Environmental Requirements for Good Plant Growth

Soil  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  45% Mineral Matter  25% Water  25% Air  5% Organic Matter

Soil Particles  vary greatly in size  sand is the largest  silt - medium  clay - smallest

Soil Profile  Consists of 3 basic layers    Topsoil  represents depth normally plowed Subsoil  deep rooting plants send roots down into subsoil soil bedrock

Water in Soil  Gravitational Water    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  Moves in all directions Available capillary water (field capacity)  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  Not available to plants  Held tightly by soil particles and moved as vapor

Types of Soil  Sandy  Clay  Loamy

Sandy Soil  Silt and clay make up less than 20% by weight  Drain well  Little water holding capacity

Clay Soil  Must contain at least 30% clay  Holds more moisture than is good for plants  Poor drainage

Loamy Soil  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  Many greenhouses and nurseries use soil less mixes  Advantages of soil less planting media      Sterile Lightweight Easier to handle and ship Good moisture retention and drainage Free of weed seeds

Soil less Planting Media Mixes  Disadvantages    Light weight - pots tip in strong wind Minor elements are missing   Iron Sulfur    Manganese Zinc Calcium Transplants may not adjust well to new media

Soil less Media Options   Perlite    Gray-white material of volcanic origin Improve aeration Larger particles provide better drainage and aeration Vermiculite    Exploded Mica Improves aeration Neutral pH

Plant food and fertilizers

 divided into two groups  Major elements (macro)  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

 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 5.6 7.0

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  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  chrysanthemum and Christmas Cactus  bloom when days are short and nights are long

Photoperiodism

 long day plants  lettuce and radishes  bloom when days are long and nights are short

Photoperiodism

 day length indifferent  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