By Cuttings: This method of increase is mainly confined to the named varieties of double, pendula and the bedding varieties, or those possessing some characteristic feature of sufficient importance to render them worth preserving. Cuttings can be taken in early spring, when the young shoots from the tubers are two or three inches long, or in the summer making use of the side shoots taken off with a 'heel'. The young shoots taken off in the spring (like dahlia cuttings) and inserted in well drained pots of open sandy soil kept in gentle heat will take root and make plants more easily than those obtained by any other method. It must, however, be borne in mind that unlike dahlias, they will not produce crop after crop of cuttings. It is rarely possible to sever more than one or two cuttings from a single tuber and, indeed it will not be possible to remove any from the majority of tubers, as enough shoots must be retained to produce a plant. As a general rule this method of propagation is possible only from old tubers which occasionally produce more shoots than are necessary to furnish the plant and by far the most commonly adopted method of propagation is by taking the side shoots. These side shoot cuttings are the growths which are produced in the axil of the main stem and leaf stalk. They should be about four inches long and are removed by making cuts with a very sharp, narrow-bladed knife-firstly, parallel with the main stem and secondly, parallel with the leaf stem. This second cut will, therefore, naturally be diagonal to the first and will meet the latter which will enable the cutting to be removed easily. At the base of the cutting or side shoot is a fleshy bract enclosed in which is a veiy small 'eye.' It is essential that this 'eye' should remain attached to the cutting and be undamaged, as it is this, remaining dormant on the cutting tuber until the following season, which produces the shoot which eventually makes the new plant. The cuttings, when removed from the parent tubers or plants, should be potted singly into small thumb-pots in a mixture of equal parts of loam, leaf mould (or peat) and sand. Place the cuttings against the side of the pots, make the soil firm around them and put them in a house which is kept warm, humid and shady, with a little bottom heat if possible. A portable propagator placed on the staging, similar to that suggested for use in seed sowing, will prove useful and is indeed almost essential, though some growers seem to succeed with their propagations by just covering the cuttings with papers on an ordinary greenhouse staging covered with ashes and peat to retain moisture. Callousing will commence in about 14 days and within another 14 days small roots should begin to emerge from the edge of the callous. It must be remembered, however, that some varieties take longer to root than others and it must not be expected that all will be ready to be removed from the propagator at the same time. But when rooting has taken place, light and air should be admitted as this will further encourage root action. It is important not to let the cuttings wilt, particularly when first placed in the propagator, or rooting will be retarded, if not entirely prevented. If the cuttings are rooted early in the season, say June or July, they can be repotted into 4 inch or 5 inch pots and if this is done sizeable tubers will be produced. But as a general rule this repotting is not possible and the cuttings remain in their first pots for the entire season. An occasional feeding with a weak liquid manure will keep them from becoming starved and the resultant small tubers, varying in size from one and a half inches will make nice plants if started in the usual way the following year, though they are inclined to be somewhat later starting into growth than the tubers raised from seed.
Cuttings taken late in the season, say August or September will naturally be very late in going to rest and it is not unusual for them to retain green foliage until late December, or even early January. Even if this should occur they must not be forced to rest by withholding water entirely or by any other method, or the immature tubers will not survive the winter, as it is only by allowing the cuttings to die back naturally that the tubers will be formed. In any case the tubers of the later rooted cuttings will be smaller than the earlier rooted ones and may be no longer or larger than a finger nail. Even so, if correctly ripened, they will produce good plants the following season and rooted cuttings can prove quite useful for late flowering the following year. As a general rule it is advisable to finish propagating by July and cuttings which have been rooted in June are the most satisfactory from every point of view.
The best cuttings are those which have been taken from plants growing slowly in a well ventilated and well lit house. Plants growing in a very warm, humid atmosphere and in a heavily shaded house, produce cuttings which are long and soft in texture and are therefore more liable to 'damp off when placed in the propagator. For the same reason cuttings taken from plants which have been given an excess of nitrogen should be avoided as they too will be soft and probably fail to root. Cuttings having the best texture are usually found at the lower part of the main stem; those which appear above the fourth leaf should not be used.