Growth Stimulants, Retardants, and Rooting Hormones

Growth Stimulants, Retardants, and Rooting HormonesGrowth Stimulants, Retardants, and Rooting Hormones

Growth regulatorsGrowth regulators

Hormones

Organic chemicals that act and interact to affect growth rate

Auxins – accelerate growth by stimulating cell enlargement

Hormones

Organic chemicals that act and interact to affect growth rate

Auxins – accelerate growth by stimulating cell enlargement

GibberellinsGibberellins

Stimulate growth in stem and leaf by cell elongation

Stimulates premature flowering, growth of young fruits and breaking of dormancy

Stimulate growth in stem and leaf by cell elongation

Stimulates premature flowering, growth of young fruits and breaking of dormancy

CytokininsCytokinins

Stimulate cell division

Work along with auxins

Will not work without auxins present

Stimulate cell division

Work along with auxins

Will not work without auxins present

InhibitorsInhibitors

Abscisic Acid and Ethylene Gas

inhibits seed germination

Inhibits stem elongation

Hasten ripening of fruit – ethylene gas

Abscisic Acid and Ethylene Gas

inhibits seed germination

Inhibits stem elongation

Hasten ripening of fruit – ethylene gas

Auxins and Gibberellins promote cell enlargement

Cytokinins stimulate cell division

Auxins and Gibberellins promote cell enlargement

Cytokinins stimulate cell division

Growth HormonesGrowth Hormones

Organic chemicals produced by actively growing plant tissue

Shoot tips and young leaves

Move throughout the plant and can be found in most tissues

Organic chemicals produced by actively growing plant tissue

Shoot tips and young leaves

Move throughout the plant and can be found in most tissues

These chemicals react with one another in a very complex system in the plant

In some cases a concentration of one hormone stimulates growth and a different concentration restricts growth

These chemicals react with one another in a very complex system in the plant

In some cases a concentration of one hormone stimulates growth and a different concentration restricts growth

Apical DominanceApical Dominance

Dominance of the terminal bud

Apical dominance exists there

Terminal bud secretes chemicals that inhibit or prevent the growth of axillary buds on the same shoot

Dominance of the terminal bud

Apical dominance exists there

Terminal bud secretes chemicals that inhibit or prevent the growth of axillary buds on the same shoot

Apical DominanceApical Dominance

Axillary buds are found in the axil – angle between a leaf and the stem.

Causes the plant to grow tall and not branch

Once the plant reaches flowering age and the terminal bud becomes a flower, the chemicals are no longer secreted

Axillary buds are found in the axil – angle between a leaf and the stem.

Causes the plant to grow tall and not branch

Once the plant reaches flowering age and the terminal bud becomes a flower, the chemicals are no longer secreted

Apical DominanceApical Dominance

The plant then starts to send out side branches

This allows the plant to grow above competing plants

Once height and access to sunlight are secured, the plant spreads out over its competitors

The plant then starts to send out side branches

This allows the plant to grow above competing plants

Once height and access to sunlight are secured, the plant spreads out over its competitors

Apical DominanceApical Dominance

Pinching off terminal buds removes the hormone and causes branching to happen faster

Common practice in greenhouses and nurseries to produce bushier plants with many flower buds

Pinching off terminal buds removes the hormone and causes branching to happen faster

Common practice in greenhouses and nurseries to produce bushier plants with many flower buds

StimulantsStimulants

Allow plants to grow taller

Most common is Gibberellic Acid (GA)

Causes stems of plants to stretch out

Nodes are farther apart

Allow plants to grow taller

Most common is Gibberellic Acid (GA)

Causes stems of plants to stretch out

Nodes are farther apart

Growth StimulantsGrowth Stimulants

Natural growth stimulants have been found in alfalfa

It causes stimulation of growth

It is the alcohol called Triacontanol

Stimulation is brought about by mulching plants with alfalfa hay

Natural growth stimulants have been found in alfalfa

It causes stimulation of growth

It is the alcohol called Triacontanol

Stimulation is brought about by mulching plants with alfalfa hay

Or watering plants with a “tea” made from soaking alfalfa feed pellets in water

Amount needed is very small

Also sold commercially

Or watering plants with a “tea” made from soaking alfalfa feed pellets in water

Amount needed is very small

Also sold commercially

Chemical RetardantsChemical Retardants

Chemicals are used to retard growth of plants causing them to be shorter and more compact

Plants are more attractive and the plants themselves are stronger

Used commercially

B-Nine is commonly used on Azaleas

Chemicals are used to retard growth of plants causing them to be shorter and more compact

Plants are more attractive and the plants themselves are stronger

Used commercially

B-Nine is commonly used on Azaleas

Newest uses of Plant Growth Retardants (PGR) is the application to lawns

After first mowing in the spring “Limit” is applied and absorbed by the roots

Restricts growth for 6-8 weeks

Newest uses of Plant Growth Retardants (PGR) is the application to lawns

After first mowing in the spring “Limit” is applied and absorbed by the roots

Restricts growth for 6-8 weeks

“Embark” is absorbed by the leaves and also restricts growth

PGR’s absorbed by the leaves move to the growing point where it interrupts cell division, stem elongation and seed head formation

Roots continue to grow

Applied after first or second mowing

“Embark” is absorbed by the leaves and also restricts growth

PGR’s absorbed by the leaves move to the growing point where it interrupts cell division, stem elongation and seed head formation

Roots continue to grow

Applied after first or second mowing

SumagicSumagic

New growth retardant

Reduces height of plants by inhibiting production of GA

Chemical is taken up by leaves and moves through the plant to the terminal bud

New growth retardant

Reduces height of plants by inhibiting production of GA

Chemical is taken up by leaves and moves through the plant to the terminal bud

Used to control growth of shrubbery and hedges

PGR Atrimmic applied after pruning can last an entire season

Reduces or eliminates the need to prune

Used to control growth of shrubbery and hedges

PGR Atrimmic applied after pruning can last an entire season

Reduces or eliminates the need to prune

AtrimmicAtrimmic

A systemic

Penetrates the plant, enters the plant sap, and moves through the plant

Blocks plant hormones that stimulate growth

Applied as a foliar spray

A systemic

Penetrates the plant, enters the plant sap, and moves through the plant

Blocks plant hormones that stimulate growth

Applied as a foliar spray

Rooting HormonesRooting Hormones

Important when propagating plants by cutting

Helps cuttings to develop more roots faster than without a rooting hormone

Indoleacetic Acid (IAA) naturally occurring, causes roots to form on plant stems

Important when propagating plants by cutting

Helps cuttings to develop more roots faster than without a rooting hormone

Indoleacetic Acid (IAA) naturally occurring, causes roots to form on plant stems

IBA – Indolebutyric AcidIBA – Indolebutyric Acid

Most widely used rooting hormone

Most effective rooting hormone

Most widely used rooting hormone

Most effective rooting hormone

Rooting HormonesRooting Hormones

Either mixed with talc and used as a powder or dissolved in water and used as a wet dip

Liquid can be slightly more effective

All rooting hormones should contain a fungicide

Either mixed with talc and used as a powder or dissolved in water and used as a wet dip

Liquid can be slightly more effective

All rooting hormones should contain a fungicide

FungicideFungicide

Helps prevent cuttings from rotting Helps prevent cuttings from rotting

Dwarfing RootstockDwarfing Rootstock

Used in fruit trees

Shorter trees enable you to pick fruit without using a ladder

First research done to prevent apple trees from growing very tall

Trees growing from certain types of roots didn’t grow as tall

Used in fruit trees

Shorter trees enable you to pick fruit without using a ladder

First research done to prevent apple trees from growing very tall

Trees growing from certain types of roots didn’t grow as tall

These trees also bore fruit at an earlier age

Complete series of rootstock known as malling rootstock developed in England

Controls size and rate of growth or apple trees

These trees also bore fruit at an earlier age

Complete series of rootstock known as malling rootstock developed in England

Controls size and rate of growth or apple trees

Stock has also been developed for peach and pear trees as well

Dwarf trees can be purchased commercially

Stock has also been developed for peach and pear trees as well

Dwarf trees can be purchased commercially

Chemical Blossom SetChemical Blossom Set

Used on tomato blossoms early in the season

Causes earlier development of fruit

Causes seedless tomatoes to set on first blossoms and results in tomatoes ready to eat as much as 10 days earlier than normal

Used on tomato blossoms early in the season

Causes earlier development of fruit

Causes seedless tomatoes to set on first blossoms and results in tomatoes ready to eat as much as 10 days earlier than normal

Plant BiostimulantsPlant Biostimulants

Natural products

Organic

Work to stimulate soil microbial activity and improve soil cation exchange capacity, stimulate plant growth and promote disease resistance

Natural products

Organic

Work to stimulate soil microbial activity and improve soil cation exchange capacity, stimulate plant growth and promote disease resistance

Humic AcidHumic Acid

Product of rotting organic matte is an example of a soil microbial stimulant

Product of rotting organic matte is an example of a soil microbial stimulant

Root growth biostimulantsRoot growth biostimulants

Improve water and nutrient uptake

Increase number of fibrous roots

High levels found in kelp plants

Improve water and nutrient uptake

Increase number of fibrous roots

High levels found in kelp plants

BiostimulantsBiostimulants

Greatly reduce the need for fertilizers, especially N

Saves money, reduces pollution

Greatly reduce the need for fertilizers, especially N

Saves money, reduces pollution

MethanolMethanol

A form of alcohol

Speeds plant growth

Research in California showed an increase in plant yield of 36-100%

Works by blocking photrespiration

Plants use water for growth rather than transpiring it into the air

A form of alcohol

Speeds plant growth

Research in California showed an increase in plant yield of 36-100%

Works by blocking photrespiration

Plants use water for growth rather than transpiring it into the air

MethanolMethanol

Works best on plants frown in full summer sun

Water use reduced by as much as 50% in some plants

Works best on plants frown in full summer sun

Water use reduced by as much as 50% in some plants

AllelopathyAllelopathy

Production of a chemical compound in one plant that slows or stops the growth of another plant

Natural herbicide

Black Walnut, Millet

Production of a chemical compound in one plant that slows or stops the growth of another plant

Natural herbicide

Black Walnut, Millet