Plant cutting, also known as striking or cloning, is a technique for vegetatively (asexually) propagating plants in which a piece of the stem or root of the source plant is placed in a suitable medium such as moist soil, potting mix, coir or rock wool. The cutting produces new roots, stems, or both, and thus becomes a new plant independent of the parent.
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Typically, striking is a simple process in which a small amount of the parent plant is removed. This removed piece, called the cutting, is then encouraged to grow as an independent plant.
Since most plant cuttings will have no root system of their own, they are likely to die from dehydration if the proper conditions are not met. They require a moist medium, which, however, cannot be too wet lest the cutting rot. A number of media are used in this process, including but not limited to soil, perlite, vermiculite, coir, rock wool, expanded clay pellets, and even water given the right conditions. Some plants form roots much more easily. Soft wood cuttings are planted above ground and hard wood cuttings are totally submerged with soil. With hard wood cuttings, several cuttings are also bound together (to a bushel). Most succulent cuttings can be left on a table and small roots will form, and some other plants can form roots from having their cuttings placed in a cup of water.
In temperate countries, stem cuttings may be taken of soft (green or semi-ripe) wood and hard wood which has specific differences in practice. Certain conditions lead to more favorable outcomes for cuttings; timing, size, location on the plant, and amount of foliage are all important. In temperate countries, stem cuttings of young wood need to be taken in spring from the upper branches, while of hardened wood need to be taken in winter from the lower branches. Common bounds on the length of stem cuttings are between 5–15 centimetres (2.0–5.9 in) for soft wood and between 20–25 centimetres (7.9–9.8 in) for hard wood. Soft wood cuttings do best when about two thirds of the foliage removed, while hard wood stem cuttings need complete foliage removal.
The environment for cuttings is generally kept humid—often attained by placing the cuttings under a plastic sheet or in another confined space where the air can be kept moist—and partial shade to prevent the cutting from drying out. Cuttings in the medium are typically watered with a fine mist to avoid disturbing plants. Following the initial watering, the aim to keep the soil moist but not wet and waterlogged; the medium is allowed to almost dry out before misting again.
A rooting hormone may be administered to "encourage" growth and maturity in plants determined[how?] to be unlikely to grow. Though not essential, several compounds may be used to promote the formation of roots through the signaling activity of plant hormone auxins, and is helpful with especially hard plant species.[clarification needed] Among the commonly used chemicals is indole-3-butyric acid (IBA) used as a powder, liquid solution or gel. This compound is applied either to the cut tip of the cutting or as a foliar spray. Rooting hormone can be manufactured naturally, such as soaking the yellow-tipped shoots of a weeping willow tree in water or to preparing a tea from the bark of a willow tree. Shoots or bark do better when soaked for 24 hours prior to using. Honey, though it does not contain any plant hormones, can also aid in rooting success through its antiseptic quality.
Types of cuttings
Many vegetative parts of a plant can be used. The most common methods are:
- Stem cuttings, in which a piece of stem is part buried in the soil, including at least one leaf node. The cutting is able to produce new roots, usually at the node.
- Root cuttings, in which a section of root is buried just below the soil surface, and produces new shoots
- Scion cuttings, which are dormant ligneous woody twigs.
- Eye cuttings, which are pieces of foliated or defoliated stalks with one or more eyes.
- Leaf cuttings, in which a leaf is placed on moist soil. These have to develop both new stems and new roots. Some leaves will produce one plant at the base of the leaf. In some species, multiple new plants can be produced at many places on one leaf, and these can be induced by cutting the leaf veins.
Although some species, such as willow, blackberry and pelargoniums can be grown simply by placing a cutting into moist ground, the majority of species require more attention. Most species require humid, warm, partially shaded conditions to strike, thus requiring the approach above to be followed. Particularly difficult species may need cool air above and warm soil. In addition, with many more difficult cuttings, one should use the type of cutting that has the most chance of success with that particular plant species.
There are ways of improving the growth of stem cutting propagations. Intensifying light allows cuttings to root and sprout faster, though the heat thus generated could cause the propagation material distress. Azalea cuttings can be mildly heated in water to disinfect it from the fungus pathogen Rhizoctonia, and this could potentially be used for other plants.
Providing the right soil
Depending on the type of soil being used, several additives may need adding to create good soil for cuttings. These additions may include:
- chalk; to increase the pH-value of the soil; a pH of 6-6.5 is to be maintained
- organic substance/humus; to increase nutrient load; keep to a bare minimum though
- sand or gravel; to increase the soil's water permeability
For example with plain potting soil, a third of the container should be filled with sand, to make suitable soil for cuttings.
Providing the right humidity
Although several options can be used here, usually semi-white plastic is used to cover the cuttings. The soil below and from the cuttings themselves is kept moist, and should be aerated once in a while to prevent formation of molds. A plastic bottle can be used as a small greenhouse to provide the right humidity level.
- "How to make your own rooting hormone". Pioneerthinking.com. 2005-11-02. Retrieved 2010-02-21.
- "HO-37: New Plants from Cuttings". purdue.edu.
- "Scion cuttings description". Rooting-hormones.com. 2009-02-01. Retrieved 2010-02-21.
- "Eye cuttings description". Rooting-hormones.com. 2009-02-01. Retrieved 2010-02-21.
- "Certain plant species having more success with certain types of cuttings". Healthrecipes.com. Retrieved 2010-02-21.
- Wallheimer, Brian (January 23, 2012). "Study shines light on ways to cut costs for greenhouse growers". Lopez and Currey. Purdue University. Retrieved July 31, 2012.
- Yao, Stephanie (December 24, 2009). "Hot Water Treatment Eliminates Rhizoctonia from Azalea Cuttings". USDA Agricultural Research Service. Physorg. Retrieved July 31, 2012.
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