How Plants Grow and Let's Hope They Do!

by O. B. Combs.

O. B. Combs is Professor of Horticulture, University of Wisconsin, Madison.

Fruits and vegetables with specific adaptation to local conditions include:

Okra This crop is closely associated with cotton. It requires hot weather and a long growing season. Though a favorite in the South, many people in other areas have never eaten it.

Sweetpotatoes Another crop that requires warm weather and a long growing season.

Collards This vegetable is found in most southern gardens. Extreme cold the low teens early in winter may kill the plants. Collards have contributed much nutritionally for Southern gardeners. They are very versatile as far as planting and growing are concerned.

Rhubarb requires cooler weather than is found in most of the South. It should not be grown except in mountain areas. Broccoli, cauliflower, brussels sprouts, garden peas, lettuce, onions, beets and carrots should be planted in winter or early spring because hot weather may damage these crops. Some gardeners plant them in early fall and harvest before extreme winter cold.

Many Southern gardeners grow Irish potatoes. These are planted in late winter or early spring and production is good. However, the big question often raised is why Southern-grown potatoes do not store like Maine and Idaho potatoes. Southern potatoes are harvested in extremely hot weather when not fully mature and are easily skinned. Also, this crop requires a cool storage area.

A final thought: The best way for gardeners to cope with the weather is to follow recommendations of the county Extension office.

Fruit and vegetable plants are made up of tiny cells. They grow and reproduce by increasing the number, size and nature of these cells. As growth occurs, several important processes take place. Seeds germinate and become young plants that develop roots, stems, leaves and flowers. When flowers are pollinated, seeds and fruits begin to form.

These processes involve intake of carbon dioxide and oxygen, largely from the air and water, and minerals from the soil. Foods manufactured from these raw materials and stored in fruits, seeds, stems, tubers, leaves and flowers provide nourishment, directly or indirectly, for people and animals.

The most important single process carried on by green plants is called photosynthesis. Energy from the sun is trapped by the green plant, simple sugars are formed, and oxygen is released into the atmosphere. Complex carbohydrates, fats, proteins and vitamins are formed by the incorporation of sugars with mineral elements from the soil.

As plants multiply, enlarge their cells and build new tissues and organs, they break down foods with the aid of oxygen to release energy. This process is known as respiration; carbon dioxide, energy and water are released.

Most vegetables are reproduced sexually from seeds. Most fruits and a few vegetables are reproduced asexually or vegetatively from plants or plant parts. Seeds contain the embryo (live plant) and stored foods. For rapid germination, seeds must be alive and strong enough to break the seed coat and emerge from the soil. They need water, oxygen, and a suitable temperature.

The temperature best suited for rapid germination varies with different plants. Seeds of cool season vegetables such as carrots germinate rapidly at soil temperatures between 50 and 60 F, and seeds of warm season vegetables such as beans between 70 and 80 . Sweet corn seeds, which may require ten days to germinate at 50 , may germinate in two to three days at 80 .

Roots anchor and support plants and absorb water and minerals from the soil. These materials are taken in through root hairs and then moved through the stem to the leaves. Roots are the major storage organs of such vegetables as beets, carrots, and sweet potatoes.

Roots have no chlorophyll, thus they depend upon the leaves for their food supply. Roots must be healthy, unrestricted and undamaged by diseases, insects, or deep cultivation if they are to perform their functions. They must have adequate oxygen.

Too much water from a high water table or over-irrigation on heavy soils may result in insufficient oxygen and serious interference with proper root growth and function.

Root systems differ markedly in their form, spread and depth. The tap roots of carrots grow almost directly downward to considerable depths, and give off many lateral branch roots. The fibrous roots of onions grow an extensive, relatively shallow network of small roots. Some plants, such as apple and other tree fruits, have several large roots for anchorage, with many smaller branch roots.

Stems make up the above-ground framework of plants. They provide support for the plant and contain the food storage and transport tissues.

Water and nutrients from the soil move to the leaves, where sunlight and leaf chlorophyll through the process called photosynthesis manufacture food for plant growth and production of the edible portions. Water, nutrient, and manufactured food movement within the plant occurs in the conductive tissue, known as the xylem and phloem.

Leaves originate from stems and are the principal food-manufacturing organs of green plants. They take in carbon dioxide from the air and allow oxygen and water vapor to escape through small openings mainly on their lower surfaces called stomata. Plants are able to regulate these stomatal openings and thus partially control the loss of water from their leaves.

Flowers are necessary for production of seeds. Beans, peas, and sweet corn are annuals; they produce seeds each year and die when the seeds have matured. Cabbage, beets and carrots are biennials and need some part of two seasons to produce seeds; they die when their seeds have matured. Asparagus and rhubarb are perennials which once established may produce and mature seeds each year, but the plants continue to grow in the same location for several years.

Light is the source of energy for photosynthesis, the food manufacturing process carried on only by green plants. It also influences the movement and position of plant organs and the size, form and structure of plants. The amount of food manufactured depends upon the duration, intensity and quality of light. Whether a plant flowers or not is often determined by the relative length of day and night.

Formation of the green coloring matter (chlorophyll) in plants goes on only in light. Pure white cauliflower and creamy white, blanched celery, endive hearts and asparagus spears are produced by excluding light from these plant parts.

Plants arrange their leaves to insure suitable exposure to light. Excess exposure causes stunting; insufficient light causes tall, weak, light green plants.

Plants such as spinach and Chinese cabbage go to seed if growing when days are longer than 15 hours.

The above-ground parts of plants generally are positively phototropic, they grow toward light; roots of most plants are negatively phototropic, they grow away from light. Tops of plants are negatively geotropic, they grow upward away from the force of gravity; plant roots are positively geotropic, they grow downward toward the force of gravity.

Temperature markedly influences plant growth. All important functions of plants respiration, photosynthesis, absorption, digestion and reproduction are influenced by temperature. Each plant has a temperature range in which it grows best, other factors being equal.

Cool season vegetables such as carrots and spinach grow best at lower temperatures than those preferred by warm season vegetables such as beans and melons. Likewise, cool season vegetables are less susceptible to injury from frost.

Plants started indoors frequently are "hardened" by gradually exposing them to somewhat lower temperatures before they are set outdoors. Certain vegetables such as asparagus, horseradish, Jerusalem artichoke, parsnip, rhubarb and salsify will withstand very low temperatures and may be left in the soil over winter even in areas with severe climate.

Water is the most frequent factor limiting plant growth. It is the principal constituent of plants, and an essential raw material in the manufacture of food. Mineral salts must be dissolved in water before they can move into plants through the root hairs. Oxygen and carbon dioxide enter and leave plants in water solution. Mineral salts and manufactured foods move throughout the plant in water solution.

Water keeps plant cells turgid so that they can carry on their functions. It also helps to keep plant surfaces cool through evaporation from the leaves and stems.

At least 15 chemical elements are needed for the growth of fruit and vegetable plants. These include carbon, hydrogen, oxygen, phosphorus, Potassium, nitrogen, sulphur, calcium, iron, magnesium, boron, manganese, zinc, copper and molybdenum. Some of these such as boron, zinc, manganese, iron, copper and molybdenum are referred to as minor or trace elements, since they are needed by Plants in very small amounts.

The successful gardener must know something about how plants grow. He Must also know the essential needs Of plants and strive diligently to fulfill these needs with care and at the proper time.