Learn to Think Like a PlantLearn to Think Like a PlantThen You Can Talk to ThemThen You Can Talk to Them

David Wm. ReedDavid Wm. ReedDepartment of Horticultural SciencesDepartment of Horticultural Sciences

Texas A&M UniversityTexas A&M University

Plants are Plants are “schizophrenic hermits”“schizophrenic hermits” ! !They “live alone” and “talk to themselves”They “live alone” and “talk to themselves”

Plants “talk” using:Plants “talk” using: HormonesHormones Moving photosynthates, nutrients, etc. from “sources” Moving photosynthates, nutrients, etc. from “sources”

to “sinks”to “sinks” Sensing their environment (day vs. night, day length, Sensing their environment (day vs. night, day length,

length of winter, temperature, rainfall, structures they length of winter, temperature, rainfall, structures they touch, gases in the air, chemicals in the soil, etc.)touch, gases in the air, chemicals in the soil, etc.)

They possess the senses of sight, touch, smell and tasteThey possess the senses of sight, touch, smell and taste To the best of my knowledge, they cannot hear?To the best of my knowledge, they cannot hear?

Learn Plant LanguageLearn Plant Language

We must learn the “language” plants use.We must learn the “language” plants use. Plants don’t use “words” or “nerve impulses”.Plants don’t use “words” or “nerve impulses”. Rather they use hormonal signals, chemical signals, Rather they use hormonal signals, chemical signals,

and environmental signals that “trigger metabolism” and environmental signals that “trigger metabolism” and “turn genes on and off”.and “turn genes on and off”.

If we learn their “communication logic”, then we can If we learn their “communication logic”, then we can “talk” to them and “dictate “ what they do.“talk” to them and “dictate “ what they do.

We’re Going to Talk AboutWe’re Going to Talk About

How plants “see”How plants “see” Their “favorite temperature”Their “favorite temperature” How they know when they are “cut”How they know when they are “cut” How and why they sometimes “kill’ How and why they sometimes “kill’

themselves or parts of themselvesthemselves or parts of themselves A little about their “sexual preference”A little about their “sexual preference”

Let’s “talk” to plants withLet’s “talk” to plants with

LightLight

How do plants “see”?How do plants “see”?

Plants “see” with:Plants “see” with: Chlorophyll Chlorophyll

absorbs light for photosynthesisabsorbs light for photosynthesis CarotenoidsCarotenoids

also absorbs light for photosynthesisalso absorbs light for photosynthesis protects plants from high light and sunburnprotects plants from high light and sunburn

PhytochromePhytochrome determines when the sun rises and setsdetermines when the sun rises and sets assists in determining day length (photoperiod)assists in determining day length (photoperiod)

(actually plants measure night length!)(actually plants measure night length!)

Why are leaves green?Why are leaves green?

Chlorophyll & CarotenoidChlorophyll & CarotenoidAbsorption SpectrumAbsorption Spectrum

(these are the colors of light that power photosynthesis)(these are the colors of light that power photosynthesis)

Plants primarily use red and blue light for photosynthesisPlants primarily use red and blue light for photosynthesisPlants are “partially color blind” to greenPlants are “partially color blind” to green light.

Emission Spectrum ofEmission Spectrum ofArtificial LightsArtificial Lights

Each light has a unique color spectrumEach light has a unique color spectrum

Which light is the best match Which light is the best match for photosynthesis?for photosynthesis?

Let’s “talk” to plants withLet’s “talk” to plants with

TemperatureTemperature

Photosynthesis – RespirationPhotosynthesis – RespirationInteractionInteraction

From: http://ecosys.cfl.scf.rncan.gc.ca/dynamic/photosyn_e.htm

Photosynthesis – RespirationPhotosynthesis – RespirationInteractionInteraction

At optimum temperatures:At optimum temperatures:photosynthesis greatly exceeds respirationphotosynthesis greatly exceeds respiration

““net food storage”net food storage”

As temperature increases:As temperature increases: respiration increases respiration increases (especially night time)(especially night time)

photosynthesis deceases photosynthesis deceases (some enzymes inactivated)(some enzymes inactivated)

At high temperatures:At high temperatures:respiration approaches or exceeds photosynthesisrespiration approaches or exceeds photosynthesis

““net food depletion” net food depletion” and the plant starts starvingand the plant starts starving

Cool Season Crops in the SouthCool Season Crops in the South

Optimum Temperature = 65 to 75 Optimum Temperature = 65 to 75 ooFF Grow great during fall, winter and springGrow great during fall, winter and spring Because their photosynthesis greatly exceeds Because their photosynthesis greatly exceeds

respirationrespiration

In the heat of late spring and early summerIn the heat of late spring and early summerRespiration approaches or exceeds their photosynthesisRespiration approaches or exceeds their photosynthesis

The plants may begin starving to death.The plants may begin starving to death.

Cool Season Plants in the SouthCool Season Plants in the South

Over-seeded ryegrassOver-seeded ryegrass DaffodilDaffodil

Cool season plants die in summer because:Cool season plants die in summer because:1)1) non-adapted species may not store sufficient food to come non-adapted species may not store sufficient food to come

back the next year (ex. tulip)back the next year (ex. tulip)2)2) adapted species will store sufficient food in underground adapted species will store sufficient food in underground

storage organ and only the top dies (ex. ephemerals, daffodil) storage organ and only the top dies (ex. ephemerals, daffodil) 3)3) set seed and “kill” themselves (winter annual, ex. rye) set seed and “kill” themselves (winter annual, ex. rye)

Warm Season Crops in TexasWarm Season Crops in Texas

Optimum Temperature = 80 to 90 Optimum Temperature = 80 to 90 ooFF Grow great during early and late summerGrow great during early and late summer Because their photosynthesis exceeds respirationBecause their photosynthesis exceeds respiration

Texas SummersTexas SummersUpper 90s Upper 90s ooF most of July & AugustF most of July & August

In mid-summer, their photosynthesis & respiration are In mid-summer, their photosynthesis & respiration are more equalmore equal

Therefore, even some warm season plants don’t grow very Therefore, even some warm season plants don’t grow very much in the heat of the summer in Texas much in the heat of the summer in Texas

Many warm season plants only have a flush of spring Many warm season plants only have a flush of spring growth; and may not flush again in late summer/early fallgrowth; and may not flush again in late summer/early fall

Many plants actually go into Many plants actually go into quiescencequiescence in mid-summer in mid-summer in Texasin Texas

High Night TemperaturesHigh Night Temperatures

High night temperatures that are most critical.High night temperatures that are most critical. High night respiration rates “burns-up” High night respiration rates “burns-up”

photosynthates produced during the day.photosynthates produced during the day.Cool-season cropsCool-season crops

starve to deathstarve to deathWarm-season cropsWarm-season crops

go into a summer quiescencego into a summer quiescence

By the way, it is what also ruins our fall color!By the way, it is what also ruins our fall color!

Winter Dormancy or RestWinter Dormancy or Rest

A strategy for temperate perennial plantsA strategy for temperate perennial plants to survive winter. to survive winter.

Trigger?Trigger? short days & decreasing short days & decreasing temperatures.temperatures.

Cause?Cause? > inhibitors (ABA) & < promoters (auxin, GA)> inhibitors (ABA) & < promoters (auxin, GA)

Overcome?Overcome?2-8 weeks constant cold storage @ 32 to 45 2-8 weeks constant cold storage @ 32 to 45 ooFF

200-1,200 cumulative hours outdoors @ 32 to 45 200-1,200 cumulative hours outdoors @ 32 to 45 ooFF

How do you “tell” a plant to come How do you “tell” a plant to come out of winter dormancy or rest?out of winter dormancy or rest?

StratificationStratification

Required for most temperate plant seeds.Required for most temperate plant seeds.

Match Chilling Requirement & Chilling ZoneMatch Chilling Requirement & Chilling Zone

Required for most spring flowering Required for most spring flowering temperature perennial fruit trees, temperature perennial fruit trees,

ornamental trees & shrubsornamental trees & shrubs

Match Chilling Requirement with Match Chilling Requirement with Chilling ZoneChilling Zone

Peach Cultivar

Chilling Hour Requirement

Red Haven Red Globe

Sentinel June Gold

Rio Grande EarliGrande

950 800 750 650 450 250

Let’s “talk” to plants aboutLet’s “talk” to plants aboutDeathDeathand and

DecapitationDecapitation

Plant SuicidePlant Suicide

Plants often kill themselves or part of themselves.Plants often kill themselves or part of themselves.On a routine basis! And, on purpose!On a routine basis! And, on purpose!

Summer & winter annualsSummer & winter annuals Leaf abscission (drop)Leaf abscission (drop)

Flower petalsFlower petals FruitFruit

Usually, the Usually, the signal is the signal is the

“death hormone” “death hormone” ethyleneethylene

Horticulturist Murder PlantsHorticulturist Murder PlantsHorticulturist often kill plants Horticulturist often kill plants

by causing inadvertent by causing inadvertent exposure to theexposure to the

““death hormone” ethylenedeath hormone” ethylene

Cut flowers and fruit Cut flowers and fruit stored enclosedstored enclosed

One rotten apple can One rotten apple can spoil the whole barrel spoil the whole barrel or the whole bouquetor the whole bouquet

Not “emasculating” Not “emasculating” flowersflowers

Improperly adjusted Improperly adjusted heatersheaters

Ethylene is Dr. Jekyll and Mr. HydeEthylene is Dr. Jekyll and Mr. Hyde

Ethylene asEthylene as “Dr. Jekyll” “Dr. Jekyll” stimulates bromeliads to stimulates bromeliads to

flowerflower stimulates the formation stimulates the formation

of pistillate (female) of pistillate (female) flowers on monoecious flowers on monoecious plantsplants

stimulates adventitious stimulates adventitious roots on some plantsroots on some plants

can be used as a defoliant can be used as a defoliant for transplantingfor transplanting

Ethylene is not Ethylene is not always the bad always the bad

guy “Mr. Hyde”guy “Mr. Hyde”

Ethylene can also Ethylene can also be the good guy be the good guy

“Dr. Jekyll”“Dr. Jekyll”

Plant DecapitationPlant Decapitation

What happens when you What happens when you decapitate a stem?decapitate a stem?

Auxin is produced by Auxin is produced by the young leaves the young leaves around the shoot tip.around the shoot tip.

Auxin is responsible Auxin is responsible for apical dominance.for apical dominance.

Decapitation alters the Decapitation alters the flow of auxin down the flow of auxin down the stem.stem.

What happens when you decapitate a stem?What happens when you decapitate a stem?

Adventitious Root FormationAuxin accumulates at the cutwhich stimulates adventitiousroot formation

Lateral Buds Break DormancyApical dominance is removed because the flow of auxin downthe stem is stopped.

How do you “tell” a plant toHow do you “tell” a plant tolook ugly?look ugly?

Dehorning or PollardingDehorning or Pollarding

You can be You can be convicted of convicted of

““crape murdercrape murder” ” for doing this!for doing this!

Let’s “tell” a plant how to growLet’s “tell” a plant how to growinto an attractive, pleasing and into an attractive, pleasing and

functional shape.functional shape.

Pruning to Direct GrowthPruning to Direct Growththinning-out vs. heading-backthinning-out vs. heading-back

Let’s let the plant “tell us”Let’s let the plant “tell us”exactly where to make the exactly where to make the

“surgical cuts”“surgical cuts”

Target PruningTarget Pruning A technique developed by Dr. Alex ShigoA technique developed by Dr. Alex Shigo When a limb is cut, plants will seal-off the When a limb is cut, plants will seal-off the

inside of the xylem (e.g. wood).inside of the xylem (e.g. wood). This is called This is called “compartmentalization”“compartmentalization” Target pruning is a “surgical cut” along the Target pruning is a “surgical cut” along the

line of compartmentalizationline of compartmentalization Anatomically, the “surgical cut” is made Anatomically, the “surgical cut” is made

along a straight line just outside the along a straight line just outside the “bark “bark ridge”ridge” to the top of the to the top of the “branch collar”“branch collar”

Target PruningTarget Pruning

From: www.rittenhouse.ca/hortmag/images/oak.jpg

From: www.clemson.edu/crapemyrtle/pruninginstructions.htm

If you cannot see the branch collar,If you cannot see the branch collar,roughly it is from just outside theroughly it is from just outside thebark ridge at a downward and bark ridge at a downward and slightly outward angle.slightly outward angle.

Target PruningTarget Pruning

Target pruning according to Alex ShigoTarget pruning according to Alex Shigo

Prune Weak CrotchesPrune Weak Crotches

Selectively remove weakSelectively remove weakcrotches, i.e. crotches, i.e.

narrow crotch anglesnarrow crotch angleswith bark inclusionswith bark inclusions

Prune Weak CrotchesPrune Weak Crotches

Selectively remove weakSelectively remove weakcrotches, i.e. narrow crotches, i.e. narrow

crotch anglescrotch angles

This must be done when This must be done when the tree is young; the tree is young;

even ifeven ifit disfigures the tree!!!!it disfigures the tree!!!!

Remember, trees areRemember, trees arepruned for the pruned for the

next generation!next generation!

Let’s “talk” to plants about theirLet’s “talk” to plants about their

Sexual PreferenceSexual Preference

Sexual Preference in PlantsSexual Preference in Plants

Monoecious PlantsMonoecious Plantspossess both staminate (male) and pistillate possess both staminate (male) and pistillate

(female) flowers on the same plant(female) flowers on the same plant

cucurbitscucurbits pecanpecanbegoniabegonia oakoakcorncorn papaya*papaya*

* Actually papaya are sexually confused, they can “go every which way”* Actually papaya are sexually confused, they can “go every which way”

““Why are all my cucumber flowers Why are all my cucumber flowers falling off?”falling off?”

““Well mame, it’s because those “useless” male flowersWell mame, it’s because those “useless” male flowers that emerge early in the spring don’t make babies!!!!!” that emerge early in the spring don’t make babies!!!!!”

No ovary, i.e. “babyNo ovary, i.e. “babycucumber” at basecucumber” at base

of flower.of flower.These are staminate These are staminate

(male) flowers.(male) flowers.

Pistillate Pistillate (female) (female)

cucumber cucumber flowersflowers

““Don’t worry mame, your cucumber plants will startDon’t worry mame, your cucumber plants will startmaking female flowers a bit later in the spring.”making female flowers a bit later in the spring.”

““Let me tell you how you can “talk” yourLet me tell you how you can “talk” yourcucumbers into making more female flowers.”cucumbers into making more female flowers.”

Ovary, i.e. “babyOvary, i.e. “babycucumber”cucumber”

Sexual Preference in PlantsSexual Preference in Plants

The sex of some monoecious plants can be The sex of some monoecious plants can be manipulated with hormonesmanipulated with hormones

EthyleneEthylene

Favors pistillate (female) flower formationFavors pistillate (female) flower formation

Gibberellic AcidGibberellic Acid

Favors staminate (male) flower formationFavors staminate (male) flower formation

FinallyFinally

My wish for today is thatMy wish for today is thatI said at least one thing thatI said at least one thing that

““rocked your world”rocked your world”