Rooting hormones

MANILA, Philippines - Rooting hormones or substances that promote the development of roots are used to increase the percentage of rooting on cuttings. Rooting hormones are called auxins. Auxins applied on cut ends of plant tissues stimulate formation of callus where the roots grow from. Most plants do not need the use of rooting hormones; however, these plants will root faster and more uniformly when treated with auxins.

Some auxins that are commonly used in horticultural industries are: Indolyl Acetic Acid (IAA), Indolyl Butyric Acid (IBA), alpha-Naphthalene Acetic Acid (alpha NAA), and alpha Naphthalene acetamide (alpha-NAAmide).  

Different types of rooting hormones are made with varying concentrations of auxins as active ingredients. The weaker concentrations are used on easy-to-root soft cuttings, while higher concentrations are used on more hard-to-root mature tissues.

Rooting hormones are usually manufactured in liquid or powder forms. The liquid formulations are diluted and cuttings are soaked for a specified time depending on the materials. This technique is useful for homogeneous materials but may cause cross contamination or infestation if materials used are not sanitized. The advantage of using liquid solutions of auxins is that fungicides may be added to the soaking solution. Leftover auxin solution may not be used the next day and must be discarded.

Rooting Powder

Auxin in talc powder carriers are easier to use. There is no soaking time. The cut ends of the cuttings may be lightly dusted with the rooting powder and excess powder shaken off. Care should be taken that the powdered cut end be placed in prepared holes. The medium is then compacted around the cuttings. 

Do not try to push cuttings into solid media if rooting powders are used. This will drive the rooting powder to the media level leaving the cut-end stripped of the needed auxin. Rotting of the cut end usually commences if this happens and the roots if they sprout will be on the upper portion of cuttings (corresponding to the medium level) instead of the bottom.

Since the major cause of failure of cuttings to strike root is infection, fungicides are usually incorporated into the rooting hormone formulations. 

Healthy cuttings derived from healthy mother stocks should root easily. If the mother plant shows any symptoms of chlorosis (yellowing of leaves), it should be corrected first before cuttings are harvested. 

Boron

One of the most common problems in regular extraction of cuttings from motherstocks is that the Boron level may drop to a critical level. Continuous extraction of cuttings from the same mother stocks results in Boron depletion. 

Boron is dubbed the inorganic rooting hormone. Boron is responsible for callus development where the roots will arise. Deficiency in Boron may affect the efficacy of the rooting hormones. Some rooting hormone manufacturing companies incorporate small amounts of Boron to their hormone powder products to be sure.

Extraordinary uses of rooting hormones

Auxins may be applied to healthy plants to induce rooting. Spraying rooting hormones on healthy plants regularly will result in disaster. The auxin will activate the food reserve of the plants (starches) and convert them to free sugars. High levels of free sugars in the cytoplasm will increase the turgor pressure posing a threat of cells bursting. The excess sugar is then condensed by the plant to form a purple pigment called anthocyanin to remedy the hyperglycemic (high sugar) state. 

The auxin will also affect the healthy growing roots. Rooting hormone, auxin while it induces root formation, will ironically stop the roots from growing by heading off the root meristem and make them spit or branch to outright root tip destruction.

Plants (e.g. Orchids) regularly sprayed with hormones will have massive branching roots and anthocyanin pigmented leaves. The leaves grow consecutively smaller and shorter with time giving the plant a cretin (dwarf) look. It is not advisable to give plants a regular spray of rooting hormones. Aside from being counter productive, it permanently destroys the plant form and increases the production cost. 

2,4-D is a very strong Auxin. It is through this mechanism that the farmers use 2,4-D to kill unwanted plants called weeds.

Rooting hormone benefits the farmers through production of uniformly rooted cuttings. A single application is usually what is needed whether it is dipped, sprayed or dusted. Rooting hormones are not recommended for regular use.

Rooting powders in the market

There are several brands of rooting powders in the Horticultural Industry. Most brands use Indole Butyric Acid at different levels. 0.1% IBA for soft cuttings like Begonia, Huperzia, Saintpaulia and Gloxinia; 0.3% IBA for semi-hard cuttings like Hydrangea, Hibiscus and Roses; and 0.8% IBA for woody cuttings like Salix, Mellaleuca, and Hibiscus stems. Most Rooting Powder formulations include a very small amount of Boric acid and a general fungicide (usually for water molds and other damp-off organisms).