This section is from the book "The Gardener V2", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
It would be easy to make an extended list of beautiful and useful species of Acacia for general decorative purposes without exhausting the list of those which are or have been in cultivation. It is a large family, and varied and interesting enough, botanically considered; but for the simple purposes of the garden or the decoration of the greenhouse, a very small selection will suffice. The fact that there is little variation of colour in the family settles this point. So large a group of plants, with the same colour repeated in nearly every member of it in slightly varying shades, as it is in this, can hardly be singled out from the whole range of the vegetable kingdom. Therefore, except in the case of large collections, of which there are few or none worthy the name in private gardens, a limited number of the greenhouse species will suffice for the purposes of introducing greater variety into the furnishing of the greenhouse in winter and spring, which is all that in these papers will be advocated. And here let me explain, that I aim only at rousing some general interest in the value of hard-wooded or shrubby greenhouse flowering-plants, wherever the circumstances of the garden admit of their being introduced more largely than they are at present.
I do not think that they are adapted to the circumstances and necessities of all places. Small places, where the stock of plants of all classes commonly cultivated and requiring greenhouse protection is lodged in one or two houses, cannot devote any part of their glass space to the special culture of these plants without sacrificing much of the enjoyment which it affords as at present, stocked in the main or wholly with soft-wooded plants. The treatment required by shrubby and herbaceous plants is so opposite, that they cannot well be grown together in the same house the year round. They may be flowered together, but that is all they will submit to in the shape of general treatment. The culture in each case must be somewhat different up to this point, in order to grow them well and have a full development of flower but for the time they are in bloom, they may stand together in the same house without detriment to each other, provided there are pits or houses to which they may be removed afterwards, and be separated and put under the treatment they severally require. Acacias are better adapted to being grown in collections composed of hard and soft wooded plants than many other hard-wooded subjects.
They are generally plants that are easy to cultivate, and require the common treatment of greenhouse shrubs, without any of the niceties that have to be observed in the case of some others. Good fibrous loam, with a liberal allowance of sharp sand, suits them admirably. Fibrous peat, if very good, may be used to lighten heavy close loams where the lighter fibrous sorts cannot easily be got; but indifferent peat is a bad component in any compost, and should be used sparingly for all pot-plants, except those which are known to require it specialty. Drainage is a point which should be attended to carefully. Young plants are usually raised from seed or cuttings of the roots. The latter make very good plants, but on the whole and in most cases the best are got from seed, and with the least trouble. Plants that are a few years old usually ripen plenty of seed, so that there is no difficulty in keeping up fresh vigorous stock to any reasonable extent if care is taken to save a sufficient quantity of seed when it is anticipated it may be required. Cuttings of the shoots rarely succeed, except where the means and the skill in propagating exceed the average about private places.
The plants are easily enough grown to considerable dimensions in a year or two - some sorts, of course, growing more rapidly than others; but this end should never be sought after by means of large shifts. It is better to give two small shifts in the year than one large one, - a point to be borne in mind by all novices in the culture of greenhouse shrubs; for though things may appear to go on swimmingly for a time, a foundation of difficulty is often laid in the circumstance that the ball of earth is only half filled with roots, and therefore liable to sour and injure such roots as may find their way into it. Some care should be exercised after potting for some time, in order to prevent the earth from becoming too wet or too dry. After flowering is over, the plants should be cut more or less back, according to the habit of the individual sorts, with the view of preventing leggy or bare specimens, and balancing the growth; and seed-pods should be picked off early after they are set, unless they are wanted for the purpose of increase. The plants may remain in the greenhouse for a time, to make growth after being pruned; and when growth is well started, that is the best time to pot established plants requiring only a little annual attention in this respect.
In the milder and drier districts they may be placed out of doors in summer with advantage, to ripen their wood; but in cold wet ones they are better accommodated under glass, so as to be protected from drenching rains. The glass need only, however, be used when necessary, as in bright dry weather they will be benefited by a very free exposure to sun and air.
Among the most useful species for general cultivation, A. armata is one of the best of those having comparatively compact growth, and it is one of the best known, being frequently to be seen in even limited collections.
Acacia Platyptera is one of the least generally grown, and yet among the most deserving, were it only on account of its flowering in late autumn or winter, one of the dullest periods of the year. It is naturally loose and straggling in growth; is not, in fact, capable of being formed into a bush without being tied to some supports, but well adapted for covering pillars or the back wall of a greenhouse, in either of which cases it makes a very beautiful object, and furnishes large supplies of cut flowery The peculiarly-winged stems of this species, profusely adorned with the orange-coloured globose flower-heads, are beautiful and interesting; and the stems being very elastic, are well fitted for many purposes of table decoration when cut.
I slightly alluded to the surpassing excellence of this fine species in my last paper, and would here again remark on its peculiar beauty and fitness for clothing pillars or rafters in the greenhouse. Those who may have seen it well done in this way will not rest satisfied till they have tried their hand on it in their own case, if the facilities are within reach; and nothing certainly is more easy to cultivate than this fine plant when it is planted out in a border, where it may ramble free at the roots and have corresponding liberty above. Like all other Acacias, it is the better for a little annual trimming with the knife; but as wherever it is grown it is sure to be cut more or less for table and room decoration, all that will in most cases be necessary in spring is a little regulating of the principal branches, so as to keep up a proper balance and free production of the long annual shoots which are found so useful when cut for dressing rooms and vases.
Acacia Drummondii makes a very handsome specimen when well grown. There are several varieties, some of which are not worth growing. They vary, as most plants do, somewhat from seed; and it is the more desirable in such a case to raise the stock from cuttings either of the root or branch; and the latter, it should be known, are not so difficult to manage as in some other species. Unlike the previously-mentioned species, the flowers of this are oblong; and it is chiefly in their relative length that the varieties differ, though there is also more straggling and loose growth, accompanied with the inferiority of the flowers alluded to, which renders it impossible to form the plants into handsome dense-blooming specimens.
A very handsome species, of very dwarf and compact growth, flowering profusely, with the flowers globose and orange-yellow. This, with Acacia armata and Acacia hispidissima, are among the best for small collections or small houses, neither of them being very rampant in growth, nor difficult to keep in health in circumscribed limits.
Acacia Sjpectabilis is of rather large growth, with handsome glaucous pinnate foliage; and when it acquires a little age, it is one of the most profuse flowering of the family.
Acacia celastrifolia, like the last, is a strong grower, but with the leaves or phyllodia simple - not pinnate, as in it - and the flowers large.
Acacia dealbata, grandis, and lophantha, are species remarkable for the graceful character of their leaves, which are beautifully pinnate, and in the two former glaucous, but in the latter green. They are only adapted for large houses, as they quickly outgrow the space in small ones. W. S.