Organic fertilizers high in nitrogen are manure, cotton seed meal, guano, and the by-products of slaughter houses – bone meal, tankage, and dried blood.
The best organic sources of phosphoric acid are bone meal and rock phosphates.
Potash is found in the ash of hardwood trees and seaweed.
The food value of organic fertilizers varies so that they cannot be labeled as precisely as the chemical ones. Organic mixtures are now being packaged, however, with the approximate percentage of each nutrient on the bag.
The oldest of all fertilizers – and still the best – is manure. In addition to its nitrogen and other food content, it is high in humus and contains bacteria which-improve the soil.
With the advent of the motor age, manure has become hard to obtain and rather expensive for the city gardener. If obtained direct from the farm, it has the further disadvantage of often containing seeds which sprout in the flower bed.
Air dried manure in which seeds have been killed is available commercially. Sheep manure is the most commonly sold. Poultry manure is the highest in nitrogen.
Guano is the droppings, feathers, and decayed bodies of bats and marine birds. It is very high in nitrogen, but is not always available.
Bone meal is high in both nitrogen and phosphoric acid and is very slow acting. As long as it is not placed in direct contact with the roots, it can hardly be overused. It is especially recommended for bulbs and for plants like peonies which should not be disturbed for many years.
Tankage and dried blood are so high in nitrogen that they must be used with care and are best used in compost.
Manure and bone meal have a slight alkali effect on the soil. Cotton seed meal has an acid reaction and is valuable for use around acid-loving plants such as azaleas or on soil that is inclined to be alkaline.
Lime and aluminum sulfate are found on the fertilizer shelf at stores, but properly speaking, these are not fertilizers. They do have a definite purpose in the garden, however.
The sole purpose of aluminum sulfate is to acidify the soil. It may be used on soils that are too alkaline, around acid-loving plants, and around hydrangeas to make the flowers blue instead of pink.
Lime has the opposite effect. It counteracts acidity. It has the further effect of improving heavy clay soils by making fine particles of earth stick together. Many gardeners use small amounts of lime on the compost pile to sweeten such acid reactors as sawdust and pine needles. It hastens decomposition, but at the same time releases valuable nitrogen to the air so must be used sparingly.
In addition to fertilizers that may be purchased, there are others that you must make yourself. A compost pile should be in a shady spot in every garden. Compost is what you make it. You may add leaves, grass clippings, clean garbage – potato peels, carrot tops, weeds – sawdust, corncobs, and any other such material available. Sprinkle with manure or tankage and add chemicals if you like. Besides the food value, compost adds invaluable humus to the soil.
Humus is decaying organic matter. The texture of the soil and its water retaining qualities depend upon the humus. A humusy soil has good drainage, is well aerated, and yet retains moisture. Humus is also obtained from decaying mulches.
It is important that you fertilize at the right time. In general, fertilizer should be applied as new plant growth begins. That is usually in spring or fall.
Hot summer suns and cold winter frosts are alike hard on tender plant growth. You should, therefore, fertilize early in the spring after frosts are past so that the growth will harden before summer. If you fertilize in the fall, do it after the burning heat of summer is past but in time for new shoots to harden before winter.
BULBS should be fertilized with a slow acting fertilizer when they are set out. They may also be fertilized – but not with a high nitrogen fertilizer – after they have bloomed and when the foliage is ripening and next season’s flowers forming.
TREES may be fertilized by punching holes at the edge of the leaf line and tamping in fertilizer.
DO NOT FERTILIZE any plant immediately after transplanting. Wait a few weeks until it is established.
Always WATER fertilizers into the soil. Plants can absorb only solutions. Dry fertilizer is not only unusable but is likely to burn the roots.
Several SMALL FEEDINGS a few weeks apart are better than one large feeding.
By considering soil, plants, and results, you can select the fertilizers that will make your garden thrive. Use them wisely at the proper time, and you will be delighted with the results.