Natural and organic fertilizers in your garden.

Natural and organic materials which yield plant nutrients upon decomposition are often available for purchase either separately or in combination. These materials may be applied to the garden separately or combined, used in the compost pile, or mixed with manure.

Natural deposites (rocks, sands, shells, etc.) Such naturally occurring materials are usually not easily obtained in today's modern agriculture; however, where available they represent sources of mainly potash, phosphorus, and lime (calcium and magnesium) for organic gardeners.

Phosphorus -- Rock phosphates are natural deposits of phosphate in combination with calcium. The material as dug from the earth is very hard and yields its phosphorus very slowly. When finely ground and with impurities removed, the powdery material is only slightly soluble in water, but may be beneficial to plants in subsequent seasons following application. The reaction of phosphate rock with acids from decaying organic matter in the garden or compost tend to make the phosphorus available to garden plants. Collodial phosphate is also available and widely used.

Apply both phosphates at the rate of 2-5 pounds per 100 square feet of garden soil.

Or, when applying manure or compost, mix at the rate of 2½ pounds phosphate per 25 pounds manure or compost.

Broadcast the material over the soil surface and work into the topsoil at least three weeks before planting. Manure or other organic fertilizer should be added at this time.

Since the materials are so slowly decomposed, sidedressings are seldom beneficial.

Potash -- Potassium is widely distributed in nature, occurring in rocks, soils, tissues of plants and animals, and water of seas and lakes.

In gardening practice, materials such as wood ashes, tobacco stems, wool suint, seaweed, potash salts, greensand, and ground rock potash are used alone, in combinations with other materials yielding other nutrients, mixed with manure, or in compost piles.

Since the potash bearing materials vary so much in composition and rate of decomposition, specific application rates must be determined for each material and its combinations.

In general, ground rock potash at 5 pounds per 100 square feet may be broadcast over the soil surface three weeks prior to planting and spaded in. Langbeinite (Sul-Po-Mag) is used at 1 lb/100 sq ft.

Micro-nutrients -- An advantage for using organic materials as fertilizers is that they contain many of the elements also needed by the plants in addition to N, P, and K (for example, manganese in manure).

Besides the general amounts of micronutrients found in most organic materials, certain ones are concentrated into such naturally occurring materials as gypsum (calcium and sulfur), marl (calcium), dolomite (Calcium and magnesium), limestone (calcium), basic slag (iron, calcium, manganese and magnesium), and finely ground borosilicates.

Lime -- Reducing the acidity of the soil is the primary purpose for using lime in the garden. However, liming materials also provide nutrients for plant use. Calcium and magnesium are the two elements most commonly provided by lime. Gypsum is used where more calcium is needed without raising the pH.

Natural deposits of lime which are an organic gardener might use are limestone, dolomite, shell, and marl. All these forms must be finely ground to provide maximum benefit to the soil and plants. Dolomite is preferred due to its ocntent of both calcium and magnesium.

Lime to sweeten the soil should be applied only when the needs have been established by a reliable soil test. Under most Florida soil conditions, applications of 2 to 5 pounds of finely ground dolomitic limestone per 100 square feet usually will be sufficient except on very acid soils.

Apply lime well in advance of the planting date, preferably 2 to 3 months before the garden is planted. Mix well with the soil and keep moist for best reaction. Application closer to planting time is permissible, but its benefits are delayed.