Propagation of bulbs

Methods of increasing bulbs are of primary importance to the grower who raises them for sale and to the connoisseur who wishes to multiply rare specimens. They are of interest also to home gardeners who wish to obtain stocks inexpensively or who would like to try some of the fascinating ways by which bulbs may be propagated. This discussion does not concern commercial practices.

Bulbs are raised from seeds and from parts of other bulbs which are segregated from the parents and are grown as new individuals. This latter practice is termed "vegetative propagation." Only by vegetative propagation is it possible to multiply hybrids and highly developed horticultural varieties true to their types; seedlings raised ordinarily from such plants differ markedly from, and are often inferior to, their parents.

Seeds may be used to propagate natural species and most natural varieties ( that is to say, kinds that are not highly developed horticulturally but which are cultivated in the same forms as they are found in the wild), to produce new hybrid and new cross-bred varieties and, in some cases, to raise worth-while mixtures in which varieties of colour, form, size, or other factors are clearly evident and are not objectionable.

A gorgeous hybrid amaryllis or a variety of daffodil such as "King Alfred" or "Aerolite" will not reproduce true from seeds, but seeds of the regal lily or of the common grape-hyacinth ( which are natural species) produce plants that duplicate their parents. If one intended to attempt to raise a hybrid between the regal lily and some other kind of lily the only way to go about it would be to pollinate the flower of one with pollen from the other, to obtain fertile seeds, and to raise from these the hybrid progeny.

A gay swarm of tuberous begonias or of dwarf dahlias, none exactly like their parents nor any two precisely alike ( at least genetically ), are readily raised from seeds and are for many garden purposes as useful as selected varieties grown from vegetative propagations.

Seeds

Seeds of hardy bulbs are usually best handled by sowing them in a cold frame either as soon as they are ripe or in early fall in a gritty well-drained soil that contains an abundance of leafmold or peatmoss. If the quantity is large the floor of the frame may be prepared as the seed bed; otherwise sow in flats, pots, or pans and keep these in the frame. Pots and pans should be buried to their rims in sand or cinders so that their contents do not dry too rapidly.

Cover the seeds to two or three times their own diameter with soil. Shade the frame until germination takes place, which in most cases will occur the following spring but in some instances not until a year later, and keep the soil evenly moist but not saturated. Winter freezing benefits the seeds of hardy bulbs but excessive alternate freezing and thawing may disturb them more than is desirable; to circumvent this protect the seed bed with a light cover of salt hay, excelsior, or evergreen branches after the soil has frozen. Seeds of hardy bulbs may also be sown indoors in late winter, in well-drained flats or pots that contain a sandy, peaty soil. Keep the containers in a greenhouse where the night temperature is about fifty degrees.

Seeds of bulbs that are not hardy should be sown indoors in well-drained pots, pans, or flats. The best time to sow is a little before mature bulbs of the same kinds normally start into growth. Thus the seeds of freesias, sparaxises, and other bulbs that naturally begin growing in fall are sown in September, those of amaryllises (Hippeastrum) and tuberous begonias in January or February.

Seedlings of a few kinds grow rapidly—dahlias, for instance, are transplanted within a month of appearing above ground and are handled exactly as are petunias and tomatoes—but most bulbs do not make such rapid development in their young stages. In the vast majority of cases it is advisable to allow the young plants to complete their first season's growth without disturbance in the seed bed and to move them to new soil only at the very beginning of their second season of growth.

A few bulbs benefit from being left for two seasons in the seed bed. Because of the long time that the seedlings are likely to remain undisturbed it is essential to sow thinly, to space the seeds so that the young plants will not be unduly crowded before they are ready for transplanting.

Nearly all bulb seedlings die down when the natural season of rest for their kind comes, but some ( amaryllises, for example) may be prevented from going dormant if they are kept moist and warm . . . and this is advantageous because it considerably reduces the time that elapses before the first flower appears. After the first blooming normal resting periods are honored. Some bulbs bloom in as little as a year or eighteen months from the time the seeds are sown; others take several years.

Separation of offsets

Many bulbs increase naturally by the production of bulblets ( small bulbs) and of new bulbs which develop alongside, near by, or in place of older ones. By separating these and planting them in favourable locations new stocks are easily acquired. Bulblets should not be removed until they have completed at least one full growing season attached to their parents. When they are separated it is advisable to plant them under especially favourable conditions where they will be encouraged to increase in size and attain maturity as quickly as possible. Depending upon their kind, this may mean accommodating them in a nursery bed, in a cold frame, or ( in a greenhouse) community pots or flats; planting them individually in small pots is not generally advisable.

Bulblets should always be planted more shallowly and closer together than mature bulbs of the same kinds and always in sandy, light soil. A good general rule is to cover them to two to three times their own depth with soil . . . although some, such as amaryllises, are planted with their tops protruding. When they have grown to more mature size the young bulbs are replanted at a greater depth and with more adequate spacing.

Gladioluses, crocuses, and other kinds that have bulbs technically known as "corms" produce in addition to new bulbs numerous "cormels" or tiny bulbs about the base of the mother bulb. These have very hard shells and new growth will develop from them evenly and quickly if they are soaked in water for several hours immediately prior to planting. They are planted or sown in spring in much the same manner as are seeds, after having been stored over winter in a cool, frost-free place mixed with barely moist peatmoss.

Basal cuttage

In Holland, where practically all large-flowered hyacinth bulbs are produced, these plants are propagated by injuring the bases of the bulbs in ways that cause each to develop a large number of bulblets. It is a method that can be applied to some other kinds of bulbs and is worth trying if rapid increase is desired and other techniques are not productive.

As applied to hyacinths, the bulbs are dug as soon as they are ripe in July and immediately three deep cross cuts ( dividing the base into six wedge-shaped segments ) are made with a sharp knife in the bottom of each or, alternatively, the entire base is scooped out leaving the interior of the bulb a hollow pointed dome.

The injured bulbs are then spread out bottoms up, are covered with loose soil, and are allowed to remain for about three weeks while the cut surfaces heal and the cuts expand. They are next spread on benches or tables in storehouses where they remain until October, at which time they are planted in outdoor beds. The following June, when they are dug up, little or nothing remains of the mother bulb but as many as twenty or thirty sturdy small hyacinth bulbs are harvested.

Trilliums may be induced to increase by cutting a deep V-notch lengthwise along the upper side of the bulb and replanting it. This affords an effective means of propagating the double-flowered varieties.

Bulbils, tubercles, and stem bulblets

Some bulbs bear small bulbous growths on their stems above ground. These are known as bulbils or tubercles ( depending upon whether they are technically tiny bulbs or small tubers ). These form a ready means of propagation if they are planted at about the time they are naturally ready to fall from the stems. They should be covered to about twice their diameter with light soil. Among plants that bear aerial bulbils or tubercles are tiger lilies, Begonia Evansiana, and cinnamon vine.

A few plants that do not ordinarily produce bulbils can be induced to do so. If the stalks of certain stem-rooting lilies are severed just above the bulb and are potted and placed in a moist greenhouse they will develop them.

Tiny bulbs that form on the stems but below ground level, such as are produced by some lilies, are classed as bulblets although they have the same morphological origin as bulbils and may be used for propagation in the same way. The production of these stem bulblets by some lilies may be encouraged by jerking the stem from the bulb with a quick, positive twisting motion shortly after the flowers have faded and planting it at an angle of forty-five degrees with its lower twelve or fifteen inches buried in dryish soil in a location that is shaded from strong sun.

By fall a crop of strong bulblets will have formed on the buried parts of the stems and these may then be removed and be planted in a nursery bed.

Division

Division, which consists of cutting a single bulb or a clump of bulbs into two or more pieces each containing at least one bud or eye that is expected to produce top growth, is a popular method of securing increase of some kinds of bulbs. Dahlias, achimenes, cannas, and gloriosas are commonly treated in this way and tuberous begonias, gloxinias, caladiums, and some others may be.

Division is done at the beginning of the growing season and it is usually best to subject the bulbs that are to be divided to sufficient warmth and moisture to induce the eyes to plump up and begin growing before actual cutting is done. This makes it much easier to carry out the operation without destroying eyes.

Each division must consist of at least one strong eye attached to a good bulb or sizeable portion of a bulb. The cut surfaces should be dusted with powdered sulphur to discourage decay and the divisions should be planted immediately in loose, sandy, humusy soil that is kept moist but not wet, and be placed where the temperature is encouraging to growth and the atmosphere is agreeably moist.

Bulb cuttings

Bulb cuttings really represent a special type of division that can be used for many true bulbs ( dahlias, cannas, begonias, etc., are actually tubers or tuberous roots ) and is best known because of its employment in the propagation of amaryllises. The author has successfully increased the following bulbs by means of bulb cuttings and there are undoubtedly many more that are susceptible to this means of multiplication: Albuca, Chasmanthe, Cooperia, Haemanthus, Hippeastrum ( amaryllis ), Hymenocallis, Lycoris, Narcissus, Nerine, Pancratium, Phaedranassa, Scala, Sprekelia, and Urceolina.

The bulb-cutting method consists of taking a mature bulb and quartering it lengthways with a sharp knife, then cutting each quarter lengthways into two or more wedges each including a portion of the basal plate of the bulb; these wedges are further divided by sliding a knife down between each third or fourth pair of concentric scale-rings of which the bulb is formed and cutting through the basal plate at the bottom. The resulting fractions are bulb cuttings. Each consists of segments of three or four scales attached to a small piece of basal plate.

The bulb cuttings are planted vertically in a mixture of peatmoss and sand with just their tips showing above the surface and are kept just moist and in a temperature that is somewhat warmer than that which mature bulbs of the same kinds require. In a matter of weeks, or at most a few months, small plump new bulbs will have grown from the basal plate portion and will be nosing out from between the segments of bulb scales and sending strong new roots from their bases. They may then be transferred to flats of light soil to continue their further development. The author's experiments with bulb cuttings have all been carried out in late summer, the cuttings having been made generally in August. Here is a good field for further experimentation regarding kinds that may be so propagated, times of the year that are most favourable, and the best methods of handling.

Cuttings

Some bulbs may be propagated from cuttings consisting of pieces of stem with leaves attached, in the same manner as are geraniums and many other popular plants. Of these, dahlias and tuberous-rooted begonias are the kinds most commonly grown. The cuttings of these are usually made from young shoots that develop directly from the bulb. They should be taken off just as soon as they are long enough, which means when they are two to three inches long. It is better to use the entire shoot than to snip the top off a shoot that has grown too long and employ it as a cutting.

On the other hand it is quite satisfactory to use the upper parts of the stems of achimenes as cuttings. In some cases—dahlias, for example—it is an advantage to take a sliver of the old bulb to form the base of the cutting. In all cases the base of the cutting should be prepared by cutting it cleanly across with a keen knife and this cut should be made, except where a sliver of the old bulb is retained, a short distance below a node ( stem joint ).

The lowermost leaves ( which on cuttings of young shoots arising from the bulb will be rudimentary) are removed and the cutting is planted in firmly packed sand or sand and peatmoss or in not firmly packed vermiculite, is well watered and is placed in a propagating case in a greenhouse, in a terrarium or other place where a humid atmosphere can be maintained.

Here the cuttings remain until roots an inch or so long have developed; then they are potted individually, returned to a close atmosphere for a few days, and then gradually hardened to the conditions that established plants of their particular kinds favour. If the cuttings are provided with bottom heat ( gentle warmth that keeps the rooting medium at a temperature five to ten degrees higher than it would otherwise be ) rooting will be accomplished faster.

During their period of rooting the cuttings are shaded from strong sun but are afforded good light. It is important that cuttings be made sufficiently early in the growing season for them to form bulbs large enough to persist through the dormant season before this begins. It is perhaps worth noting that the author has successfully employed the leafy crown that tops the flower spike of Eucomis as a cutting. He does not recall having heard of this being done before.

Leaf cuttings

Certain bulbs are easily multiplied by using single leaves or portions of leaves as cuttings and by planting them under conditions recommended for regular stem cuttings. Gloxinias, achimenes, smithianas, isolomas, and others in the gesneria family belong here. In the lily family hyacinths, lachenalias, and probably some others freely reproduce from portions of leaves that are cut across horizontally and are planted with their lowermost inch in sand that is kept just moist but not wet. Undoubtedly there are others that will respond in similar fashion. Clivias are reported to respond to this method.

With the gesneriads it is advisable to use whole leaves as cuttings and to plant them at an angle of forty-five degrees with their bases half an inch deep in sand, a mixture of sand and peatmoss, or vermiculite. If stock is scarce it is often possible to obtain more than one offspring from each leaf by cutting the main veins across on the undersides of the leaf at two or three places and then placing the leaf horizontally underside down on a bed of peatmoss or peatmoss and sand. Each cut will generate a new young bulb. The small bulbs formed from leaf cuttings of these plants do not develop leaves until after their first dormant period; the bulbs only are produced the season the cuttings are inserted.

Cuttings of lachenalias and hyacinths should each consist of the upper few inches of a leaf. The bottom of each cutting should be cut squarely across. The cuttings are then inserted half an inch deep in a sand bed.

Scales

In a sense scales are a type of leaf cutting, for scales are simply rudimentary leaves. It is in the propagation of lilies that they are chiefly employed, but fritillarias and other bulbs formed of scales that lap each other like shingles on a roof, can also be grown from scales. In this method parent bulbs are dug as soon as they are through blooming, the thick outer scales are pulled off entire, without breaking their bases, and are planted at once, before they have any chance to dry, in a bed of just-moist peatmoss and sand or in sandy soil in a cold frame or in flats that are kept in a cellar or other dry place until the young bulbs have formed. Excessive wetness will cause loss by rotting.

The new bulbs will have developed nicely in from six weeks to three months and those planted in flats may then be set out in well-drained beds outdoors at a depth of about two inches. When winter comes they should be mulched heavily, the mulch being removed with the coming of spring.

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