, only slowing down if temperatures go too high. In temperate climates we know that they will be destroyed by freezing temperatures and so we store them in a safe environment over the winter and early spring, until the threat of frosts is past. The risk of too high temperatures is not a problem.

Cannas do not have a true state of dormancy, they simply have an ability to survive bad weather and growing conditions in the wild, things such as fires and drought. The large store of starch in the rhizomes means they have the energy to start over again. Anyway, after subjecting them to intense distress over the winter months, we then split them and start them into growth. In the process we always have a high number of casualties, not surprising when you think that they have been in a state of extreme stress for six months, then we aggravate that by splitting them and expect them all to grow a new root system as well as top growth for us to admire.

The garden trade knows that if they don't sell the rhizomes in the spring, then they won't sell many later. So, it makes sense that the trade cleans, splits and packages over the winter for a spring sale. The trade normally sells them in packs of three, so the customer has a high chance of getting something to grow, even if the rhizomes have been subject to bad storage and display conditions.

For gardeners with an established collection of rhizomes, it may be better to plant the established, semi-dormant clumps back in the ground and then, when they are flourishing again, with a proper root system, to split them. What make me start thinking about this? For the last few years I have been trading plants with another enthusiast in July/August, and I have been splitting the rhizomes for exchange the week before his arrival. Within weeks, my own plants have recovered and thrown lots of new, fresh growth and my gardening friend has lost none of his newly potted plants.

It is noticeable that the splitting has added new zest to the plants, but it is probably just the fresh food in the new potting compost or the bone meal that I add first before replanting in the ground, and the handful of fertiliser afterwards which creates that effect, and makes them appear to outperform their companions.

Anyway, I have determined to give it a try next year, and instead of working in the cold and damp of the winter in a poly tunnel, I will leave our collection alone and just replant them in May, and then do the splitting during the summer, when I can enjoy the exercise and weather. For those not convinced, why not try splitting just one of your plants this summer and try it for yourself?