Plant Propagation - Layering
Layering is a form of rooted cutting in which adventitious roots are produced on a stem while it is still attached to the plant. The rooted stem (layering) is then separated and transplanted, while it later becomes a separate plant on its own roots. It is a natural means of propagation in blackberry or it can be induced artificially in many plants such as the clonal rootstocks of apple. In general, better rooting in layering can be achieved by ringing or wounding, etiolation, or the use of rooting hormones such as IBA, NAA, and providing favorable environmental conditions (temperature and humidity).
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- It is an effective method of propagation of species that generally do not produce roots easily by cuttings, such as mango, lychee, filbert, and kumquat, etc.
- This is a natural method of reproduction in blackberries and raspberries.
- Unlike other methods of propagation, it does not require precise control of water, relative humidity, or temperature.
- It is easy and does not require much infrastructure.
- Expensive in areas where labor availability is a problem.
- A limited number of plants can be produced.
- Plants produced by layering usually have short brittle roots.
- Mortality is especially high in air-layer plants.
Types of layering
The most commonly used layering systems for plants propagation include:
A. Ground Layering
- Simple Layering
- Compound/ serpentine Layering
- Continuous/Trench Layering
- Tip Layering
- Mound/ Stool Layering
B. Air layering
Of these, the most commercially important are mound layering for multiplication of rootstocks and air layering for some tropical fruits.
A. Ground Layering
Simple layering involves bending an intact shoot to the ground, forming adventitious roots. This method can be used for propagation in a wide range of plants, indoor or outdoor shrubs that produce more suckers. Layering is usually done in early spring using the plant’s flexible, dormant, one-year-old branches that can be easily bent to the ground. These branches are bent and 15 to 20 cm from the tip “down” in a “U” shape. bending, twisting, cutting, or girdling at the bottom of a branch bent into a “U” shape stimulates the roots at that location. The base of the layering is covered with soil or other rooting media, leaving the tip exposed.
Compound or Serpentine Layering
It is a modification of simple layering in which the one-year-old branch is alternately covered and exposed along its length. The ring-shaped bark is removed from the underground part of the stem. However, there must be at least one bud in the open part of the stem for the new branch to develop. After the roots emerge, the branch is cut into pieces and planted in the field. In this way, many new plants can be formed from one branch. It is also an easy plant propagation method, but only suitable for plants that produce thin, long, and flexible branches. Muscadine grapes are commercially propagated by this method.
Continuous or Trench Layering
It is the most common method of propagation for woody plants that produce long branches, and plants that cannot be propagated by other propagation methods. The vigorous rootstocks of apples such as M-16, M-25, and walnuts can be easily propagated by trench layering. With this method, it is important to plant the plants in a permanent row to propagate.
In this method, the plants are planted in rows at an angle of 450 to 90 cm at the base of the trench. The long and flexible stems of these plants are bent towards the ground and buried in the trench. Young twigs/shoots arising from these plants are gradually mounded in a mound of 15-20 cm high in autumn, winter, or the end of the growing season, depending on the species to be propagated. Then after rooting on these twigs/shoots, they are separated from the parent plant and planted in the nursery.
This is the simplest form of layering, which often occurs naturally. The ends of the twigs are buried 5 to 10 cm deep in the soil. The buried shoots develop roots within a month. New plants (layers) can be detached and transplanted into the soil during the spring. It is a natural method of propagation for blackberry, raspberry, etc. However, gooseberry and creeper rose can also be easily propagated by tip layering.
Mound /Stool Layering or Stooling
The term stooling was first coined by Lynch in 1942 for Mount Layering. It is a method of propagation in which the shoots/plants are cut back to the ground and a mound of soil or rooting medium is applied around the new sprouts/twigs to encourage the roots to develop at their bases. This method is used commercially for the propagation of apple, pear, quince, gooseberry, and other fruit crops. In stooling, the parent plant is cut from 15 to 20 cm above the ground level during the dormant season.
- New shoots/branches will appear within 2 months. Then the ring-shaped bark (girdled) near the base of the new emerge shoot is removed and rooting hormone (IBA) made from lanolin paste is applied to the upper part of the ring. These shoots are left as such for two days for proper absorption of rooting hormone, then covered with moist soil.
- Care should be taken that the mound of soil remains moist at all times. Roots develop in shoots/twigs within 30 to 40 days.
- However, rooted twigs should be separated from the parent plant only after 60 to 70 days and then planted in a nursery or field.
B. Air Layering (Marcottage, Gootee, Pot layering)
Air layering is an ancient method of layering, originally introduced from China and now used commercially for the propagation of many tropical and subtropical trees and shrubs, including litchi, guava, mango, longan, Including Persian limes (Citrus aurantifolia), Ficus, Croton, etc. Cuts are made in spring or summer on the branches of the previous season’s growth. The presence of active leaves on the layered branch accelerates root formation.
The girdled bark about 2 cm wide is removed from the center of the branch or around it. IBA paste is applied over the top of the wound. The wound is covered with moist sphagnum moss so as to cover it completely. A rectangular polythene strip/film is wrapped around the sphagnum moss in such a way that no part is left open, so that moisture can evaporate from the sphagnum moss. After rooting, the branches are separated from the parent plant and planted in the shaded nursery.
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2.Jitendra Singh Basic Horticulture (2011) Kalyani Publications, New Delhi
3.K.V.Peter Basics Horticulture (2009) New India Publishing Agency
4. Jitendra Singh Fundamentals of Horticulture, Kalyani Publications, New Delhi