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The Culm Before The Storm

The exotic garden is certainly not complete without a Bamboo or six. Simon Olpin makes some suggestions
Dr Simon Olpin, 124 Dobcroft Road, Eccleshall, Sheffield, UK
Chamaerops No. 17, published online 23-07-2002

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Above: Trachycarpus fortunei (the Chusan palm), Thamnocalamus tasselata, and Sinarundinaria murielae, together with ferns and cordylines in Simon Olpin’s wonderful garden.
Below: Phyllostachys nigra showing cascading foliage, with Trachycarpus and phormiums

Looking out of my living room window on a cold and wet February afternoon, my garden still looks surprisingly green and fresh, despite a winter which has delivered us far more than our usual quota of winter gales, lashings of rain, and on one occasion, six inches of snow.

This greeness is largely maintained by a good mix of evergreen trees and shrubs, including, over ten Trachycarpus of various sizes, phormiums, yuccas, cordylines, arbutus and eucalyptus and even a much branched lOft Echium pininana. Although, in all honesty, the latter can hardly be said to offer much green lushness having just scraped through the winter with some direct protection.

However, for me the real heroes of the winter lushness are the bamboos, which, if chosen carefully can provide architectural structure and shelter even to the coolest of British gardens. Indeed, the strategic siting of bamboos around palms and other exotics not only complements and enhances the tropical effect, but actively promotes it by protecting many of these other plants against the ravages of the winter storms. It is true that bamboos do not like direct exposure to strong winds, but within the primary shelter of garden boundaries they can be used to dampen down winds and create a protected microclimate within the garden. Some species are more wind tolerant than others, and while many bamboos will withstand fairly strong moist west and north-westerly winds, it is the cold and drying easterlies that can do most damage. When this does occur however, the new season will see new leaf and culm growth, which will quickly replace the damage.

I live on the edge of the city of Sheffield which is situated in a giant bowl on the south-eastern edge of the Peanines. Several large valleys run down the sides of the bowl producing marked folds in its surface. The actual city centre is only about 300ft above sea level, but quite large areas of suburbia are between 600ft-1000ft. This means that there are considerable climatic variations within the city boundaries, ranging from high exposed moorland to sheltered wooded valley bottoms. My garden is situated at 450ft above sea level on a south easterly facing slope and has only moderate exposure to the north and northwest being about 150ft from the valley bottom.

My primary windbreaks are a long but rather sparse beech hedge, some conifers and hollies, and a number of large sprawling rhododendrons. Within these confines I have set out to create my own 'subtropical' garden.

I use hardy evergreens such as yuccas, fatsia, eucalyptus, arbutus, yew and holly, while relying quite heavily on bamboo to create the basic subtropical structure. Amongst these, I grow fairly hardy exotics, such as phormiums, palms and cordylines, some of which need protection in the severest weather. I overwinter tender exotics, such as agaves, hedychiums, cannas, callistemons, puyas, coloured cordyline and some palms in a conservatory and greenhouse and bring these into the garden for the summer months.

While bamboos survive the severest of winter weather unprotected it is advisable to provide a thick mulch of well-rotted compost or manure, annually, preferably in the autumn, as this reduces frost penetration to the roots, promotes healthy growth by way of extra nutrients and helps to retain moisture.

Snowfall can be frequent and heavy during an average Sheffield winter and this can do considerable damage to some evergreens, although its insulating qualities are a bonus point. In fact it is rare for us to have a sustained cold spell without the advantage of an insulating layer of snow. Despite the frequency of snow, I have experienced no significant snow damage to bamboos. Moderate to large species such as Phyllostachys, Sasa, Pseudosasa, Thamnocalamus and Fargesia are frequently flattened by snowfall. Under these circumstances it is best to leave well alone, as under these conditions the bamboos are well insulated against subsequent frosts. When the snow melts the culms spring back up again as though nothing untoward had happened.

The Bamboos

The Phyllostachys bamboos are a large group of tall bamboos of 12-25ft in height with calms of up to 2 inches in diameter. In general they grow more vigorously and attain their largest proportions where summers are long and hot, provided there is adequate moisture. However, this should not deter those from cooler p arts of the British Isles from growing these lovely bamboos. Under cooler conditions they merely attain more modest proportions and in some species they tend to take on a less erect and more arching habit. The Phyllostachys are for the most part only moderately invasive, while displaying a fine range of highly decorative culm colouration, particularly in some of the more recently introduced cultivars. Colours of mature canes range from the bright yellow of Phyllostachys bambusoides 'Holochrysa' through the yellow with a bright green stripe m the groove of Phyllostachys bambusoides 'Castillonis' and the orange-purple staining with deep green in the groove of Phyllostachys aureosulcata 'Spectabilis' to the jet polished black of Phyllostachys nigra. Phyllostachys aureosulcata 'Spectabilis' along with Phyllostachys bissettii are particularly hardy bamboos and to be recommended for the more northerly garden. Phyllostachys aurea and its fine cultivar 'Holochrysa' with golden-yellow mature culms and lime-green foliage often with a thin yellow stripe in early season leaves, make smaller but very statuesque bamboos having only attained about 8ft in height with me to date. The crowded node bases of P. aurea are a notable feature. P. nigra is another highly desirable bamboo, which should be grown in full sun in a sheltered position to show of its best. Under such conditions it has rewarded me with fine black polished culms ad masses of cascading dark green foliage.

The stately habit of many Phyllostachys bamboos makes them particularly suitable for growing close to water. However, it must be borne in mind that bamboos in general will not tolerate water logging, but, being shallow rooted, they can be grown on a raised area of as little as one foot above the 'high water mark'.

A number of other genera of bamboos, particularly those from high mountain regions are well suited to the cool moist maritime climate of Britain. Amongst these are the Chusqueas, a large group of over 100 species, from South America, with solid stems and varying habit. However, at present, only a few are grown in Britain, although it is likely that more will become available in the future. The best known is Chusquea couleou. This is an extremely desirable bamboo, although being somewhat variable in form. Good specimens are breathtaking plants, attaining formidable proportions of up to 2Oft in height and even more in circumference. Culms are well spaced in mature specimens and up to one inch or more in diameter. Branches are borne in dense tufts at each node, giving a striking bottlebrush effect. It is a very hardy bamboo, but dislikes long hot summers, although this is generally not a problem in Britain. A superb specimen at the Royal Botanic Gardens in Edinburgh is a testament to its preference for cool growing conditions. Unfortunately, it is difficult to obtain, following some years when fresh viable seed has been available, this source seemingly has dried up, and vegetative propagation is sadly a slow and difficult process. A young Chusquea couleou in my garden was planted as a small seedling from a six inch pot in August 1990 and is now 7-8ft m height and equal in circumference, having produced over 40 new culms last year alone.

Other tall bamboos which thrive in our climate are the clump forming and familiar Sinarundinaria murieliae and S. nitida (now Fargesia murieliae). These are elegant and very hardy bamboos reaching 10-12ft in most growing conditions, and forming ultimately a large and very dense clump. However, a word of warning here in that F. murieliae has shown sporadic flowering over the last four years or so, and most expert opinion suggests that in due course all specimens in the U.K. will flower and eventually die, having originated from the same clone. Those of us with fine specimens of this lovely bamboo would be well advised to cultivate a replacement, in anticipation of the worst. Small seedling plants of this most recent flowering are becoming available and are most unlikely ever to flower again in our lifetime.

Thamnocalamus tesselata, the South African bamboo, and Thamnocalamus crassinodus and Fargesia robusta make fine hardy bamboos. Indeed, a specimen of T. tesselata provides a fine windbreak and backdrop to a large Trachycarpus fortunei in my own garden. This bamboo remains undamaged even when exposed to quite strong northerly winds.

A shorter, but for me, an indispensable bamboo is Sasa palmata nebulosa. This vigorous, extremely invasive, but easily controlled bamboo, forms dense spreading clumps of curving culms 6-9ft high topped with large paper-thin leaves of 12" in length and 4" or more wide. The impression is of a very tropical and lush plant that is in fact extremely hardy and very happy under cool moist growing conditions. It looks particularly good when its lush foliage is contrasted against the much smaller leaves of C. couleou or T. crassinodus.

Not all bamboos have plain green leaves, and in recent years an increasing number of variegated and coloured leaf forms have become available. Notable, among these is Pleioblastus viridistriatus chrysophyllus, (now P. auricomus chrysophyllus) a golden yellow form of the yellow and green striped P. viridistriatus. Both forms are very pleasing and decorative small bamboos of up to 3ft, with a slowly spreading habit. A taller (up to Oft) and rather striking bamboo is Hibanobambusa tranquillans 'Shiroshima' with large leaves having spectacular creamy white bands, often tinged pink when young. However for me the best new introduction is Sasa kurilensis 'Shimofuri' looking like a small S. palmata in form, its leaves having numerous thin white stripes.

There is no doubt that the bamboos can provide that extra year round exoticism to any garden, while complementing other exotics, particularly palms, and other large leafed evergreens with their contrasting foliage and form with the added bonus of the protection of the 'CULM BEFORE THE STORM'

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