This type of stem cutting is made from the mainly non-lignified, actively growing, soft growth (in the very early stages of the initiation of secondary thickening) of the current season’s extension. Because of the relatively elementary level of cell differentiation it has, generally, a high capacity to develop adventitious roots (as it inevitably has little de-differentiation to discard) – assuming that the plant has an acceptable level of inherent capacity to regenerate. However this advantage is balanced by the difficulty of maintaining the material in a viable and effective condition so that it can respond. This implies, especially because of the susceptibility to desiccation, that a sophisticated system of environmental control is required. In the UK, with its continuous variation in weather patterns, it is customary, for this purpose, to use an intermittent mist system or fogging unit. (see article - Mist Propagation)

 

1. Those deciduous woody plants which have an acceptable level of regenerative capacity will regenerate throughout the season when softwood material (usually tip growth) is available and this will root and establish quickly until quite late in the growing season eg:-

Abeliophyllum

Deutzia

Forsythia

Hydrangea

Philadelphus

Weigela

 

2. However the most difficult group to deal with are those genera which have a limited season of response from bud break until more or less this flush of growth declines (often as little as 4-6 weeks) and there is effectively no further flush of growth during the year – in practice this energy is diverted into flower and seed production. Thus there is only this limited window of opportunity - as capacity to regenerate vegetatively declines very quickly after this phase.

 

The practical and economic implications for cutting production determine that the stock plants are manipulated to develop the maximum number of suitable cuttings. The object is to produce shoots from lateral buds which are of an average caliper, as these develop the most satisfactory rooting response. This will involve pruning back the tips (which if left, tend to produce thick, stocky shoots - these tend to depress lateral growth and exhibit lower regenerative capacity). The operation should be conducted sufficiently early in the dormant season so that these lateral buds lose the influence of the apical dominance and will then break uniformly along the branches and grow at an even and comparable pace so that a maximum, uniform crop of cuttings is available.

 

The cuttings are collected as the spring flush of growth begins to decline and at this stage the base of the cutting is just beginning to lignify. The cuttings should be severed form the parent, flush with the previous season’s growth, so that the basal swelling is incorporated.

 

Generally these plants only develop the one flush of growth annually and the window of opportunity (ie when regenerative capacity is maintained) can be quite short (4 to 6 weeks for deciduous azaleas). The cuttings will be relatively small (short) – about 3-5 inches for the deciduous azalea.

 

These subjects are deciduous and often slow to root and establish physiologically - it is important, therefore, that, before the onset of dormancy, they develop as an ‘integrated’ plant in order to survive over the winter and emerge from dormancy satisfactorily in the Spring. This implies that the cutting develops shoot extension growth and that this is part of the overall pattern of normal growth so that the new plant is physiologically integrated. Thus it is capable of a normal autotrophic existence and can produce and store carbohydrate for overwinter survival.

 

Examples of this group of plants include:-

Deciduous Azaleas (Rhododendron)

Large Flowered Lilacs (Syringa)

Flowering Dogwoods (Cornus)

Fringe Trees (Chionanthus)

Japanese Maples (Acer)

Smoke Trees (Cotinus)

as well as:-

Corylus

Corylopsis

Hamamelis

Fothergilla

Parrotia

Pistacia

Stewartia

Styrax

Halesia

Deciduous Euonymus

Viburnum - Carlesii types

 

The incorporation of the basal swelling of the current season’s extension growth is a significant contributor to the success of this technique as it is this area of the stem which has developed a high level of regenerative capacity - largely because of its structure and the vigour and speed of its development.

 

Practically the most significant part of the propagation process is concerned with maintaining the turgidity and optimum water status of the material and this is important from the moment the cutting is severed from the parent. Thus the material is best collected when it is turgid, collected in small batches and processed quickly.

 

When the cuttings have been collected they require little or no further trimming unless basal leaves need to be removed in order to facilitate insertion into the rooting medium – this should be done with clean sharp cuts.

 

As these subjects are on the cusp of a satisfactory rooting potential, it is probable that they will benefit from the application of a suitable ‘hormone rooting material’ to enhance the rooting potential. This should be applied to the base of the cutting only and not dipped so that it coats the outside of the bottom of the cutting - as those concentrations needed for rooting are likely to inhibit root emergence through the side of the cutting.

 

Once treated and inserted into a relevant rooting medium they should be placed in, and subjected to, a relevant system of environmental control which will maintain a suitable water status, with adequate light to maintain photosynthetic activity at an advantageous level and an effective temperature regime which provides for root development and prevents excessive aerial stem growth until regeneration begins. Conventionally this is achieved in a mist propagation unit with bottom heating to maintain a temperature of 20̊C (the optimum economic level for root production in soft wood cuttings) – although fogging systems are also effective. It is relevant to ensure that the water application system is operating only at the required level as the often extended rooting period will cause leaching of the cuttings if the application is greater than that which achieves the desired effect.

 

The commonest problem, which is encountered, is that the cuttings, although producing roots, do not develop sufficient shoot growth, before the advent of dormancy inducing conditions, to create a physiologically integrated young plant and develop a sufficient carbohydrate store. It requires such a status in order to respond to the stimuli which will allow it to emerge from dormancy when conditions are suitable in the spring.

 

These dormancy inducing conditions (reducing day length and lowering temperatures) can be reached by early August for some species. Thus practically it may be necessary to extend the season of potential development by extending the day length, maintaining temperatures and ensuring high enough potash levels to ensure a response to the stimuli. The alternative is to extend the season forwards by growing the stock plants under protected conditions so that the shoot growth is produced earlier in the season and the rooted cutting has a longer natural season in which to establish.

 

3. Another significant group of woody plants, often with a limited pattern of capacity to regenerate root initials, which will respond to a similar process and regime, is the deciduous woody members of the Rosaceae.

 

The season of rooting capacity is not so critical to this group although in some cases, because of the lengthy period needed to achieve root production, the season is therefore confined to the early months as there is not the same spurt of spring growth and the season of capacity may well last through the season. There is, of course, considerable variation in the ability of the many species to regenerate.

 

Deciduous Rosaceae

The pome group are generally slowish to root and benefit from the early season propagation in order to give time for the production of a well established liner before the onset of dormancy:-

Amelanchier                 Aria

Aronia                      Cormus

Chaenomeles                 Sorbus

Crataegus                   Torminaria

Cydonia

Malus

Mespilus

Pyrus

 

That group which are best described as ‘Spiraea’ like are generally more easy to root and establish reasonably quickly and can thus be propagated in mid-season:-

Spiraea

Holoduscus

Neillia

Physocarpus

Sorbaria

Stephanandra

 

Generally the Plums, Peaches, Almonds, Cherries etc are slow and require the full season to establish:-

Prunus

also

Exochorda

Lyonothamnus