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Plant Growth Requirements
Environmental Requirements for
Good Plant Growth
The Plant Environment
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In order to grow properly, plants require a
certain environment.
This environment is divided into two parts:
The underground in which roots grow
and live.
The aboveground in which the plant
visibly exits.
The Underground Environment
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Rhizosphere: The 24 inches of soil just
below the earth’s surface.
Soil is made up of sand, silt, clay,
organic matter, and pore spaces which
hold air and water.
Solid portion = 50%
Air & Liquid =
50%
Water = 25%
Mineral Matter = 45%
Air = 25%
Organic Matter = 5%
Soils
(Soils will be discussed in detail in a later section)
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Soils are classified according to the percentage of
sand, silt, and clay they contain.
Soil particles vary greatly in size. A sand particle is
much larger than silt. Clay particles are by far the
smallest.
Clay particles hold water and food elements much
more effectively than larger particles.
A certain amount of clay in all soil is important for
this reason.
Soils also vary greatly in general composition.
Some soils are formed from rock breaking down,
others are formed as certain materials are deposited
by water.
Types of Water in Soil
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Gravitational: Water that is unable to hold against
the force of gravity. It is and becomes part of
ground water. It is of little use to the plant
because it drains away taking soluble plant food
elements with it.
Capillary water: Is held against the force of
gravity. It is held in the small pores of the soil.
There are three types:
Free moving: Moves in all directions
 Available or field capacity: Water left after capillary
movement stops - Roots move toward it.
 Unavailable: Held tightly and can only be moved as
vapor
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Functions of Water
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Provides two essential nutrients to plants.
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Keeps plants turgid or inflated.
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Medium for transporting nutrients and
food throughout the plant.
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Necessary for photosynthesis.
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Maintains stable temperature in the plant.
Effects of Watering Plants
Over Watering
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Shallow root
systems
Root rot
Wilting
Nutrient
deficiencies
Stunted growth
Under Watering
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Decreased Growth
Decreased rate of
photosynthesis
Smaller leaves
Shorter internodes
Stunted, hardened
appearance
How to Determine When Plants
Need Watered
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Learn plant signal
(wilting).
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Watch for drought
stress.
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Discoloration of
the plant.
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Lack of turgidity in
the plant or turf.
Plastic stick
method.
Wetness of the soil.
Methods of Watering
Sprinkler
Drip
Surface
Manual
Time and Frequency of
Watering
Time
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Early morning
hours
Frequency
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Not afternoon
Not late afternoon
or early evening
When needed
Determining
factors include:
 Need
 Soil
Characteristics
 Environmental
Soil Drainage
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Add organic matter
Use of tile drains to remove water from
the soil
Raising plant beds
Place ditches between planting beds
Advantages and disadvantages of
planting media mixes.
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Advantages:
Mix is uniform
Mixes are sterile
Soil less mixes lighter in
weight therefore easier to
handle
Good moisture retention
and drainage are possible
through the proper
combination
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Disadvantages:
Since they are light, the
containers may be blown
over
Mineral content is low Minor plant food
elements may be missing
Plants may hesitate to
extend roots when
transplanted to soils.
Content of Mixes
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Perlite: a gray-white material of volcanic origin. Used to
improve aeration.
Sphagnum moss: the dehydrated remains of acid bog plants,
used in shredded form. Used for covering seed because it has
good moisture retention.
Peat moss: Partially decomposed vegetation that has been
preserved underwater. High moisture holding capacity.
Vermiculite: Very light, expanded material with a neutral pH.
Has a very high moisture-holding capacity.
Limestone: Ground natural limestone.
Tree bark: usually the bark of pine or oak trees broken into
small pieces.
Slow releasing fertilizers: Contain plant food which is
gradually made available to plants.
Plant Food and Fertilizers
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Water is the most important plant food. It
makes up 90% of the weight of plants.
Water is the most limiting factor of plant
growth.
All food elements are dissolved in water
and move into the plant in a soluble form.
Only approx. 1% of the water absorbed is
used by the plant.
99% is lost through the process of
transpiration.
Plant Food Elements
(These will be discussed in a later section)
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Macronutrients
Required in large
amounts
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nitrogen
phosphorus
potassium
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Micronutrients
Required in smaller
amounts
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calcium
magnesium
sulfur
iron
manganese
boron
copper
zinc
Soil Acidity (pH)
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Most plants grow best in pH from 5.6 to 7
Soil at 7 is neither acid or alkaline (basic)
Values lower than 7 indicate acid soils
Above 7 indicate alkaline soils
To lower acidity, use materials such as
sulfur, iron sulfate or aluminum sulfate
To increase acidity, apply lime
The Environment Above the
Ground
Temperature
 Humidity
 Light
 Gases or air particles
 Plant diseases
 Insects
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Temperature
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The temperature of the air has one of the
strongest effects on plant growth
Some plants such as lettuce, cabbage and
kale grow best in cool temperatures
Corn, beans and tomatoes prefer hot
weather
Generally, plant growth increases up to a
temperature of about 90 degrees
Humidity
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The moisture level in the air
Most plants are not affected greatly by
minor changes
When humidity is very high (80-100%),
problems such as the spread of fungal
disease may occur.
Light
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Light must be present before a plant can
manufacture food.
Some plants prefer full sunlight, others
prefer shade
Light also affects plants other ways. Thr
response to different periods of day and
night is called photoperiodism.
Photoperiodism
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Definition: The response of plants to
different periods of light and darkness in
terms of flowering and reproductive cycles.
Short Day: Flower only when days are short
and nights are long. (chrysanthemum and
Christmas Cactus)
Long Day: Flower when days are long and
nights are short. (lettuce and radishes)
Indifferent: Plants that do not depend on
periods of light to flower.
Other Reactions to Light
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Plants grow toward their source of light
because the plant stem produces more
growth hormones on the shady side.
Dehlias develop fibrous root systems
during long days but develop thick storage
organs when days shorten.
Gases and Air Particles
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Carbon dioxide is vital for plant growth
Greenhouse operators find that adding
carbon dioxide to the air increased growth
to plants more than enough to pay for it
Some air pollutants cause damage to the
plant (Sulfur dioxide from coal furnaces
and carbon monoxide from cars)
Plant Diseases and Insects
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Any time a plants is
suffering for disease
or insect damage,
production will
suffer.
Leaf damage
reduces ability to
produce food
Stem damage may
girdle (circle) or clog
up a stem and kill
the entire plant.