Methods of Using Plant Growth Regulators on Orchids

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What are plant growth regulators? Orchid enthusiasts may not quite understand, but when you say hormones, they will get it a bit. In the past, like everyone else, I only half understood hormones. I often heard orchid enthusiasts say this is a hormone seedling, that is a bud forced with hormones, and so on. But when asked what hormone was used, and what the benefits and harms of hormones are for orchids, orchid enthusiasts are also at a loss. This creates a sense of mystery about hormones. Recently I have often consulted botanists, so I have some understanding of hormones. Below, let us objectively discuss knowledge about plant growth regulators (hormones), so that orchid enthusiasts can have some understanding of hormone-treated orchids.

Strictly speaking, plant growth regulators do not belong to fertilizers; they should belong to a type of pesticide, but they have a certain relationship with fertilizers. The process of plant growth and development is affected by external environmental conditions such as water, sunlight, potting medium, temperature, and so on, and is controlled by internal genetic factors, while what regulates and controls plant growth activities are certain metabolic substances, namely plant hormones. Plant hormones are endogenous active substances produced by the plant body. They can be transported from the organ responsible for synthesis and this tissue to other organs or tissues. At present, the widely recognized plant hormones mainly fall into five major categories: auxins, gibberellins, cytokinins, abscisic acid, and ethylene. In addition, scientists have also discovered other plant hormones such as brassinosteroids, salicylic acid, jasmonic acid, and so on.

The effects of the five major categories of plant hormones:

I. Physiological effects of auxins

Promote growth, but inhibit growth at high concentrations;

Promote the formation of adventitious roots on cuttings; for example, the main component of rooting agents is naphthaleneacetic acid;

Have a transporting effect on nutrients, and can induce seedless fruit;

Other physiological effects such as causing apical dominance, promoting pineapple flowering, inducing female flower differentiation, and so on.

II. Physiological effects of gibberellins

1. Promote elongation growth of stems,

2. Induce flowering

3. Break dormancy

4. Promote male flower differentiation; GA treatment causes plants with unisexual flowers on the same plant to produce more male flowers

5. Induce parthenocarpy, and so on.

III. Physiological effects of cytokinins

1. Promote cell division, mainly acting on cytoplasmic division

2. Promote bud differentiation

3. Promote cell enlargement

4. Promote lateral bud development and eliminate apical dominance

5. Delay organ senescence; can be used to treat fruit and fresh flowers to keep them fresh and green and prevent fruit drop;

6. Break seed dormancy; can replace light to break the dormancy of light-requiring seeds.

IV. Physiological effects of abscisic acid

1. Promote dormancy;

2. Promote stomatal closure

3. Inhibit growth; this inhibitory effect is reversible;

4. Promote abscission;

5. Increase stress resistance; ABA is known as the stress hormone

V. Physiological effects of ethylene

1. Change growth habits, causing plants to show the characteristic triple response and epinasty;

2. Promote ripening; it is known as the ripening hormone

3. Promote abscission; it is the main hormone controlling leaf abscission;

4. Promote flowering and female flower differentiation;

5. Induce the formation of adventitious roots on cuttings, break dormancy of seeds and buds, and induce secretion of secondary metabolites.

From the day plant hormones were discovered, people wanted to use them in agricultural production. However, the hormones naturally present in plants are extremely low in content, so scientists used other methods such as microbial fermentation to concentrate and extract them, or used chemical methods to synthesize them by imitating the chemical structure of plant hormones. These artificially synthesized or artificially extracted physiologically active substances are called plant growth regulators.

Now I will briefly introduce the types of plant growth regulators on the market:

I. Auxin types:

1. Indoleacetic acid, mainly used to promote rooting. It promotes cell growth and cell differentiation, and so on.

2. 2,4-D, which has auxin-like effects, promoting at low concentration and inhibiting at high concentration.

3. Naphthaleneacetic acid, whose main effects are promoting cell growth and promoting rooting.

4. Atonik, a sodium salt of nitrophenol compounds, has obvious promoting effects on plant growth and development, rooting, flowering, and fruiting. If used too highly, it inhibits the growth of young plant shoots

II. Gibberellin types

Gibberellin is also called 920; it mainly promotes cell growth, breaks dormancy, and promotes early flowering in plants

III. Cytokinin types:

1. 6-Benzylaminopurine, abbreviated as 6-BA, has relatively high cytokinin activity. It is often used in tissue culture. It breaks apical dominance and promotes lateral bud growth.

2. Kinetin, 6-furfurylaminopurine, promotes cell division and tissue differentiation and delays the degradation of protein and chlorophyll.

IV. Plant growth retardant and inhibitor types:

1. B9, also called daminozide, mainly inhibits the transport of auxin in the plant body and the biosynthesis of gibberellins, delays vegetative growth, and makes leaves dark green, small, and thick.

2. Triadimefon, a low-toxicity fungicide, can thicken leaves, reduce leaf area, and delay the growth of parts of the pot surface.

3. Abscisic acid, promotes plant senescence and inhibits the physiological processes regulated by endogenous plant hormones (auxins, gibberellins, cytokinins).

Of course there are many more, and I will not list them all here!

As for the application of plant growth regulators, among orchid enthusiasts they are more or less used. Everything has pros and cons. After use, there are many sprouts and rapid growth. But the resistance of orchids also declines rapidly, making them prone to dying back or producing weak new shoots. The so-called orchid-specific bud and root stimulants sold on the market now more or less contain certain plant growth regulators; it is just that most orchid enthusiasts do not know it. Naturally cultivated orchids have good stress resistance, and their ability to resist pests and diseases is better than those using plant growth regulators. Another point is that the concentration of plant growth regulators is not easy to control, because the dosage of plant growth regulators is especially small, sometimes one part per million, and generally it is not easy to control. If the concentration is high, it is easy to produce the opposite effect. For example, if the gibberellin concentration is high, it easily causes orchid new shoots to grow excessively, and the consequence is lodging. Leaves become thinner and the plants easily die back. When the concentration of 2,4-D is high, it inhibits growth and can even kill the plant, and so on. Therefore, plant growth regulators should be used sparingly or not at all in orchid growing.

(For hormones used to dwarf orchids, there is daminozide (B9). It can be applied together with watering when the potting soil needs water. Spray once every 7 to 10 days with a 0.2% daminozide solution until the front and back of the leaves are moist. This can effectively control plant height, making growth compact and strong and the flowers large and brightly colored.)

Appendix: Table of Uses of Plant Growth Regulators

Plant growth regulators have many different uses. It can be said that from seed germination, rooting, and leaf growth to flowering and fruiting, then seed formation, as well as postharvest fruit and vegetable preservation and seed storage, growth regulators can all be used for regulation. Below are listed various uses and the names of suitable plant growth regulators.

Use - Suitable plant growth regulator name

Extend dormancy of storage organs: maleic hydrazide, sodium naphthaleneacetate, methyl naphthaleneacetate.

Break dormancy and promote germination: gibberellin, kinetin, thiourea, chloroethanol, hydrogen peroxide.

Promote stem and leaf growth: gibberellin, 6-benzylaminopurine, brassinosteroid, triacontanol.

Promote rooting: indolebutyric acid, naphthaleneacetic acid, 2,4-D, daminozide, paclobutrazol, ethephon, 6-benzylaminopurine.

Inhibit growth of stems, leaves, and buds: paclobutrazol, uniconazole, chlormequat, daminozide, pix, triiodobenzoic acid, maleic hydrazide, flutriafol.

Promote flower bud formation: ethephon, daminozide, 6-benzylaminopurine, naphthaleneacetic acid, 2,4-D, chlormequat.

Inhibit flower bud formation: gibberellin, fosamine.

Thin flowers and fruit: naphthaleneacetic acid, carbaryl, ethephon, gibberellin, indoxacarb, 6-benzylaminopurine.

Preserve flowers and fruit: 2,4-D, naphthaleneacetic acid, 4-CPA, gibberellin, chlormequat, daminozide, 6-benzylaminopurine.

Extend flowering period: paclobutrazol, chlormequat, ethephon, daminozide.

Induce female flowers: ethephon, naphthaleneacetic acid, indoleacetic acid, chlormequat.

Induce male flowers: gibberellin

Preserve cut flowers: aminoethoxyvinylglycine, aminooxyacetic acid, silver nitrate, silver thiosulfate.

Form seedless fruit: gibberellin, 2,4-D, 4-CPA, naphthaleneacetic acid, 6-benzylaminopurine.

Promote fruit ripening: ethephon, daminozide.

Delay fruit ripening: 2,4-D, gibberellin, daminozide, kinetin, naphthaleneacetic acid, 6-benzylaminopurine.

Delay senescence: 6-benzylaminopurine, gibberellin, 2,4-D, kinetin.

Increase amino acid content: paclobutrazol, 4-CPA, indoxacarb.

Increase protein content: 4-CPA, simazine, atrazine, naphthaleneacetic acid.

Increase sugar content: glyphosate, fosamine, pix.

Promote fruit coloration: daminozide, indoxacarb, paclobutrazol.

Increase fat content: naphthaleneacetic acid, maleic hydrazide, morphactin.

Improve stress resistance: abscisic acid, paclobutrazol, daminozide, chlormequat.

The issue of hormones is a sensitive topic, and ordinary orchid enthusiasts turn pale at the mention of it. Discussion is welcome; the purpose is to let orchid enthusiasts clearly recognize hormone seedlings.

The Bud- and Flower-Promoting Effects of Growth Hormones on Orchids

In the various growth and development processes of orchid sprouting, growth, and flowering, using plant growth hormones to treat different parts of orchid plants can achieve good results. In particular, for the preservation, continuation, and development of some rare or endangered famous varieties, it has a special role; for accelerating propagation speed, enhancing variety exchange with the outside world, and improving economic benefits, it also has an extraordinary role.

Breaking dormancy and stimulating the sprouting of latent dormant buds on pseudobulbs (reed heads). Separate the old pseudobulbs left year by year from the plant, grouping 2 to 3 connected ones together, then clean off the remaining old leaves, wash them, and let them dry, but throughout the whole process do not damage the latent bud eyes. The steps for hormone treatment are: first drip-coat the latent bud eyes with 0.05% (500 ppm) gibberellin (GA3), and after drying, treat the root crown of the remaining old roots on the pseudobulb and the base of the pseudobulb with 0.1% (1000 ppm) indolebutyric acid (IBA). After treatment, plant them into pots according to conventional cultivation methods depending on the variety. Trials have shown that after treatment, the number of sprouted shoots per orchid plant is significantly higher than in the control.

Promote multiple shoots and rapid growth. For rare and excellent varieties, in order to increase the propagation coefficient, the main current approach is through division. In a large clump of orchid plants, only a few new shoots from the previous year can produce new seedlings, while many-year-old plants do not sprout or produce very few new seedlings. Dividing into single plants for propagation also affects growth vigor, and the new shoots produced become smaller, and may even cause the mother plant to die. Treatment and regulation with plant growth substances can induce new shoots and promote growth. The method is: take the orchid clump out of the pot, wash clean the remaining roots and the soil between the plants, and dry until the fleshy roots become soft rather than brittle; separate plant by plant with a sharp knife, then soak briefly in a 0.08% (800 ppm) carbendazim solution; after it has dried slightly again, use medicinal cotton dipped in 0.01% (100 ppm) 6-benzyladenine to coat the pseudobulbs; then use 0.1% (1000 ppm) indolebutyric acid to soak from the root crown to the root base. Practical use shows that combining the three treatments results in fewer pseudobulb deaths, more shoots, and good growth vigor.

Promote flower bud emergence and flowering. The flower bud differentiation of orchids, besides being constrained by cultivation management (including light duration, the carbon-nitrogen nutrition ratio in the plant life cycle, the degree of division, fertilizer and water conditions, and so on), is also importantly regulated by variety characteristics and exogenous hormones.

Taking Cymbidium goeringii as an example, under generally normal conditions, by the end of July and the beginning of August the orchid plant's growth has gradually become complete and mature. At this time, spraying 0.03% (300 ppm) paclobutrazol (PP333) on the orchid leaves can promote pseudobulb enlargement and provide a material basis for flower bud differentiation in August and September. When applying paclobutrazol as a leaf spray, the pot surface must be covered, and the solution must not be poured directly onto the soil. From practical use, orchid leaves sprayed with paclobutrazol only show thickened leaf texture and deeper leaf color; it has no effect in controlling leaf length. But if the solution is sprayed onto the soil, at flowering time the flower stalks are obviously shorter than normal, losing the ornamental value that orchids should have.

When using plant growth hormones, the following two points must be noted:

The use of plant growth hormones should all be carried out during the orchid plant's growing season and at the physiological development stage of the target part, so as to facilitate material transport and metabolism. The temperature during treatment should not be lower than 15°C.

Plant growth hormones can only regulate the growth and development of plants; they cannot replace management and fertilizer. Only by applying plant growth substances under fine management conditions and reasonable fertilization measures can the effect of doing twice the result with half the effort be achieved.

It is suggested that for those poor pseudobulbs of good flowers that are about to be discarded, rootless plants, and so on, you can give it a try; perhaps there will be a big surprise. As for healthy plants, do not go looking for trouble.

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