Few gardeners are satisfied just to grow lilies: they want to do more than that; they want to multiply them. Two methods are possible – either from, or vcgctatively.
Vegetative reproduction means taking a part of the living lily and growing it on, with care, to produce another plant exactly like its parent. The process is carried out in a number of ways, and is the only certain method of obtaining plants identical to the original stock and the only method by which hybrids, to be identical, can be multiplied.
Multiplication by bulb division
Bulbs of Tigrinum, Umbellatum, and Davidii hybrids double every year; during the first year they are divided into two parts by the maingrowing from the centre, and by the second year each of the easily parted sections is capable of producing a flowering lily. Bulbs of Mid-century and Tigrinum hybrids, and some others, are therefore best lifted and divided every year to keep the ever-1ncreasing clumps of bulbs from weakening plant growth and flowering ability. Work of this nature should always be completed before new growth has started, during autumn and spring, which is not only the correct time for separating the easily parted bulbs, but also for transplanting the surplus.
The Bellingham hybrids and also the American L. canadense, L. pardalimim, L. harrisianum, L. superbuin, L. washingtonianum, etc., are either rhizomatous or stoloniferous, and develop new bulbs on their underground stem system. A sharp knife soon separates them, followed by individual replanting, but if they are to be kept vigorous, regular lifting and division are necessary every four years, particularly with the rhizomatous L. pardalinum and L. harrisianum.
Multiplication by underground bulblets
When spring growth first commences, some lilies, including L. dauidii var. willmottiae, L. wardii, L. duchartrei, and L. nepalense, produce undergroundwhich, after wandering along below ground, suddenly break through the soil surface, but not before bulblets have started to build up on the intcrnodes. Bulbs also form on the parts of the stem which remain underground – particularly if the bulb has been planted fairly deeply – and often provide a very prolific means of increase. Stem-bulblets are regularly formed by lilies which split their bulbs annually; this is also the case with trumpet lilies, L. henryi, the Aurelian hybrids, and especially L. longiflorum (37). Autumn is the best time for lifting and replanting stem-bulblets.
Multiplication by axil bulbils
A number of lilies produce bulbils in theiraxils: L. bulbiferum, aptly named on account of this habit; L. tigrinum;L. sargentiae; L. sulphureum; and many hybrids. Axil bulbils are small and should be planted in after removal from the parent plant during summer or autumn; they often produce during that very same autumn, and certainly during the following spring. Removal of, or accidental damage to, flower buds on the upper parts of the flowering stem aids both axil bulbil and underground bulblet production. This is a remarkable phenomenon well worth remembering, as it provides the only means of retaining a valuable lily if its main stem has been accidentally damaged. But axil bulbils and stem-bulblets can also be produced if the stem is cut % into several pieces and each part, including leaves, is planted vertically in a mixture of sand and peat and kept at a temperature of 68-77 DEG F (20-25 deg C). This method is, of course, particularly valuable for the of lilies where stem damage has taken place close to ground level. Some lilies which do not normally produce axil bulbils can be induced to do so provided they show no flower buds at the time: eminently suitable are the hybrids of L. leitccuithwn var. ceiitifoliiiiir. L. sargentiae, L. sulphurewn, and L. tigrinutn. Seedlings or young plants of such hybrids raised from bulblets kept in the warm and very humid atmosphere of a closed , produce numerous bulbils at all the internodes of the stem which remain above ground level. Most of the newly formed bulbils grow short and leaves, and are easily removed from the parent plant for immediate planting. This rapid method of multiplication is often used if a new lily is to be quickly brought onto the market. If the plant produces a flower, the formation of axil bulbils does not take place.
Multiplication by bulb scales
This is the usual and normally the most rewarding method. As soon as flowering stops, the lily bulb is lifted, and some of the scales (often up to 50 per cent of them) are carefully severed from the lowest possible point of attachment to the bulb plate. After allowing the wound to dry, the scales are treated with a suitable proprietary fungicide (scales and a level teaspoonful of fungicide are put in a tin and well shaken) which should be based on cither Captan, Ferbam, Mancb, or Thiram (TMTD). The bulb, prior to replanting, should also be dusted with fungicide. Scales are nearly as easily removed from bulbs left in situ, provided a hole is first dug at their side; the scales are then carefully removed, and on completion of the operation the bulb is dusted with fungicide and the soil replaced.
If scales are to produce satisfactory bulbs, they must be subjected to a humid, warm atmosphere. In Oregon, scales are scattered in shallow drills on open land and lightly covered with soil. Within four to six weeks the small, newly developed bulbs produce leaves, and they 51 continue to grow until late autumn. Other methods must unfortunately be used in regions not favoured with the Oregon climate, where heavy autumn rains terminate the necessary period of warm, humid conditions too early in the growing season.
Scales previously treated with fungicide are put into a sufficiently large polythene bag which contains damp peat, damp vermiculite, or sphagnum moss. The closed polythene bag is then stored at a temperature of 68-72 DEG F (20-22 deg C) in a warm cupboard or in the kitchen; for native American lilies a temperature of 5Q-68 DEG F (15-20 deg C) is sufficient. With some varieties, the small bulbs growing from the callus occasionally take months to develop; others take only four to six weeks, but normally the newly developing bulbs reach pea to hazelnut size within a few months.
Bulbils must be subjected to a period of cold treatment to inducegrowth if they are to be planted in the open or in or boxes during the following spring. This is achieved simply by storing the plastic bag in a cool cellar or in a coldframe, or even in a refrigerator, for two to three months at temperatures ranging from 36 deg to 46 DEG F (2-8 deg C). Unless young bulbs and axil bulbils receive this treatment, leaf development is likely to be very poor or even nonexistent. Before the bulbils are planted they need to be most carefully separated from the now-exhausted scales to avoid damage. If, however, some of the scales are still sound, healthy and sappy, they can again be subjected to the warm treatment to produce still further bulbils.
An alternative method is to grow the fungicide-treated scales in boxes or pots filled with vermiculite or a peat and sand mixture. The long side of the scale – or, the side with the broken edge – should be pressed into the growing medium, and theshould be covered with a sheet of polythene well tied round the sides and placed, as previously, in a warm . Although pots and boxes need more storage space than plastic bags, the method is ideal if a warm greenhouse is available. It also has the additional advantages of reducing disturbance to a minimum, and postponing the operation of planting-out until the first summer.
Scales can be encouraged to produce more numerous, though small, bulbils is they are lightly cut along the broken edge with a sharp knife. Particular care should be taken that the growing medium, of whatever kind, is not too wet; it should be only slightly damp, so as to feel almost dry if touched with the back of the hand – excessive moisture invariably gives poor results. Peat is undoubtedly the best material to use, as it seldom leads to failures, and retains moisture more evenly and for longer periods than most other growing mediums.
Multiplication by scales can take place at any time of year, but the provision of a rest period, after two to three months of warmth, is important. Finally, a warning – the scales of some hybrid lilies can take longer than six months before they start to produce bulbs.