Hardy bamboos have long been known in gardens under three generic names, viz., Arundinaria, Bambusa and Phyllostachys. Whilst most of the species of Phyllostachys are probably correctly placed, so much cannot be said for those put under Bambusa and Arundinaria, many of which had never been critically examined in flower at the time they were named. True species of Bambusa, perhaps with one exception, are not hardy in the British Isles; the exception – B. glaucescens Willd. (B. nana Roxb.) of which there are several attractive cultivars – might be grown in the open in sheltered positions in the south-west.
As regards Arundinaria, American, Chinese and Japanese botanists have made extensive studies, in the field, of hardy bamboos during the past forty years, with the result that many species classified in the genus Arundinaria (sensu lato) have been referred to the following new genera:
chimonobambusa Makino – A. marmorea
pleioblastus Nakai – A. simonii, A. graminea, A. humilis, etc.
pseudosasa Makino – A. japonica
sasa Makino & Shibata – A. palmata, A. ragamowskii, A. veitchii, etc.
semiarundinaria Makino – A. fastuosa
sinarundinaria Nakai – A. murielae, A. nitida
tetragonocalamus Nakai – A. quadrangularis
Also, the genus thamnocalamus Munro has been revived and to it are referred A. falconeri and A. spathiflora. With regard to the use of these generic names in this work, it has been decided to retain most species in Arundinaria as hitherto except for the three species A. palmata, A. ragamowskii and A. veitchii, which are referred to Sasa (q.v.). To assist those interested in the proposed division of the genus, the various new generic names are given prominently under the species concerned. The nomenclature of these hardy bamboos is still in an unsettled state, as some should probably be treated as cultivars, others are based on imperfect descriptions, while quite a number of species have not flowered, so that their precise generic position is uncertain. If the new classification were to be adopted only two species of Arundinaria hardy in Britain would be left in the genus, viz. A. gigantea (A. macrosperma) and A. tecta, both natives of the United States.
The following remarks concerning cultivation, etc., although placed under Arundinaria, are intended to apply to the hardy bamboos in general; other genera described in this work are Chusquea, Phyllostachys, Sasa and Shibataea.
The bamboos are really woody grasses, mostly characteristic of moist tropical and warm temperate regions, the species in cultivation being mainly from the Himalaya, temperate E. Asia (China, Japan, Korea and Formosa), the United States and the Andes of S. America (Chusquea). Although they are mere pygmies compared with the giants of equatorial regions, they have a special value in our gardens in introducing to them a form of vegetation not only of surpassing grace and beauty, but one of an absolutely distinct type.
Naturally they are evergreen, but in cold winters and in cold districts some of them lose much of, or all, their foliage. They have hollow stems divided into sections by a transverse woody layer at each node (or 'joint'), and the branches (from one to many) are produced at these joints, which are farthest apart about the middle of the stem. In the young state the stems are more or less encased in membranous, papery or coriaceous sheaths which in some species fall away, in others persist. At the ends of these stem-sheaths there is usually a leaf-like expansion known as the limb or blade and at the base of the latter often two lateral outgrowths known as auricles, which usually bear hairs or bristles. The stem-sheaths provide valuable distinguishing characters, differing in texture, whether hairless or hairy, in colour and whether spotted or blotched with a deeper coloration, also in shape and size, the presence or absence of auricles, the form of the auricular hairs and the shape and direction of the blade. They are most useful, when associated with other parts of the plant, for purposes of identification.
The leaf-blades of bamboos have a midrib supported on each side by from two to twenty more or less prominent secondary veins, between which again are thin, delicate veins of a third dimension, easily visible by holding the leaf between the eye and the light. In all but two of the species mentioned in these notes the thin veins are united by tiny cross-veins – easily seen with a lens by holding the leaf up to the light – which divide the space between each longitudinal vein into rectangular spaces of irregular size. Lord Redesdale made the interesting discovery that this tessellation of the veins is invariably characteristic of a really hardy bamboo; those that do not possess it are as invariably tender. This, however, does not mean that every bamboo with a tessellated venation is hardy. The leaf-blades are frequently narrowed to a short stalk at the base where they join the leaf-sheath, which is easily detached by pulling at the blade. At the junction of the sheath and blade many species bear a pair of lateral outgrowths – the auricles – which are usually fringed with few to several rough or smooth bristles. These auricles, like those of the stem-sheaths (see above), are useful distinguishing features.
In habit, bamboos are either tufted – i.e. they keep their stems in a close cluster and extend but slowly – or they spread by means of underground rhizomes, which may be short or long, giving rise to erect stems at intervals, which in some species push through the ground several feet away from the older stems (e.g. Arundinaria anceps).
The flowering of bamboos is a phenomenon of peculiar interest, but as the flowers have little bearing on the identification of those we cultivate, it is not necessary to enter into a definition of them here. On many of the sorts we grow they have never been seen in this country, nor, indeed, ever examined by botanists. For this reason they should be gathered and sent to a botanical institution for examination and, if necessary, preservation. It is only by recording instances of flowering that we shall be able to ascertain whether it occurs at more or less frequent intervals, and whether it is followed by the death of the individual plant. There is no doubt that the flowering of many bamboos is shortly and inevitably followed by their death: Arundinaria falconeri is an example. Others flower and although seriously crippled, in time recover: some of the Phyllostachys behave in this way. In a third group a small proportion of the stems flower, and although those particular stems die, the plant as a whole is unaffected; Arundinaria viridistriata (A. auricoma) is an example, plants of which can usually be found bearing a few spikelets at the tips of the stems. This is not a general (gregarious) flowering, however, but rather of a sporadic nature, isolated stems only bearing a few flowers. It should not be compared with flowering spread over several to many years and the final flowering and death of every stem and its branches such as occurred with A. simonii after blooming partially for at least twelve years; or with many plants of A. fastuosa, which flowered from 1957 to 1968 (or perhaps later) and finally died. It has been reported that the lives of bamboos (or of some of them) may be saved by cutting off all the stems close to the ground as soon as ever there is any indication that they are about to blossom. This is worth trying, although where the flowering is general it has usually been unsuccessful.
A curious circumstance in connection with the flowering of bamboos is the simultaneous flowering of all the plants of one species, although spread over great areas and growing under different conditions. Instances have been known where plants grown in English hothouses for many years have flowered (and died) during the same season as plants of identical species growing wild in the tropics. Hardy species in our gardens have behaved in the same way, flowering simultaneously all over the country as well as in other parts of the world, probably being derived from the same original introduction from the wild state; but the period of flowering appears to be longer and less clearly defined than in the case of wild species, and may extend over four or five years. Good examples of such flowering are Phyllostachys nigra and P. aurea, which flowered in various parts of Europe, S. America, Australia and New Zealand, and E. Asia during the same period of years.
Cultivation. – The most important item in the cultivation of the group as a whole is the provision of good shelter. Few plants we grow are less adapted to withstand cutting blasts from north and east than these. They need some position protected from those quarters, but open to the south and west. Nothing in our gardens is more lovely in form than a well-grown bamboo from midsummer to Christmas, but with the January and February frosts and the biting winds of March, many of them become seared and brown, and anything but pleasant objects. Adequate shelter from cold winds does much to prevent or defer this disfigurement.
As regards soil, they appear to thrive best in an open loam of fair quality; neither so sandy as to be poor, nor so clayey as to be heavy and cold. They also succeed well on a peaty formation. Being gross feeders they need abundant moisture, and are benefited by occasional mulchings with manure, leaf-soil or humus of any kind, particularly during dry springs and summers.
Transplanting and Propagation. – In the absence of seed – a very uncertain product in this country – propagation is effected by division. All disturbance at the root, whether for propagation or transplanting, is best deferred until May, or until the unfolding of new leaves indicates that root action has begun. Early autumn is also a good time, but from late autumn to early spring is the worst time to transplant. In order to divide some clumps of the tufted sorts it may be necessary to use a pickaxe, so hard and matted does the root system become; but from the running sorts pieces can be easily detached. To get a big stock quickly, a clump should be broken up into comparatively small pieces, which should be potted or planted thickly in a warm, moist greenhouse until re-established. In this case it is advisable to cut down the stems in proportion to the sacrifice of roots. Imported plants are safer if established in heat in this way before planting in the open ground.
For districts where the success of bamboos is problematical the following sorts are the best to experiment with: Arundinaria anceps, A. fastuosa, A. japonica, A. nitida; Sasa palmata (Arundinaria palmata), S. tessellata (.Arundinaria ragamowskii); Phyllostachys nigra and P. nigra 'Henonis'.
Arundinaria. – The most obvious distinctive characters of what we have been growing as Arundinaria are in the stems. These are round and straight, and develop the branches almost simultaneously from top to bottom, and, in the taller species, the branches at each joint are indefinite and numerous. The low, slender-stemmed, sparsely branched, very rhizomatous species included in previous editions under this genus, namely A. veitchii, A. palmata and A. ragamowskii, will be found in Vol. 3 under Sasa, the genus into which they have been separated by Japanese botanists.
The following species of Arundinaria are not treated in the present work: A. hookeriana Munro (E. Himalaya), A. intermedia Munro (E. Himalaya) and A. khasiana Munro (Assam). They are not hardy at Kew but are grown in the open in the mildest parts of south-west England and of Ireland.
Revised by Dr C. E. Hubbard.
From the Supplement (Vol. V)
For recent reports on the flowering of bamboos in British gardens, see the articles by David McClintock in The Plantsman, Vol. 1, pp. 31-50 (1979) and The Garden (Journ. R.H.S.), Vol. 109, pp. 233-5 (1984). The author remarks that no established plant is likely to die as the result of flowering unless growing in unfavourable conditions, but it may take several years to recover. The two commonest tall-growing bamboos in British gardens – A. japonica and A. jaunsarensis (anceps) – have both been flowering profusely since the early 1980s, and the consequent die-back of the leaf-bearing stems has caused problems in gardens where they are used for screening or shelter.
For an up-to-date taxonomic treatment of the cultivated bamboos see: The European Garden flora, Vol. II, Part II, pp. 56-65 (1984), contributed by David McClintock.