Commercial Marcotting of Fruit Trees by Peter J. Young
Marcotting is the recognised international horticultural term for aerial layering originating from the French word ‘marcotte’ that means ‘to aerial layer. This method of vegetative propagation is widely used throughout the world to clonally propagate fruit trees that are very difficult to reproduce by any other means, e.g. Lychee and Longan. It is also an easy way to successfully propagate most types of plants without the need for specialised equipment, growing houses or skills. Marcotting is commonly used in Asia for the propagation of most fruit trees in particular Citrus, Fig and Mango and also many ornamentals such as Hibiscus, Rose, ‘Casuarina and Syzygium. Such marcotted branches are often sold as marcots at markets or through retail outlets with fruit and/or flowers attached alleviating the need for Labels.
Marcotting does use up large amounts of propagation material and is labour intensive. Both these factors limit the commercial use of this propagation technique when compared to conventional methods in highly competitive nursery industries. It can also produce a weak rooted plant that is prone to lodging if the root system is not properly trained when the marcot is removed from the parent tree and grown on.
The basic principle is to cincture the branch by completely removing a section of bark right around the branch to a width of 1-4 cm depending on branch diameter. A suitable rooting media is placed over the cinctured area and enclosed in an impervious material that will retain the desired moisture level in the rooting media and keep excess moisture out. Usually sterile peatmoss is used as the rooting media and clear plastic is used as the impervious material. The plastic is held firmly in place by binding with strong twine or by using plastic covered wire, such as twist-ties. The marcot rootball needs to be held firmly in place during the rooting period as any twisting of the rooting media around the branch will damage roots.
Cincturing the branch removes the bark and hence the phloem or food conducting tissue down to the active cambium layer. Care must be taken not to excessively damage the water conducting tissue or xylem inside the cortex or the hard woody section of the branch. The stronger the cortex or woody section, the easier it is to cincture a branch without damaging the xylem or water conducting tissue. This is important as the branch stem and leaves above the cincture rely on this water supply for survival.
Plant food manufactured by the leaves above the cincture can no longer transfer down the branch to the lower stem and roots and accumulates in the cinctured branch. This accumulation of food reserves is as important as root development as it is this food reserve that supports the marcotted branch once removed from the tree until an independent root system develops.
It is important that no active cambium cells or any bark remnants are allowed to remain within the cinctured area. Re-callusing of the cincture will result in food reserves going back into the main parent plant and even if adequate roots develop in the marcot rootball, the marcot can die soon after removal from parent tree due to lack of food reserves.
Starches and carbohydrates begin to accumulate at the top of the cincture. This encourages the development of a ring of callous at that point and provided moisture conditions and rooting media are correct, roots develop from this callous into the rooting media.
The first roots that appear are generally thick, corky, adventitious roots that are few in number and very fragile. In time, fibrous secondary roots develop from the primary roots. It is important that marcots are allowed to remain on the parent tree until secondary roots are well developed. This will vary depending on plant genus, species, variety and temperature. Usually a minimum of 10 weeks to maximum 20 weeks is required for proper root development and sufficient food reserve accumulation.
MARCOTTING PROCEDURE Cincturing
The width of the cincture is generally 3-4 times wider than the branch diameter. A pair of adjustable pliers or multi grips are ideal for bark removal. Some species with very active cambium that tends to re-callous during the rooting period, need to be left for 1-2 weeks prior to wrapping with rooting media. Alternatively the cambium can be removed by scraping or by using abrasive emery paper. Angular stems can be a problem as bark with associated cambium may remain in grooves. Remove bark using a pointed instrument. Cincturing is best done when there is good sap flow as bark is easier to remove.
Rooting Media Type/Placement
Many different media may be used such as peatmoss, vermiculite, perlite, bagasse, leaf mould, clay and straw, well drained soil, coconut dust, rice hulls and raw sphagnum moss. Any media that is well aerated but holds moisture is suitable. Generally, peatmoss or raw sphagnum moss mixed with varying amounts of vermiculite or peatmoss is used to obtain the correct physical properties for each particular plant species. Sterile disease free materials give best results. A rooting media that holds together is easier to use as less is lost during the plastic wrapping procedure.
Rootball size should be as small as possible relative to branch size to achieve success, e.g. a completed rootball of 12 cm x 8 cm is ideal when marcotting Lychee and Longan branches 1-2 cm in diameter with a total marcot branch length of 50-60 cm. Too large a rootball will hold excess moisture that will inhibit root development and increase the weight on the parent tree that can cause limb breakage.
The placement of the rooting media is important. Aim to have the top of the cinctured area in the top one-third of the rooting media. This allows for some flexibility when wrapping rooting media onto branch. Too low and the roots will not develop as the top tie will prevent root development. Too high and the roots will not have sufficient room to grow.
Wrapping Methods The methods of ‘putting on the rooting media, plastic wrapping and securing vary greatly depending on personal preference and speed of operation required.
1. Plastic sleeve – suitable for small numbers as this method is slow. The required size plastic sleeve is pulled down over top of branch, tied off below cincture, rooting media placed into sleeve, plastic sleeve is pulled up, media squeezed tight and plastic sleeves tied off above cincture. Approx. 25 per hour/200 per 8 hour day.
2. Split pre-filled plastic pouch and flap – lower pouch is filled with rooting media, pouch is placed around cincture, rooting media is pushed up and around branch. Remaining plastic flap is wrapped around branch and fixed top and bottom using twist-ties. Approx. 45 per hour/350 per 8 hour day.
3. Pre-filled plastic bags tied off with 30-60 cm twine – plastic bags 20×10 cm are pre-filled and the open end tied off with 60 cm of strong twine. The plastic bag is cut from twine knot along one side and down to bottom. Push rooting media up around branch, pull plastic either side of branch over and around rooting media. Tie up using attached twine. Approx. 50 per hour/400 per 8 hour day
4. Jiffy 7 peat pot/alfoil wrap for mini marcots – Jiffy 7 peat pots are expanded in water and allowed to free drain. Cut attached net lengthways along one side of Jiffy 7. Push peatmoss around branch wrap with pre-cut alfoil sheet – suitable for very small branches around 0.5 cm only. Limited use – generally when propagation material is scarce.
TIME TO MARCOT
Marcotting can be carried out at any time of year so long as the bark is easily removed during the cincturing operation. Late spring-early summer is the best time provided mother plants are well grown and under irrigation if dry weather conditions are experienced at dust time of year. Best root development occurs under diurnal temperature range 15-28 C depending on plant species. Ideally if marcots can be removed and grown on during the warmer summer months, root establishment is easier and plants are established before the onset of cool winter temperatures. If dry springs and early summers are likely or if parent trees are not irrigated, it may be best to delay marcotting until mid summer or when rainfall is likely. Excessive rain with extended periods of cloudy weather and low temperatures’ generally gives poor results. The physical properties of the rooting media and thickness of plastic used may need to vary according to associated weather conditions experienced relative to time of year.
When removing mature marcots with very dry rooting media, place in water within 5-10 minutes of removal to avoid stress and possible root damage. Trim leaves on marcot branch according to extent of root system development. Trim any twisted roots and roots growing around and upwards before potting on. Keep newly potted plant in high humidity atmosphere of at least 75-¬80% R.H. Avoid excessive watering of newly planted marcot but do not let potting media and/or marcot rootball to dry out.
Care must be taken with fertilisers and any applied nutrients during initial establishment period. Weak nutrient solutions or small amounts of longer term slow release fertilisers are safest for 3-4 months. Well developed soil roots take 3-6 months to develop depending on plant species and temperature.