Environmental Requirements
for Good Plant Growth
Soil
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composed of sand, silt, and clay, organic
matter, living organisms, and pore spaces
classified according to percentage of sand,
silt, and clay they contain.
Ideal Soil Composition
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45% Mineral Matter
25% Water
25% Air
5% Organic Matter
Soil Particles
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vary greatly in size
sand is the largest
silt - medium
clay - smallest
Soil Profile

Consists of 3 basic layers

Topsoil
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Subsoil
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represents depth normally plowed
deep rooting plants send roots down into subsoil
soil bedrock
Water in Soil

Gravitational Water
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Soil is unable to hold against the force of gravity
Of little value to plant as it drains away quickly
Seen more in soils with large pore space
Water in Soil

Capillary Water

Free moving capillary water
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Available capillary water (field capacity)
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Moves in all directions
Remaining water after capillary movement stops
Soil surface is dry and water is a thin film around soil
Most important water for plants (half available)
Unavailable capillary water
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Not available to plants
Held tightly by soil particles and moved as vapor
Types of Soil
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Sandy
Clay
Loamy
Sandy Soil
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Silt and clay make up less than 20% by
weight
Drain well
Little water holding capacity
Clay Soil
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Must contain at least 30% clay
Holds more moisture than is good for plants
Poor drainage
Loamy Soil
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Most desirable soil
Equal parts sand, silt and clay
If more sand, it is sandy loam
If more clay, clay loam
If more silt, silty loam
Soil less Planting Media Mixes

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Many greenhouses and nurseries use soil less
mixes
Advantages of soil less planting media

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Sterile
Lightweight
Easier to handle and ship
Good moisture retention and drainage
Free of weed seeds
Soil less Planting Media Mixes
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Disadvantages
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Light weight - pots tip in strong wind
Minor elements are missing
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Iron
Sulfur
Manganese
Zinc
Calcium
Transplants may not adjust well to new media
Soil less Media Options

Perlite

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Gray-white material of volcanic origin
Improve aeration
Larger particles provide better drainage and
aeration
Vermiculite

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Exploded Mica
Improves aeration
Neutral pH
Plant food and fertilizers
divided into two groups
 Major elements (macro)
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Nitrogen - N
Phosphorus - P
Potassium - K
Plant requirements
large amounts of major elements
 relatively small amounts of minor
elements

Commercial fertilizers

shows % or pounds per cwt.
(100#) of the three major
elements in large numbers on the
container or bag.
Commercial fertilizers
5-10-5
 5% N, 10% P, 5% K
 remaining 80% is filler
 NP&K are always listed in that
order.

Soil tests

determine amount of elements
needed for various plants.
Nitrogen
has most noticeable effect on
plants
 encourages above ground
vegetative growth
 regulates use of other elements

Phosphorous
held tightly by soil particles
 not easily leached
 effects plants in several ways
 encourage cell division

Phosphorous
flowers and seeds don’t form
without it
 hastens maturity, offsetting quick
growth caused by N.
 encourage root growth
 makes K more available

Phosphorous
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increase disease resistance
improves quality of grain, root and
fruit crops
container plants can be damaged by
excess P
increases soluble salt content of
medium
causes dehydration of roots
Potassium
modifies both fast soft growth of
N and early maturity of P
 is essential

Potassium
increase disease resistance
 encourages healthy root systems
 essential for starch formation
 development of chlorophyll
 efficient use of CO2

pH
measure of acidity or alkalinity
 pH scale - runs from 0 - 14
 most plants grow best from 5.67.0

pH
7.0 is neutral
 pH of 7 or above is alkaline or
basic
 pH below 7 is acidic

pH
as numbers decrease, solution
becomes more acidic.
 As numbers increase, solution
becomes more basic or alkaline

pH
if soil is too acidic, lime is added
to raise the pH
 if soil is too alkaline, sulfur is
added

Above ground environment

temperature
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some plants prefer cool weather
some plants prefer warm weather
Temperature
there are temperatures above and
below which plants stop growth
 generally, plant growth rate
increases as temps increase up to
about 90 degrees

Light
must be present before plants can
manufacture food
 plants vary in light requirement
 effects flowering

Photoperiodism

response to different periods of
day and night in terms of growth
and maturity
Photoperiodism

short day plants
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chrysanthemum and Christmas
Cactus
bloom when days are short and
nights are long
Photoperiodism

long day plants

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lettuce and radishes
bloom when days are long and
nights are short
Photoperiodism

day length indifferent

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do not depend on length of light or
darkness
African Violet and tomato
Phototropism

plants appear to grow towards the
sun or light source
Humidity
moisture level of the air
 most plants grow best in 40-80%
RH
 Relative Humidity

Humidity

too high humidity may cause the
spread of fungus diseases
Plant diseases and Insects
reduce production
 lower fruit and vegetable quality

Gases and Air Particles
CO2 is vital to plants for Ps
 Air pollutants can cause damage

Air Pollutants
Sulfur Dioxide - SO2 - from
burning coal
 Carbon Monoxide - CO - exhaust
from cars

Carbon Monoxide
reduces plant growth
 can kill plants
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