The bananas, such as Musa basjoo, have given me the most fun. Anything which is reduced to frost- blackened stumps and which magically starts to push out new green leaves almost as you watch can’t fail to fascinate! First out of the starting blocks is Musa basjoo that easily reached 4m. with me here in its second year. A year later in 2006, record temperatures and heavy rain in August pushed this to nearer 5m. In accordance with what I have read in the literature and on some internet postings, Musa sikkimensis seems to need higher temperatures before it gets going. My plant was virtually indistinguishable from Musa basjoo by the end of the summer although new leaves do have a dark red sheen on their undersides. My plant was raised from seed and if I do ever have to plant a new specimen, I would take the trouble to buy the variety that has clearly visible banding on the leaves. If all this is not important to you, stick with Musa basjoo. A final point, don’t plant a banana where its leaves will get shredded by strong winds.
Water, food and sun
The property of “explosive growth” in bananas and some other sub-tropical plants depends on providing ideal growing conditions i.e. the right amount of food, water and adequate temperature along with plenty of sun. However, some bananas such as Musa itinerans come from shady woodlands in their native habitats in Yunan. (This particular plant is potentially the tallest banana but I understand that its overwintering properties are difficult and this was confirmed when it failed to resurrect after a winter which gave no problems for either Musa basjoo or Musa sikkimensis.) Food comes in the form of a good mulch of well-rotted manure, courtesy of my neighbour and his cows, that I supplement with general-purpose fertiliser. In practise, the manure accounted for about 95% plus of the food and we have been rewarded with massive, healthy leaves but no flowers or fruit until 2009. However, more on this topic shortly. The tropical border is on just about the highest and driest bit of the garden so I cater for sufficient moisture by creating subterranean ponds under both bananas and gunnera. This amounts to putting saucer-shaped agricultural foil about 1 to 1.5m below the surface under the central part of the plants. Roots then find their way in and around this. In the long, dry periods a few minutes with the hosepipe are all that are needed to replenish stores for a week or two.
In the winter, I put down a good layer of dry leaves with a roof of bubble plastic which serves the dual purpose of keeping frost away from the roots and the base of the stems and stopping my “ponds” from building up water which might conceivably rot the roots of the bananas. A combination of too much water at a time when the plant is not growing is a potently fatal combination for many plants, especially the more tender ones. Banana stems are effectively columns of water held in place by vegetative cells that rupture the moment the water freezes.
In Spring new growth comes from the centre of the old shoots. If you carefully cut back the stem in spring to the point where it is green in the centre, this is far enough.
The temperature in spring has noteworthy effects on tempting bananas into growth. The spring of 2006 was especially long and cold and M. basjoo started into growth and developed slowly from green stems about 80cm high which I had brought through the winter. With Musa sikkimensis a green point seemed to be starting to push out from the centre of 3 seemingly healthy green stems and on a rare warm, sunny day. However, this start into growth simply stagnated and the stems basically degraded over several weeks. They did not go black and mushy which would be symptomatic of frost damage and rotting but just seemed to die such that playing a hosepipe on them easily peeled off the stem steadily lower and lower with no sign of life. It is difficult to describe but suffice it to say that Musa basjoo stems remained solid and robust under similar treatments. Musa sikkimensis simply came strongly from new basal shoots once the weather really warmed up. I have shared my observations on this behaviour with other friends, notably Hans Prins who were not surprised by Musa sikkimensis’s reluctance to grow from an over wintered stem. As global warming tempts more gardeners to experiment with exotics, particularly with decorative bananas, a comparative study of the effect of spring temperatures would arouse widespread interest.
Flowers, fruit and fertilizer
The winter of 2008/2009 in The Netherlands was the first in a number of years which approached something one could describe as having prolonged low temperatures – after Christmas there was a protracted cold spell during which we experienced -8 deg C and then spring was preceded by a cold spell. I took the protecting dry leaves from around our Musa basjoo clump on 1 April which is later than I had ever done in previous years. It commenced growth much later than ever before and to the extent that I was wondering if the long, cold spell had almost killed a lot of it. However, once it started into growth, it soon put out its characteristically massive leaves from the ~1m high stumps which soon developed into sturdy trunks up to 3m high with leaves to ~4m and more. Business as usual, or so I thought. I was walking round the garden with visitors right at the end of September when I noticed that a flower was forming on one of the stems. It wasn’t immediately very visually spectacular because it couldn’t have been positioned in a much more difficult place for it to be viewed but the accompanying photo gives an idea of how it appeared to a passer-by. I delayed cutting back the stems of the banana until the first frost was certain to let the fruiting process progress as far as possible. (It is noteworthy that November 2009 was the mildest on record here with temperatures often well over 10 deg C even at the end of the month.) In the first week of December, a high pressure area moved in such a way as to pull cold north-easterly winds over us and frost finally came on the night of 12 December 2009. It was very clearly predicted and on 10 December I cut down the Musa basjoo stems to ~1m high and completed the winter protection. I then discovered that two other stems were producing flowers. We cut off the flowers and the photographs below (with cm ruler) give an impression of what you can expect. The big questions in my mind are what was special to cause flowering for the first time this year and what can we do to render this a regular event, short of constructing a winter greenhouse around our Musa basjoo. As with many things these days, I turned to the Internet for inspiration. When one does a dedicated search on “fruiting and flowering”, it becomes clear that other gardeners in cooler climes also share the sort of experience I have described. However, there is nothing of substance to be found which describes how to set about getting regular fruiting and flowering under the sort of growing conditions which we have here in the central Netherlands where one really has to assume that winter minimum temperatures will hit at least -10 deg C with the knowledge that they can also go much lower despite all the milder conditions which increasingly occur. An article from New Zealand ( http://www.subtropical.co.nz/writingBanana06.html ) basically summarises the sort of cultivation requirements to favour fruiting in Musa basjoo.
In summary, get leaf production going as soon as possible and ensure that potash (potassium) is available to promote flowering and fruiting. Thinking back, the cold 2009 spring certainly didn’t help with early leaf production although it did commence from good, thick stems about 1m high and which were at least 2 or 3 years old . In previous years growth also came from protected stems but feeding was limited to a good load of well-rotted cow manure on the philosophy that it needed plenty of nitrogen to put back all the green stem and leaf I took off it prior to winter.
In 2009 I was rearranging the tropical border and the banana was basically left to get on with things but I did throw it generous handfuls of a general fertilizer at regular intervals. In other words, for the first time in it’s life, our Musa basjoo received a balanced diet and not one incredibly rich in nitrogen. When one recalls that one symptom of a plant which is fed on a diet of fertilizer in which one of the key NPK components is essentially overdosed is an apparent deficit of the other two main components, then the lack of flowers on an otherwise very vigorous banana clump is possibly explained. I have been part-starving it in my drive for maximising leaf growth!
The winter of 2009/2010 started late but seemed to go on for ever and it seemed that late frosts had randomly killed some of the stems I had cut back prior to protecting the plant in late November. After a little thought on this, the realisation dawned that the die back was nothing to do with frost but with the fact that the “afflicted” stems had born fruit or flowered the previous year. With the advent of warmer weather from about May, numerous new shoots started to push up from around the bases of the dying stems. These developed rather slowly at first but accelerated as the summer began to draw to a close from about early September. Maybe other established stems which had not flowered monopolised the food and drink in the spring and first half of the summer as they formed new stem and leaf matter and once their rate of growth slowed, more food became available for the new shoots (?) Well, that is a hypothesis which accounts for what I observed but I’m open to other ideas. The important thing is that my Musa basjoo has become much more of a thicket of stems than before it flowered and, much as is the case with some bamboos, I will have to decide on whether I want to thin out and perhaps pot up the shoots with some root or not. So, assuming that my plant survives the coldest December (2010) since records started over a century ago, this decision will be taken in 2011. Oh yes, before I close this update, it is important to note that there was no sign of flowering in the 2010 season and there has been none since.
For information, a very interesting article entitled “The origin of Musa Basjoo” by David Constantine in the Plantsman, (vol 7, part 3, p156-161, 2008) points out that the popular association with the “Japanese fibre banana” is quite possibly incorrect. Fibre is/was produced from a less hardy banana grown on the Ryuku islands and nobody less than von Siebold compounded the confusion. M. basjoo is most likely a purely decorative garden plant which Japanese gardeners introduced from China.