Layering and cuttings
How cuttings and layers form roots, types of cuttings and layering, auxins such as IBA, mist and media, crop examples, and hormone dilution sums.
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A short piece of grape cane pushed into moist soil in winter can become a fruiting vine within two years. A guava branch wrapped in moss while still on the tree grows its own roots and becomes a new plant. Both rely on the same ability: plant stems can form adventitious roots, roots that arise from tissues other than the original root system. Cuttings are detached before rooting; layers root while still attached to the parent. Both are cheap ways to produce plants true to type, and both are standard horticulture exam topics.
How adventitious roots form
Root initials arise from cells near the vascular tissue, often in the phloem parenchyma or cambium, after wounding. Some species, such as willow and many figs, have preformed root initials in their stems and root very easily; others must form new ones after cutting.
Factors that favour rooting:
- Auxin, which accumulates at the base of a cutting because it moves downward (polarity). F. W. Went and K. V. Thimann showed in the 1930s that auxin promotes rooting, and synthetic auxins soon became standard.
- Juvenility: shoots from young seedlings or from the base of old plants root far better than adult shoots.
- Carbohydrate reserves and the nitrogen status of the stock plant.
- Etiolation or blanching of the shoot base before cutting.
- Wounding the base, which increases auxin uptake and cell division.
- Environment: high humidity around the leaves, a warm rooting medium (often 20 to 25 °C), good aeration, and adequate but not excessive light.
Rooting hormones
- Indole-3-butyric acid (IBA), the most widely used, stable and effective in many species.
- Naphthaleneacetic acid (NAA), stronger but more likely to injure.
- Indole-3-acetic acid (IAA), the natural auxin, breaks down quickly in light.
Hormones are applied as talc powders, quick dips (a few seconds in a concentrated solution, often 500 to 10,000 ppm) or prolonged soaks in dilute solutions (20 to 200 ppm for hours). Woody, difficult species need higher concentrations than soft, easy ones.
Types of cuttings
| Type | Material | Examples |
|---|---|---|
| Hardwood stem | mature, dormant, leafless wood | grape, fig, pomegranate, rose rootstocks, willow, poplar, mulberry |
| Semi-hardwood | partly matured shoots with leaves | citrus, olive, camellia, many evergreens |
| Softwood | young, soft spring growth | many shrubs, apple rootstocks under mist |
| Herbaceous | non-woody plants | chrysanthemum, carnation, geranium, coleus |
| Leaf and leaf-bud | a leaf blade, or leaf with a bud | African violet, begonia, tea, black pepper |
| Root | pieces of root | breadfruit, raspberry, horseradish |
Crops like sugarcane (setts), cassava (stem pieces), sweet potato (vine cuttings) and tea are propagated commercially from cuttings on a very large scale.
Rooting environment
Leafy cuttings lose water quickly while they have no roots. Mist propagation, developed in the 1940s and 1950s, sprays fine water intermittently over the leaves, keeping them cool and turgid while allowing photosynthesis. Fog systems, polythene tents and non-mist propagators do the same more cheaply. Bottom heat speeds root formation. Media should be clean, well aerated and moisture-retentive: sand, perlite, vermiculite, cocopeat, peat or mixtures.
Layering
Layering is slower than cuttings but succeeds with plants that are hard to root, because the shoot stays supplied with water and nutrients from the parent until its own roots form. Rooting is encouraged by girdling, wounding or bending the stem, which traps sugars and auxin above the wound, by applying IBA, and by excluding light.
- Simple layering: a low shoot is bent down, wounded and covered with soil, leaving the tip exposed.
- Tip layering: the shoot tip is buried; blackberries and black raspberries root this way naturally.
- Compound (serpentine) layering: a long flexible shoot is buried at several points, giving several plants.
- Mound (stool) layering: the parent is cut back to the ground, and soil is heaped around the new shoots, which root at their bases. It is the standard method for clonal apple rootstocks such as M.9.
- Trench layering: whole shoots are laid in a trench and covered as new shoots grow.
- Air layering (marcotting, gootee): rooting a branch high on the plant by girdling and wrapping it in moist moss or cocopeat. Litchi, guava, pomegranate, rubber plant and many ornamentals are propagated this way.
Choosing between cuttings and layers
| Cuttings | Layering | |
|---|---|---|
| Number of plants | many from little stock material | few per parent plant |
| Speed | fast, suited to large nurseries | slow |
| Skill and equipment | needs mist or humidity control for leafy cuttings | simple, little equipment |
| Hard-to-root species | often fail | usually succeed |
Preparing rooting hormone and planning cuttings
Quick-dip solution. A nursery wants 250 mL of 2,000 ppm IBA for semi-hardwood cuttings. Since 1 ppm = 1 mg per litre:
- IBA needed = 2,000 mg/L × 0.25 L = 500 mg (0.5 g), dissolved first in a little ethanol or dilute alkali, then made up to 250 mL with water.
Talc powder. For 3,000 ppm IBA in talc: 3,000 mg per kg = 3 mg per g, so 100 g of talc needs 300 mg of IBA, mixed thoroughly.
Planning. The nursery must supply 2,000 rooted pomegranate plants. Hardwood cuttings root at 70 per cent, and 10 per cent of rooted cuttings fail after transplanting:
- Cuttings needed = 2,000 ÷ (0.70 × 0.90) ≈ 3,175 cuttings.
Key points
- Cuttings root after detachment; layers root while attached to the parent.
- Adventitious roots depend on auxin, juvenility, carbohydrates, wounding and environment.
- IBA is the main rooting hormone; apply as talc, quick dip or soak; 1 ppm = 1 mg per litre.
- Cuttings: hardwood, semi-hardwood, softwood, herbaceous, leaf, leaf-bud and root; mist keeps leafy cuttings alive.
- Layering: simple, tip, compound, mound (apple rootstocks), trench and air layering (litchi, guava).
What the exams ask
- School-leaving and entrance papers: types of cuttings and layering with examples, and the role of rooting hormones.
- Degree and research-fellowship entrances: anatomy and physiology of adventitious rooting, auxins and their concentrations, mist propagation, mound layering of rootstocks, and air layering.
- Professional and nursery examinations: preparing hormone solutions, planning propagation numbers, and propagation calendars.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Why do cuttings from old trees root poorly?
Adult tissue has fewer cells able to form roots and different hormone balances. Cuttings from juvenile growth, such as shoots from the base of the tree or from hedged stock plants, root much better.
Why do my cuttings rot before rooting?
Usually the medium is too wet or poorly aerated, the material was diseased, or the temperature is too high around the leaves while the base stays cold. Use clean, free-draining media and hygienic tools.
When should an air layer be cut from the tree?
When a good mass of roots is visible through the wrap, usually after four to eight weeks in warm weather. Cut below the roots, pot it, and keep it shaded and moist until it establishes.
Sources
- Hartmann, H. T., Kester, D. E., Davies, F. T., Geneve, R. L. and Wilson, S. E. Hartmann and Kester's Plant Propagation: Principles and Practices, 9th edition. Pearson, 2018. Chapters 9, 10 and 14.
- Went, F. W. and Thimann, K. V. Phytohormones. Macmillan, 1937.
- Blythe, E. K., Sibley, J. L., Tilt, K. M. and Ruter, J. M. "Methods of auxin application in cutting propagation: a review of 70 years of scientific discovery and commercial practice." Journal of Environmental Horticulture 25, 166–185 (2007).
- Macdonald, B. Practical Woody Plant Propagation for Nursery Growers. Timber Press, 1986.
- da Costa, C. T. et al. "When stress and development go hand in hand: main hormonal controls of adventitious rooting in cuttings." Frontiers in Plant Science 4, 133 (2013).
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