Plant Growth Requirements Environmental Requirements for Good Plant Growth
The Plant Environment 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 Air & Liquid = 50% Water = 25% Air = 25% Solid portion = 50% Mineral Matter = 45% Organic Matter = 5% 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.
Soils(Soils will be discussed in detail in a later section) 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 • 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
Functions of Water Provides two essential nutrients to plants. Keeps plants turgid or inflated. Medium for transporting nutrients and food throughout the plant. Necessary for photosynthesis. Maintains stable temperature in the plant.
Effects of Watering Plants Over Watering Shallow root systems Root rot Wilting Nutrient deficiencies Stunted growth Under Watering Decreased Growth Decreased rate of photosynthesis Smaller leaves Shorter internodes Stunted, hardened appearance
How to Determine When Plants Need Watered Learn plant signal (wilting). Watch for drought stress. Discoloration of the plant. 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 Early morning hours Not afternoon Not late afternoon or early evening Frequency When needed Determining factors include: Need Soil Characteristics Environmental conditions
Soil Drainage 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. 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 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 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 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) • Macronutrients • Required in large amounts • nitrogen • phosphorus • potassium • Micronutrients • Required in smaller amounts • calcium • magnesium • sulfur • iron • manganese • boron • copper • zinc
Soil Acidity (pH) 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
Temperature 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 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 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 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 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 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 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.