Plant Propagation

There are few more satisfying pastimes for the keen amateur gardener than the various forms of plant propagation. Whether raising plants from seed, rooting cuttings, layering plants or increasing them from offsets there is much to interest the enthusiast.

PLANTS FROM SEED

Seed sowing is, for the amateur gardener, the most popular form of plant increase. Most sowing is done between February and May and warmth, moisture and air are essential ingredients of success. This pre-supposes the use of a suitable compost such as the John Innes Seed Compost, one of the soilless seed mixtures, or. In special cases, a mixture made up to meet the particular needs of an individual plant. Most plants, however, are perfectly happy with standardised composts and this is an appropriate place to acknowledge what a boon these are to the present-day gardener. They have made plant cultivation much easier by simplifying one of the most important working procedures.

Temperatures

Some seeds need much higher temperatures than others to germinate successfully, for example, begonias need a temperature of 18 to 21° C. (65 to 70° F.) and tomatoes 16 to 18° C. (60 to 65 F.) while some other plants, including many annuals grown under glass require a temperature as low as 4° C. (40° F.).

For seed sowing within the greenhouse a propagating frame which can be kept at a higher temperature than the rest of the house is. I consider, essential. It is also very efficient for such a frame, heated electrically and thermostatically controlled. Can provide regulated conditions within very line limits and there is a big saving on the fuel bill if only a small area of the house is heated to the required temperature. It is often important for another reason, for high temperatures may be damaging to other plants which one may wish to grow.

Seed Sowing

Seeds can be sown in wooden seed boxes, clay flower pots, half-pots or seed pans and plastic pots or seed trays. Whichever container is used it must be scrupulously clean if trouble from diseases is to be avoided. If clay pots or seed pans are used, pieces of broken flower pot or crocks, as they are called, should be placed in the bottom to ensure good drainage, and boxes should have an open slit along the bottom to allow surplus water to drain away freely. This slit, like the holes in the flower pot. Should be covered with pieces of crock to prevent the soil washing through. Plastic containers – and more and more of these lightweight, easily cleaned and easily stored receptacles are being used nowadays – are well supplied with small drainage holes and it is not necessary to use crocks to help drainage.

The container will now be filled with compost, and if a soilless mixture is chosen this should not be made quite so firm as if the John Innes mixture is used. Do the firming with a wooden ‘presser’ – a flat piece of wood to which a handle is attached. This useful tool can easily be made at home. The surface of the compost should not be too fine or it may form an unwelcome ‘pan’. A compost passed through a 3/8-in. sieve would be ideal, even in the case of very small seeds.

It is always best to water the compost an hour or so before seed sowing so that any surplus moisture has time to drain away, leaving the compost in an ideal condition. This watering may be done by immersing the receptacle almost to the rim in clean water until the moisture is seen to seep through to the surface. Alternatively, the compost can be watered carefully from overhead, using a watering-can fitted with a fine rose.

It is a cardinal rule when sowing seed to spread it out as thinly and evenly as possible. Small seeds should be sprinkled over the surface and large seeds positioned with the ringers. In the case of small seeds like those of begonias and lobelias, no covering of compost is needed. Instead, a small sprinkling of fine sand gives sufficient cover. Some gardeners like to just press the seeds into the compost with a wooden presser such as I have already referred to. Slightly larger seeds should be little more than hidden under a layer of compost (tomato seed, for instance, needs a covering of about 1/8 in.) and larger seeds should be about 1/4 in. under the surface. There is rarely any need to sow more deeply than this.

Label each pot or box immediately with the name of the plant, and, for good measure, the date of sowing. Then place a sheet of glass or polythene over the container, cover this in turn with paper and place in the required temperature.

The coverings will cut down the loss of moisture from the soil and in many cases watering will not be necessary until the seeds have germinated. As soon as germination takes place the coverings must be removed and the seedlings exposed to full light, but not hot sunshine. If this uncovering is left too long the seedlings will become weak and drawn and more open to attack by disease.

Damping off disease is a constant hazard to seedlings, causing decay at the base of the stem and the collapse of the plants. The use of partially sterilised loam when preparing the seed compost and the avoidance of damp, stuffy conditions will go a long way towards ensuring freedom from this disease.

Pricking Out Seedlings

Seedlings of plants like begonias, gloxinias, streptocarpus and lobelia, which inevitably must be very close together, should be pricked off as soon as they can be handled safely. Such seedlings are too small to separate with the fingers alone without damage and a pointed stick or small label with a V cut in the end is a valuable aid in this respect as it can be used as a lever to ease the seedlings from the compost.

PLANTS FROM CUTTINGS

Cuttings fall into several categories – hard-wood, half-ripe, soft-wood, leaf and root cuttings, leaf bud cuttings, stem cuttings and vine eyes – and these allow the gardener to obtain exact replicas of existing stock of an enormous range of valuable garden and greenhouse plants. Popular greenhouse plants raised in this way include Zonal and Regal pelargoniums, Chrysanthemums, carnations, winter-flowering and double begonias, poinsettias, dieffenbachias and such shrubs as fuchsias, camellias and Plumbago capensis.

Success with half-ripe and soft-wood cuttings depends, to a large extent, on keeping the atmosphere suitably moist and close to prevent flagging. (Hard-wood cuttings are much tougher and are usually rooted in the open or in a cold frame, except in the case of tender woody subjects.) Shading from the sun, the use of an open, sandy rooting medium to encourage root formation (pure sand can also be used if the cuttings are provided with a growing compost as soon as roots form) and the use. Whenever this is considered necessary, of hormone rooting powder are other ingredients of success with this form of propagation.

Cutting Composts and Containers

Good rooting mediums consist of equal parts loam, peat and sand; equal parts sand and peat; Vermiculite: and seed sowing compost. Pots or boxes can be used as receptacles. If pots are used it will be found that the cuttings will root more readily if they are inserted around the edge of the pots. The number which can be accommodated in one pot will depend on the size of the cuttings and the pots used; these are usually of 3- or 3-½-in. size. Always make sure that the cutting rests firmly on the bottom of the hole made for it: if an air space is left below the cutting any roots which form will wither and die.

Hard-wood Cuttings

Cuttings of this type are made in autumn from the firm, well-ripened current year’s wood of trees and shrubs. I usually do this job in November. These cuttings are often rooted in the open garden but some are rooted in cold frames from which the lights are removed. This gives slightly tender subjects the little protection they need.

Some are best taken with a heel of older wood attached and these are referred to as heel-cuttings. A small sideshoot is pulled away from the parent plant for this purpose. It can be up to I in. thick but all weak, spindly shoots should be rejected. The bark which forms the heel of the shoot is trimmed smooth with a sharp knife and the other end is tipped just above a bed to leave a cutting 9 to 10 in. in length. The lower leaves are removed at this time. If the cuttings are taken without a heel, cut them through cleanly at the lower end just below a leaf joint.

The base of each cutting should now be dipped in water and then in hormone rooting powder before planting in the frame. Plant the cuttings in rows 2 in. apart with 2 in. between the cuttings in the rows. About one third of the cutting should be below soil level after planting with a wooden dibber and the rooting medium should be light and well drained.

Rooting with this type of cutting is slow and little can be expected to start happening until the following spring. The rooted cuttings should not be moved to a nursery bed until the following autumn.

Half-ripe Cuttings

A wide range of shrubs, including those splendid greenhouse plants camellias, fuchsias and pelargoniums, as well as many other popular plants like nepeta (catmint), potentilla and spiraea are raised from half-ripe cuttings taken in July, August or September from shoots made during the current season which have not fully hardened. Wood which is too immature or soft must be avoided. Neither too hard nor too soft should be the rule.

Where possible I advise taking such cuttings with a heel of the older wood attached. Most will be quite small, not much more than 4 to 6 in. and some, like the heathers, only 1 to 2 in. long. If the tip of the shoot is soft this is best removed and cuttings taken without a heel are cut off cleanly with a sharp knife just below a node. The leaves should be removed from the lower part of the cuttings, otherwise they are likely to rot off in the rooting medium and cause infection.

The prepared cuttings can be rooted in a cold frame, or under a cloche with its ends sealed with glass panes. Alternatively, they can be placed in a propagating frame in the greenhouse. This will give the quickest results, especially if bottom heat is provided. Another good method with small numbers of such cuttings is to root them in pots – with the cuttings placed round the edge as recommended earlier -these being individually enclosed in polythene bags. They are then placed on the greenhouse staging to root. Again, dipping the base of the cuttings in water and then in hormone rooting powder before insertion much increases the chances of rapid rooting.

Set the cuttings 2 in. apart and make the planting holes with a wooden dibber. Make quite sure that the cutting sits firmly on the base of the hole, as I have already described.

Water immediately after planting and keep the atmosphere moist and close. Shading should be provided against strong sunshine. If the cuttings are being rooted in a cold frame they should be kept closed for three to four weeks with the cuttings being given a daily syringing for the first week or so. The frame light should be lifted for a very short time each morning (a few minutes) to allow the condensation to run off the inside of the glass. After a month, rooting should be well under way and ventilation should be gradually increased. The young plants which result will stay where they are during the winter – with protection from a frame light during severe weather – and be planted out in nursery rows the following spring. By the autumn they will be ready for permanent planting.

Greenhouse-raised half-ripe cuttings which have been assisted to root by the provision of heat will have to be hardened off gradually, the resulting plants going through acclimatisation stages in a cool greenhouse and cold frame before being subjected to normal outdoor conditions.

Soft-wood Cuttings

These are cuttings made from young shoots of the current season’s growth and they are usually rooted in spring in a temperature of 13°C. (55° F.) or more. A large number of plants are raised in this way from chrysanthemums and dahlias to begonias, violas and salvias, to mention but a few.

Shoots of 2 to 3 in. in length are chosen for this purpose and they are trimmed off cleanly below a leaf joint with a sharp knife or razor blade. The lower leaves should be removed. When necessary, the cutting can be dipped in hormone rooting powder before insertion to make successful root formation more likely. The cuttings can be rooted in pots or boxes filled with sand or Vermiculite or a mixture of loam, peat and sand, afterwards being placed in a warm propagating frame on the greenhouse bench. Alternatively, the cuttings can be inserted directly in the compost of a propagating frame. (The cuttings which are rooted in pure sand or Vermiculite must be moved into a good growing medium as soon as they have formed useful root systems.) As with other cuttings, shade must be provided against strong sunshine and all must be potted on without undue delay whatever the mixture is in which they are rooted.

Leaf Bud Cuttings

Some plants, including those popular greenhouse shrubs the varieties of Camellia japonica, can be raised from leaf bud cuttings made from half-ripe wood. The cuttings consist of a small piece of stem, together with a leaf and the growth bud which is found in the axil of the leaf. They are inserted like ordinary stem cuttings in a propagating frame.

Leaf Cuttings

Many greenhouse plants can be grown from leaf cuttings, including streptocarpus, Begonia rex, gloxinias, Saintpaulias, Peperomias and sansevierias. Mature leaves must always be chosen for this form of propagation. In the case of Begonia rex it is only necessary to cut through the larger veins on the under-surface of the leaf with a sharp knife. The leaf is then laid flat on the compost (a mixture of peat and sand) in a well-drained pan or box. Small stones or pebbles placed on the leaf will keep it in close contact with the compost. The container is then placed in a warm propagating frame. Young plants will develop at each point where the veins were cut. One leaf could produce as many as twenty plants.

An alternative is to cut up the leaves of Begonia rex into small squares, each piece with a main vein running through it. And root these in the same way as already described for the other method.

In the case of peperomias, gloxinias, Streptocarpus and saintpaulias, the leaves are pressed into the compost, stem end first, and the veins are not cut. The sansevieria, with long, strap-like leaves, can be rooted from pieces of leaf cut up into 3-in. long strips and inserted in the compost of a warm propagating frame. But take note that many variegated plants. Including sansevierias and peperomias (with the exception of P. sandersii) will not come true to type from leaf cuttings. The sansevieria, for example, loses the yellow band along its leaves and the peperomias, with the exception of the one mentioned previously, lose the variegation on their leaves.

Propagation from leaf cuttings is, in my opinion, fascinating, and it is a form of plant increase 1 am sure many gardeners find especially enjoyable.

Stem Cuttings

Another method of propagation. Useful with a few plants like dieffenbachias and draceanas. Is by stem cuttings. Using a sharp knife, the stem is cut up into short sections. 1 to 3 in. long and including at least one dormant bud. They are rooted by placing them horizontally in sand in a warm, moist propagating frame. When rooting is well under way, they should be potted up separately in John Innes No. 1 Potting Compost. This can be anticipated when signs of sprouting from the previously dormant bud are evident.

Root Cuttings

Many plants can be in-creased from root cuttings, the majority of them perennials with thick roots like anchusa, oriental poppies and verbascums, but also others with fibrous roots like gaillardias and the border phlox which has thin, wiry roots. Dracaena is a greenhouse plant which can be propagated in this way. Small portions of root, an inch or so long, are prepared by cutting their top ends straight across and their bottom ends on the slant, this to avoid the possibility of their being planted upside-down. The prepared cuttings are inserted upright in the growing medium, using a blunt-ended dibber. A few types of root cuttings, such as phlox, are laid flat on the compost and in such cases it is not necessary to distinguish between the top and the bottom.

The cuttings are raised in seed boxes filled with a seed sowing compost or a mixture such as is used for rooting stem cuttings. The cuttings should be just covered with compost and be placed in an unheated frame or greenhouse for rooting and growing on. The compost should be kept just moist at this stage. When the cuttings – or young plants as they now are – start to make growth they should be potted individually into small pots or replanted in boxes, using a suitable compost.

OTHER METHODS OF PLANT PROPAGATION

Offsets

Numerous plants, particularly bulbs and corms, but also other plants which produce several crowns, can easily be divided to make new plants. These are exact replicas of the parent. They are removed with their roots intact and are potted up separately to develop as individual plants. Cryptanthuses and gloriosas are examples of greenhouse plants which can be readily increased in this manner.

Layering

Ordinary layering, when growths are pegged down in a free-draining, light compost mixture to root at leaf joints and form new plants, is not a common method of increase in the greenhouse. But it is used to increase plants such as the lovely greenhouse climbers Hoya carnosa and Lapageria rosea. Selected strong growths are pegged down at a leaf joint into small pots filled with John Innes No. 1 Potting Compost to root and form new plants. Sometimes, one or two leaves are removed to make it easier to secure the stem in the compost. Layering is done in spring or summer and when rooting has taken place the new plants are severed from the parent plant and potted on as necessary.

Air Layering

This useful technique has been fully described in connection with ficus and reference is also made to it in the description of codiaeum cultivation, so there is no need to repeat the details here. It is another quiver in the bow of the greenhouse propagator which should be made good use of when opportunities arise.

Runners

A variation on ordinary layering is propagation from runners which some ornamental plants like Saxifraga sarmentosa (Mother of Thousands) form in the same way as strawberries. The plantlets which form on the runners are pegged down singly in 3-in. pots of loam, peat and sand, or John Innes No. 1 Potting Compost, and severed from the parent plant when they have rooted. Scales. A method of propagation used in connection with lilies is increase from scales, which are removed from the bulbs. This is done in early autumn. They are inserted upright in a seed box filled with a mixture of peat and sand and covered to a depth of 1/2 in. with a similar mixture. They are then moved to a cold frame and by the following autumn bulblets will have formed at the base of the scales. These are removed and potted up or planted out in a nursery bed.

Division

Simple division of mature plants which have become too large or are losing vitality is a form of increase adopted with numerous greenhouse plants including arums, ferns, marantas and orchids. The plants are taken from their pots and the old compost removed before dividing each one with a sharp knife or separating it carefully with the fingers. The separate pieces are then repotted in good compost and grown on as usual. This is a job best done in spring when growth is getting under way. Re-establishment is quickest at this time and the plants have everything in their favour.

Tuberous begonias bear buds on their tubers and these can be divided to make new plants after growth has started. Dahlias, which can be started into growth in a greenhouse with a temperature of 16°C. (60°F.), do not have buds on the tubers themselves but at the base of the old stems. If these are to be divided it is essential that each division includes a piece of the old stem with at least one bud attached. By starting the tubers into growth in this way it is possible to be certain that each division has one or more buds attached. The tubers are boxed during April in a mixture of peat and sand or peat alone. They are divided immediately before planting them in the garden at the end of May or early June when there is no longer any danger of frost occurring. Dahlias can be increased in this way if one does not have a green-house but with this facility success is more assured.

Vine Eyes

Grape vines are increased by means of ‘eyes’ which are the dormant growth buds removed from well-ripened sideshoots in autumn with a small portion of stem attached. These bud cuttings will be about 1-1/2 in. long when prepared. With the bud in the middle. They are placed horizontally and bud uppermost on the surface of a sandy compost, either one to a small pot or several to a larger one. They are given little or no covering. But some gardeners like to peg them down with pieces of bent wire to obtain really firm contact with the compost. The pots are then placed in a propagating frame with a temperature of 18° C. (65° F.) for the eyes to root and form new plants. When this occurs, they should be potted up in the normal way, using John Innes No. 1 Potting Compost.

MIST PROPAGATION

The technique of mist propagation is now very widely used and has certainly lightened the load of the propagator in addition to making the increase from cuttings of some notoriously difficult shrubs very much easier.

Like so many successful items of equipment. A mist propagation unit is basically very simple. It consists of a spray unit, or units, which are automatically operated and have the function of keeping the leaves of cuttings inserted underneath their coverage permanently moist. This is achieved in various ways, but the one most often adopted is by using what is called an ‘electronic leaf which is set amongst the cuttings. When it becomes dry an electrical relay is set in motion which operates the water supply and the spray nozzle ejects a fine mist until the electronic leaf’s surface is again saturated. The cuttings are. Therefore, never left dry and flagging will not occur. It is, of course, heavy moisture losses through the leaf surfaces which are in normal circumstances difficult for the home gardener to counteract. In sunny weather the cuttings would need repeated syringing, which is not generally a practical proposition.

The cuttings, prepared in the normal way, are inserted in a bed of sand heated by soil-warming cables. Half-ripe cuttings will normally have formed roots within three weeks of insertion. Also, large-leaved evergreen shrubs which are difficult to propagate in other ways present no difficulties when raised under mist.

Once rooted, the cuttings are potted singly in a suitable growing medium and are put back under the mist for ten days or so to become gradually acclimatised to ordinary greenhouse conditions.

01. March 2012 by admin
Categories: Featured, Greenhouse Gardening | Tags: , , , , , | Comments Off on Plant Propagation

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