An article in a 2007 edition of the 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, we tried it and it was a success, so instead of working in the cold and damp of the winter in a poly tunnel, we now 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?