Fertilizers are of two principal kinds, organic and inorganic (or chemical). They are added to the soil because they contain food materials in a condition which the plant can readily absorb. Organic matter itself does not contain all the elements for plant growth, or gives them up so slowly that plants cannot get them fast enough. Fertilizers fill in the nutritinal gaps the same way that garden statuary fills in aesthetic gaps. Chemical fertilizers act faster than the others. They are sold under brand names, or as formulae - for example, 5-10-5, 4-12-4 or 10-6-4.

There are many different types. In all cases, the first number is nitrogen, the second phosphorous and the third potash. The numbers may change but not the order. The numbers represent the percentage of the elements in 100 lbs. of fertilizer. Differences in percentages of the elements have to do with the specific purpose for which the particular fertilizer is designed. The 10-6-4 is generally used for lawns and for feeding trees and shrubs, the other two formulae are general purpose fertilizers for flowers and vegetables.

You will find others much more concentrated or, as they are called, high analysis fertilizers. They are used mostly for liquid feeding, dissolving rapidly in water. The lower analysis fertilizers take a longer time to dissolve and consequently longer to reach the plant. The more concentrated fertilizers reach the plant very fast - among them are 20-20-20, 15-30-15 and similar kinds. They are used during the active growing season. The dosage is 1 to 2 tablespoonfuls in 1 to 2 gallons of water.

Larger amounts either represent waste or may do some plants harm. Feeding is done at ten-day-to-two-week intervals. Used correctly, they result in excellent growth. The lower analysis fertilizers are generally spread on the land in early spring at the time of working the soil. The dosage is three pounds per 100 square feet, worked into the soil. If organic matter is used at the same time, spread the latter first, then apply the fertilizer over it and dig both into the soil.

This is the best and most efficient method for handling both. Organic fertilizers are by-products of
the meat packing industry or manufactured from sewage and from food and oil products. Slow in action, they are also low in the elements discussed. But they do have a beneficial effect on soil and plants. Their slow-acting qualities render them valuable for trees, shrubs and grass, or whenever plants need a long-growing season and a gradual feeding. Organic fertilizers last longer than the chemical group.

They are often mixed so that there is immediate as well as prolonged feeding. Among organic fertilizers sold are bone meal, bone flour or steamed bone meal (the latter is faster than bone meal), dried blood, tankage, fish meal, soybean meal and cottonseed meal. Many are sold under brand names. All have the analysis on the bag or container. Because they are slow they are put on the ground in spring and early summer. Bone meal is often applied in autumn to shrubs, hedges and lilacs.

It has an alkaline reaction, therefore cannot be used on rhododendrons or similar plants. Use four to seven pounds per 100 square feet, the latter quantity if you are using peat moss instead of compost or manure. Dessicated or dried manures form another class. Although they are organic their action lies somewhere between the chemical and the other organics. All are animal manures. Some are mixed with peatmoss and other materials which are beneficial.

Valuable for lawns and gardens alike, they are used in spring and summer during active growth. These make excellent liquid fertilizer or liquid manure. Placed in a bag the manure is suspended in water in any convenient container. The proportion is one pound manure per gallon of water. Allow to stand for a week. Then, dilute the liquid 1 part to 5 parts water before applying to plants. Used weekly during the growing season, liquid manure has an excellent effect on the plants, also for young seedlings just transplanted.