To increase a particular variety of bulb rapidly it is necessary to use artificial techniques, because the natural rate of increase, although steady, is generally slow.
Scaly bulbs, such as lilies and fritillaries, have relatively small, narrow scale leaves which can readily be pulled off the basal plate of the bulbs. When they can best be propagated depends on the availability of bulbs. Ideally, it is easier to deal with fresh bulbs, and these are normally available in October/November. Imported bulbs are not usually available until January/March, and these will invariably have wilted slightly, which makes them less than ideal as propagating material.
Take cuttings from a fresh bulb in a turgid condition by pressing the scale leaves outwards until they snap off close to the basal plate of the bulb. With a flaccid bulb, cut the scale leaves as close to the basal plate as possible, using a sharp knife.
To propagate from one bulb, cut off only a few scale leaves from the outside of the bulb. Some bulbs, for example lilies, do not like being lifted and replanted; therefore dig a hole around the bulb, break off some scales and replace the soil round the bulb.
Any scale leaves will carry potential rotting agents and so they must be protected. Place the scales in a polythene bag filled with a fungicidal powder such as Captan. Shake the bag vigorously until the scale leaves are completely covered with a thin film of fungicide.
Mix the scale leaves with four times their volume of an extending medium, which will allow them to develop in a damp, well-aerated environment. Various materials, such as damp vermiculite, can be used very successfully, but, provided that it is adequately sterile, a mixture of equal proportions of damp peat and grit is just as suitable. Place the mixture and a label in a polythene bag. Blow into the bag; when fully expanded, tie its neck. Store in a warm (21°C/70°F) place, such as an airing cupboard, so that new plantlets can develop.
The rate at which regeneration occurs is 'related chiefly to temperature, but is also a varietal characteristic—some being quicker to propagate than others. Generally activity may be expected in about six to eight, weeks.
The new plant will initially take the form of a bulblet and will develop on the broken surface at the base of the scale leaf.
4 Mix the scale leaves with four times their volume of damp peat and grit. Place in a polythene bag.
5 Place a label in the bag. Blow into it. Then tie round its neck. Store in an airing cupboard.
6 Remove the scale leaves from the polythene bag as soon as bulblets appear on the broken basal surfaces.
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As soon as these bulblets appear, remove the scale leaves from their bag and plant them vertically in John Innes No. 1 potting compost or equivalent (see page 12). They can either be planted singly in a 3-3-j in pot or lined out into a deep tray, depending on numbers. Ensure the tips of the scales are just visible above the compost. Cover with grit and label. Water sparingly. Keep the new plants in a warm (21°C/70°F), light environment. In early spring the bulblets will produce leaves above the compost. In summer, harden off the plants.
At the end of the season, when the leaves have died down, lift and separate the new young bulbs. Replant immediately.
1 Remove a scale leaf from the bulb by pressing it outwards or cutting it close to the basal plate.
2 Snap or cut off only a few more scale leaves from the outside of the bulb.
3 Place the scale leaves in a bag filled with a fungicidal powder. Close bag and shake vigorously.
7 Plant each scale leaf with its tip just visible. Cover with grit and label. Place in a warm, light area.
8 Harden off the plants in summer after the bulblets have produced leaves above the compost.
9 Separate new bulblets from their scale leaf once their leaves have died down. Replant and grow on.
Some tunicate bulbs, such as hyacinth, grow larger each year and propagate very slowly by natural division of the bulb. They therefore have to be propagated artificially if a significant increase in numbers is required.
The scale leaves of tunicate bulbs are large and encircle the bulb; they are not as readily removed from the basal plate as the leaves of scaly bulbs. It is therefore necessary to leave their cut scale leaves in situ while inducing them to produce plantlets. There are two ways of doing this: scooping and scoring.
This is carried out towards the end of the bulb's dormant season. To scoop the bulb successfully, and with minimum damage, requires a special tool: an old teaspoon with one sharpened edge is excellent. Use it to cut out the basal plate in one scooping movement, leaving the rest of the bulb undisturbed and the cut surfaces of all the scale leaves exposed. Although it is possible to do this with a knife, it is inadvisable as the centre of the bulb may become macerated knd subject to rotting. Once the basal plate has been removed, dust the cut scale leaf surfaces liberally with a fungicidal powder to minimize potential rotting.
Set the bulb upside down, with the scale leaf bases exposed, on a wire tray or in a tray containing dry sand. Place in a temperature of at least 2TC/70"F to encourage calluses to form on the scale leaf bases and so further combat any chance of infection. At the same time, the bulb should be kept as dry as possible, but ensure that the scale leaves do not desiccate. An airing cupboard is probably a suitable environment, but dampen the sand occasionally.
In about two to three months the new bulblets will develop on the cut surfaces of the scale leaves. Plant the bulb in a pot, still placing it upside down so that the bulblets are just below the surface of the compost. Label clearly. Harden off and then leave in a cold frame.
In spring, the bulblets will grow and produce leaves and the old bulb will gradually disintegrate. At the end of the season lift and separate the bulblets, and replant. They will normally take a further three or four years before flowering size is reached.
Flowering bulbs can be produced in a shorter time by using a similar technique called scoring, which makes fewer, larger bulblets as there are less cut scale leaf surfaces.
3 Dust the cut scale leaf surface with a fungicide. Set upside down on a tray.
The process follows exactly the same pattern as for scooping except that, instead of cutting away the basal plate of the bulb, the basal plate is scored with a sharp knife. Cut through the basal plate of a tunicate bulb until the scale leaves are scored to a depth of about \ in. Make four equally spaced scores if the bulb is large; on smaller bulbs two scores at right angles will suffice.
Then place the scored bulb in a warm (21°C/70°F), dry environment for a day; this will cause the cuts to open out. Dust the cut surface with a fungicide such as Captan. Subsequently, the treatment is the same as for scooped bulbs.
The bulblets produced in this way usually only require a further two or three years to reach flowering size.
1 Make two scores at right angles to each other on the basal plate of the bulb.
2 Place in a warm, dry area until the bulb case opens out. Dust with fungicide.
3 Place on a tray. Store in an airing cupboard until the bulblets develop.
Growing on bulblets
Growing on bulblets
4 Store in the airing cupboard until bulblets appear on the cut surfaces.
5 Plant the bulb upside down with the bulblets just below the compost surface.
6 Lift and separate the bulblets at the end of the season. Replant at once.
Herbaceous plants with fibrous crowns
Herbaceous plants with fibrous crowns
1 Lift the plant that is to be divided directly after it has flowered.
2 Shake off as much soil as possible.
3 Wash the crown and its roots in a bucket, or hose it clean.
4 Shorten all tall stems above the ground to minimize water loss.
5 Break off a piece with at least one good "eye" from the edge of the crown.
6 Divide any intractable pieces with an old carving knife or similar blade.
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Dividing a plant is a common way to propagate many herbaceous perennials, and it is also used to rejuvenate favourite plants and keep them in a vigorous condition. Propagation by division is also successful with shrubs, such as sumach, that produce suckers; with semi-woody perennials, such as New Zealand flax, that produce a crown of offset shoots; and with most plants with modified stems, such as bearded iris (see pages 42-9).
The commonest method of propagating plants by division is that used for herbaceous perennials, such as chrysanthemums, with fibrous roots and a relatively loose crown. Normally, the central part of the crown becomes woody over the course of two or three years. As this woody area does not produce many shoots and generally loses vigour, it is discarded and the remainder of the clump is divided into suitable-sized portions for planting out and re-establishing a new crown.
The only variable feature of this form of propagation is the time at which division is carried out. As a general rule, the most opportune time to divide such plants is directly after flowering, as this is when the new vegetative shoots are being produced and the new root system is developing. In very late-flowering subjects, this would be the following spring.
Lift the parent plant and shake off as much soil as possible. Then wash the crown in a bucket, or hose it clean of any residual soil. The plant can be divided without this pre liminary preparation, but it is much easier to deal with clean plants, especially if the soil is wet and muddy. Shorten any tall stems above the ground to prevent unnecessary watei loss, especially if the division takes place in summer. Break off a piece with at least one good "eye" from the periphery of the crown, where the young shoots are generally pro duced; avoid the central woody crown, which is of no value and should be discarded. If the piece proves rather intractable to remove, cut it off, using an old carving knife or similar blade. Plant out the new clump as quickly as possible to the same depth as it was growing previously. When, replanted it should be labelled and watered in—indeed "puddled' in would be more appropriate.
7 Make a hole and replant the new clump at once. Firm the soil and label.
8 Water very thoroughly, using a watering can with a spray attachment.
9 Keep the new clump free of weeds.
Herbaceous plants with fleshy crowns
Many herbaceous plants, such as hostas, develop a compact, fleshy crown that is not easy to pull apart.
The best way to propagate these plants is by division towards the end of their dormant season, when buds will begin to shoot, indicating the most vigorous areas.
Lift the parent plant and shake off as much soil as possible. Wash the crown thoroughly. With a convenient-sized knife, cut the crown into pieces. The size of divisions will depend on preference, but must include at least one developed shoot. Avoid latent buds, which do not always develop satisfactorily. Dust the cut surfaces with fungicidal powder to reduce the chances of fungal rots. Do not allow the divisions, especially from really fleshy rooted plants such as hostas, to dry excessively. Therefore replant the divisions either in the ground or in a pot as quickly as is feasible. Label them clearly.
Naturally dividing alpines
There are a number of alpine plants, such as campanulas, which lend themselves to propagation by division because their crowns
Herbaceous plants with fleshy crowns
1 Lift the plant to be divided towards the end of its dormant seasop.
separate naturally into individual new plant-lets each season.
After flowering, or in the spring if the plant flowers in the autumn, as does Gentiana sino-ornata, lift the plant and tease apart the divisions. Replant as soon as possible. Label and water in well.
This is a very simple but effective system of increasing plants. If the crowns are lifted and divided fairly frequently the rate of increase can be quite dramatic. However, plants left in situ for a long period tend to produce only a few large divisions.
Some perennials with upright, sword-like leaves, for example Phormium, increase in size by producing a sort of offset that develops into a large crown of individual shoots, each with its own root system.
To propagate these plants, it is best to divide them in the spring, although it can be done at any time of the year. Lift them and shake out the soil, if necessary hosing or washing the crown clean. Pull the various pieces apart. Cut the clump with a spade or hatchet if it is hard and woody in the middle,
2 Wash the crown well. Cut off a piece with at least one developed bud.
3 Dust the cut surfaces with a fungicidal powder. Then replant immediately.
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and replant the divisions fairly quickly to avoid the roots drying.
There are a few woody shrubs, such as blackthorn, that produce suckers, which then develop into individual clumps of stems. Lift these plants in the dormant season and wash thoroughly. Divide the clump of stems into convenient-sized portions. Normally the main core of the clump will be woody and will carry few roots. This will be of little value for propagation purposes, so take the new pieces from the younger, more vigorous growth on the outside of the clump.
Cut back the branches fairly drastically to reduce water loss, as the buds will break in the spring before sufficient roots have been' produced. Replant the divisions back in the ground as soon as possible and label.
Lift relatively isolated suckers individually in the dormant season and use to establish new plants.
If the plant has been grafted—as may happen with Japanese quinces—then it is the rootstock, not the cultivated variety, that is divided.
Woody shrubs with suckers
Plants, such as Michaelmas daisies, that produce particularly loose crowns can be propagated by separating off single stems on the periphery of the crown so that each has an adventitious root system. These single stem portions are described as "Irishman's cuttings", and they should be planted at once.
1 Remove isolated suckers from woody shrubs during the dormant season.
2 Cut back part of the roots and top growth.
3 Replant immediately; label and water in well.
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