Gardening - biology. I INTRODUCTION Gardening, growing and caring for plants as an enjoyable leisure activity, to produce food, or to create beautiful landscapes with artfully arranged flowers, shrubs, and trees. For some, gardening is a form of exercise, a way to save money on food, or a way to ensure that fruits and vegetables are free from pesticides or other chemicals. For others, gardening is a profession: landscape gardeners design, install, and maintain gardens for a living (see Landscape Architecture). Unlike farmers, who typically produces large quantities of crops using complex equipment, such as tractors and combines, gardeners usually produce plants in smaller quantities, relying on manual tools, such as spades, rakes, and hoes, and small power tools, such as mowers and tillers. Evidence of gardening dates back to 6000 BC. For much of history, functional gardens were more important than pretty ones--people relied on their gardens not only for fruits and vegetables but also for plants used to make medicines and dyes. Elaborate, decorative gardens were found only on the estates of rulers and wealthy people who had slaves or servants to tend the gardens. Gardening for pleasure did not become widespread until the development of the middle class, around AD 1500. With money and time to spare, many began to create gardens for enjoyment, not simply out of necessity, foreshadowing the present-day popularity of gardening as a recreational activity. Today gardening is practiced all over the world. With a little soil, some seeds, and a few basic tools, even inexperienced gardeners can enjoy the rewards of creating a garden and watching it grow. Gardeners with more experience and time can delve more deeply, carrying out research to select appropriate plants, and learning about the particular requirements for each type of plant. The more gardeners apply what they learn, the more their gardens thrive and grow. II SELECTING PLANTS Plants differ in their tolerance for heat, cold, and moisture, so when selecting plants, gardeners must take into account the climate of their region. Gardeners also evaluate the soil type and how much sunlight falls on the proposed site, factors that affect the types of plants that can be grown in a particular area. They consider, too, the plant's life cycle--how long it takes a plant to grow, flower, produce fruits or seeds, and die. Annuals such as petunias bloom and produce seed the same year they are planted, then die when cold temperatures set in. Biennials--hollyhocks, for example--live for two years, producing just leaves the first year. In the second year they produce flowers, and die when the weather turns cold. Perennials, which include shrubs and trees as well as flowers, are plants that live for three or more years. From the plants adapted to a particular climate, soil, and light, gardeners can choose plants for their characteristic appeal. Some popular traits include easy care and attractiveness to butterflies, birds, and other wildlife. In temperate zones, desirable traits may include fall color and a feature such as colorful bark, which makes the plant interesting during the winter, when leaves and flowers are absent. A gardener can experiment with a stunning diversity of interesting garden styles and types. Herb gardens may feature culinary herbs, medicinal herbs, and fragrant herbs. Flower gardens may combine a variety of flowering plants or focus on just one type, such as roses, white-flowered plants, or flowers that bloom only at night. Specialized gardens include rock or alpine gardens, which display plants native to mountains, and water gardens, which host plants adapted to wet conditions. Botanical gardens are designed to display plants for scientific and educational purposes, and in these gardens, the plants are often labeled with their names and their optimal growing conditions. III UNDERSTANDING SOIL Healthy soil is indispensable for a healthy garden. Plants derive water, oxygen for their roots, and essential nutrients from the soil. Soil consists of two components: minerals from weathered rocks and organic matter from decayed organisms and animal wastes. The mineral content of the soil provides plants with nutrients, such as calcium, potassium, and phosphorus. Organic matter improves drainage and helps prevent waterlogged soils, reducing the occurrence of diseases such as root rot. It also binds the mineral nutrients so they remain in the soil and are not washed away. The spaces, or pores, between the tiny particles of minerals and organic matter are occupied by either water or air. Water holds vital dissolved nutrients, while air provides the roots with oxygen. Most plants do best in a soil in which half the pore space is filled with air and half with water. Plants use nutrients obtained from soil to build the cells and tissues needed for growth. Nutrients that plants need in large amounts, called macronutrients, include oxygen, hydrogen, carbon, and an array of minerals. They also need micronutrients, or trace nutrients, which consist of cobalt, chlorine, boron, iron, zinc, molybdenum, nickel, manganese, and copper. Soil texture, the size of the individual soil particles, affects how fast water drains and how well plants absorb nutrients. The largest soil particles are grains of sand. Sand grains fit loosely together with large gaps between them, resembling marbles in a jar. The large pores let water (and the nutrients dissolved in it) drain out too quickly for most plants to absorb it. Clay particles, on the other hand, are very tiny, and they pack closely together, resembling tiny beads in a jar. The pores between clay particles are so small that water drains very slowly. Slow drainage can lead to oxygen deprivation because the water takes the place of air in the pores. Another disadvantage of clay is that it binds water and some nutrients so tightly that most plants cannot absorb them. A third soil particle is silt, which is larger than clay but smaller than sand. Most plants thrive in a soil type known as loam, which contains roughly 50 percent sand, 25 percent clay, and 25 percent silt. A loam soil drains water well, but not too quickly, and as a result, the plant can absorb nutrients more readily. Exceptions include desert plants, such as cacti, which do best in a sandy soil, and cottonwoods, which flourish in silty soils. Plant nutrient absorption is also dependent on a soil's pH, a measure of acidity or alkalinity. The minerals from which a soil formed and the amount of rain that passes through the soil determine its acidity or alkalinity. Pure water has a pH of 7.0, which is neutral--neither alkaline or acidic. Soils with a pH of less than 7.0 are acidic, those with a pH greater than 7.0 are alkaline. Most plants absorb nutrients best in a soil with a pH between 6.5 and 7.5; however, plants such as rhododendrons require an acidic soil, while others, such as lilacs, grow better in an alkaline soil. Acidic soils are more common in the eastern half of the United States, where rainfall is plentiful, while alkaline soils are more common in the drier west. IV FERTILIZING Not all soils have enough nutrients or the right balance of nutrients. In addition, plants remove nutrients from the soil as they grow, so these nutrients must be replaced in order for the soil to remain productive. For these reasons, gardeners enhance soil by adding fertilizer, a material that contains one or more of the nutrients plants need. Fertilizers are divided into two categories: synthetic and organic. Synthetic fertilizers are concentrated salts or minerals, some of which are produced as by-products of petroleum production. Organic fertilizers originate in plants, animals, or minerals and include compost, seaweed, and ground bone. (For advantages and disadvantages of synthetic and organic fertilizers, see Organic Farming.) Fertilizers usually are sold in packages, on which the percentage by weight of the macronutrients nitrogen (N), phosphorus (P), and potassium (K) are listed on the label--always in the order N-P-K. For example, a fertilizer that is labeled 10-5-3 is 10 percent nitrogen, 5 percent phosphorus, and 3 percent potassium. V PLANTING AND TRANSPLANTING Before planting seeds, gardeners prepare, or till, the soil using a variety of methods. Some turn over the soil with a spade, while others loosen it with a garden fork. Then, they rake it smooth before planting. Some gardeners prefer not to turn or loosen the soil because the oxygen that enters the soil when it is tilled by these methods hastens the breakdown of needed organic matter in the soil. Instead, they just dig a small hole for each seed or plant. To keep the soil loose so that roots can develop easily, they keep it covered with grass clippings, compost, or other organic matter. The presence of this organic matter encourages large populations of worms, whose tunneling breaks up the soil. Gardeners plant seeds at different depths, depending on the seed's size and its requirement for light. Seeds contain starch and oil, stored food that provides the energy needed for sprouting, or germination. Small seeds do not hold much food, so they are sown on or close to the soil surface, where they will not require a lot of energy to push through the soil. Larger seeds have enough food reserves to be planted deeper. This gives the root system more time to develop as the seedling, or young plant, grows up through the soil. As a general rule, a seed can be planted three times as deep as the seed is wide. Some seeds, such as lettuce, require light to germinate; these seeds must be sown on or very near the soil surface. Once the seeds are sown, the gardener gently presses down the soil to ensure that the seed touches soil, not air pockets--this soil contact helps keep the seeds moist. Seeds usually are sown close together in case some of them do not germinate successfully. Once the seedlings that emerge are several inches tall, the gardener removes extra ones so that the remaining seedlings are evenly spaced and not crowded. The correct spacing between seedlings depends on how much room the mature plant needs. To prevent the seeds and seedlings from drying out, the gardener keeps the soil damp--not wet--until the seedlings are several inches tall and then gradually tapers off watering. Rather than starting seeds directly in the garden, some gardeners opt to use transplants--young plants purchased from nurseries or grown by the gardener indoors. Transplants are a particularly popular option for gardeners who live in cooler climates with short growing seasons. In a short growing season, good weather does not last long enough for plants grown from seeds to mature. Transplants give the garden a head start. They can be placed in the garden in early spring, but must be protected from the cold. One protective method is to cover each transplant with a transparent milk jug or plastic soda bottle with the bottom cut off, which acts like a small greenhouse to trap heat around the plant. Using the same principle, some gardeners place transplants, still in the pot, outdoors in a large bottomless box with a clear top called a cold frame. The sunlight passes through the top and heats the air in the cold frame. VI WATERING Water is as vital for plants as it is for other organisms. The pressure of water within the plant cells helps the plant's leaves to remain firm. Water also is essential for most of the plant's biochemical reactions. In addition, water stores essential dissolved nutrients. How often plants need water depends on how hot, dry, and windy the climate is, how well the plant tolerates dry conditions, and how deep the roots go into the soil. Plants can be watered at any time of day. However, to avoid plant diseases that thrive in cool, moist conditions and to reduce water lost through evaporation, gardeners water in the early morning, when the air is cool and still, but the sun will soon dry the leaves. The best method for watering plants is to apply the water directly to the soil, rather than over the tops of the plants. The water should be applied at a rate no faster than it can percolate into the soil so that the excess will not run off and be wasted. This technique reduces water lost through evaporation and keeps leaves dry, which discourages diseases. A few tools for watering the soil efficiently include hoses with tiny holes all along their surface, called soaker hoses; plastic tubes with tiny holes punched in them at intervals for drip irrigation; and plastic jugs with small holes punched in the bottom, filled with water, and set beside a plant. Watering large, densely planted areas, such as a lawn, requires a sprinkler. Evaporation of water from the soil can be minimized by covering the soil with a protective layer known as mulch. Mulch acts as a barrier that slows evaporation by reducing the amount of air and heat that reaches the soil surface. Materials that can be used as mulch include leaves, bark chips, grass clippings, and cardboard. VII CONTROLLING GARDEN PESTS Three types of pests can plague gardens: weeds, insects, and diseases. A weed is any plant that grows where the gardener does not want it. Weeds are undesirable because they compete with garden plants for light, water, and nutrients. Common methods for controlling weeds include pulling them up by hand; digging them out; and cutting them off using a hoe or mower. One way to slow the growth of weeds is to cover the soil with a layer of mulch, which blocks out the light and air that weeds need to grow. Weeds also can be controlled by treating them with a weed killer, or herbicide. Like fertilizers, weed killers can be organic or synthetic (see See also Weed Control). Insects damage plants by chewing leaves or other plant parts by sucking the liquid from the plant, or in some cases, by transmitting viruses. The number of damaging insects can be reduced by growing a variety of plants in the garden. Different plants attract different insects, including some that attack insect pests. Another method for preventing insect damage is to cover young plants with a floating row cover, which is a very thin, white, gauzy blanket that keeps many insects away from the plants. Another preventive method is to grow plants bred for resistance to insect pests. Some insects can be kept in check by introducing beneficial bacteria or insects to the garden. This method exploits the natural ecological relationships between garden pests and other organisms. Ladybugs, for instance, eat aphids, one of the more notorious garden insect pests, and certain types of bacteria kill insect larva. Another method to help control insects in vegetable and flower gardens is to rotate crops instead of growing the same type of plant in the same place every year. Many insects have a life cycle that depends on the presence of a certain type of plant. By removing the plant for at least two years, the life cycle can be interrupted, thus controlling the pest. Both organic and synthetic insect-killing materials, called insecticides, also are available to control insect pests (see Pest Control). Diseases caused by fungi, bacteria, or viruses also can damage plants (see Diseases of Plants). In most cases, once a plant has a disease it cannot be saved, though some fungal diseases can be controlled with a fungicide. The best approach to disease prevention is to provide plants with optimum soil, nutrients, light, and water so they can fight off disease, and to grow plants that have been bred for disease resistance or have natural resistance. VIII HARVESTING AND PRUNING Gardeners harvest plants at different stages, depending on how the harvested plants or plant parts are used. Crops grown for their fruit, such as tomatoes and eggplant, are harvested when the fruit is ripe. Some plants are harvested before they flower--lettuce and spinach, for example, are grown for their tender leaves and develop a bitter flavor if allowed to flower. Plants grown for their roots, such as carrots and radishes, are harvested when the root is large enough, but before it gets tough or woody and loses its sweetness. In flower gardens, the sign of maturity is the formation of seeds. Many plants stop flowering once they set seed, so to make plants produce flowers longer, gardeners can remove the faded flowers before they produce seed, a technique called deadheading. Gardeners may attempt to control the shape of woody plants, such as trees and shrubs, by removing, or pruning, branches growing in the wrong direction. They also prune to removed damaged, disease, or dead branches. Some shrubs, such as lilacs, bear the most flowers in young wood, so gardeners remove the oldest branches. Gardeners prune plants at different times of the year, depending on how they hope to affect the plant's growth. IX PREPARING THE GARDEN FOR WINTER In regions where winter is characterized by freezing temperatures, the gardening season ends in autumn. In these areas, autumn tasks for vegetable gardeners include removing old plants from the garden. This helps eliminate insects and disease organisms that may survive the winter in dead leaves or flowers. To prepare the soil for the following spring, gardeners may work manure or other fertilizer into the soil, or they may add compost, partially decayed organic material that improves water drainage in the soil. Flower gardeners also may remove annual flowers from the garden to control insects and disease. To preserve perennials, gardeners cover the ground with a deep layer of mulch to prevent the soil from thawing too early. Soils that repeatedly freeze and thaw during the winter can push the roots of perennial plants out of the soil, a process called heaving. Some gardeners try to extend the growing season by protecting vegetables and annual flowers through the first mild frosts of autumn. One popular method is to cover the plants with plastic or bed sheets when frost threatens, which traps heat that the soil gives off at night and keeps frost from settling on the plants. Another technique is to surround the plants with milk jugs or other containers filled with water. As the water freezes it gives off heat, and the slight increase in temperature is enough to protect the plants. In late winter or early spring, before new growth begins, gardeners may cut back the brown leaves of ornamental grasses and the dead branches of perennials so the plants will look tidy as the growth begins again. X LEARNING ABOUT GARDENING In the United States, gardeners have access to a wealth of gardening information. Each state, for example, has a specialized college called a land-grant college, one of whose missions is to help educate the public about gardening. Land-grant colleges have county cooperative extension services, with agriculture or horticulture agents available to answer questions and provide expert gardening information about regional growing conditions. In some county cooperative extension offices, trained volunteers called master gardeners often host information sessions at public places such as libraries or gardening stores. Botanical gardens also hold classes and tours. Gardening clubs found in many neighborhoods are valuable sources of information, particularly about local growing conditions. And an array of gardening books, magazines, and Internet sites caters to almost every gardening interest. Contributed By: Erin Hynes Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.
