Gardening - biology.

« 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 thelabel—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 thesemethods 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 candevelop 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 energyneeded 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 topush 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 gardenerremoves extra ones so that the remaining seedlings are evenly spaced and not crowded.

The correct spacing between seedlings depends on how much room themature 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 andthen 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 notlast 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 beprotected 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 asmall 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 aclear 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 formost 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 theclimate 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 plantdiseases 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 thesun 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 fasterthan 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, whichdiscourages 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 holespunched 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 asmulch.

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 includeleaves, 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 undesirablebecause 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 weedsneed 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 damaginginsects can be reduced by growing a variety of plants in the garden.

Different plants attract different insects, including some that attack insect pests.

Another methodfor 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 theplants.

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 gardenpests and other organisms.

Ladybugs, for instance, eat aphids, one of the more notorious garden insect pests, and certain types of bacteria kill insect larva.

Anothermethod 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 insectshave 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 controllingthe 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 sothey 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 andeggplant, 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 anddevelop 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. »