It is time to think about planting your spring vegetable garden. You might even want to take the organic approach. Since our soils have lost so many nutrients with the heavy rains, let’s look at the best sources to consider. Where animal manures are available they are probably the best sources of nutrients for the organic gardener.
Manures vary greatly in their nutrient content and degree of decomposition. It is best if the manure is well decomposed or it may actually injure the plant roots. How much should you apply? Before planting, cow or horse manure may be applied at 25 pounds per 100 square feet of garden soil. For best results, supplement each 25 pounds of manure with 2 to 3 pounds of ground rock phosphate or raw bone meal.
If you use poultry or sheep, 12 pounds per 100 square feet supplemented with 1 to 2 pounds of ground rock phosphate or raw bone meal is adequate.
After planting, using cow, horse, or hog manure, side dress with up to 5 pounds per 100 square feet.
When applying a side dress, scatter the manure at the edge of the root zone and work lightly into the soil surface. If a mulch is present, rake it back at the edge of the root zone in order to apply the manure, then recover with the mulch. Remember, manure is not always a complete well balanced fertilizer. It is advantageous to broadcast a complete fertilizer such as organic 8-8-8 plus trace elements or ground rock phosphate and potash in addition to the manures.
If manures are not available, acceptable manure like organic fertilizer may be made through the process of composting. Simply put, compost is made by alternating layers of organic materials, such as leaves and kitchen table refuse, with manure, topsoil, lime, organic fertilizer, water, and air, in such a manner that it decomposes, combines, and yields a good manure substitute. Since compost is an alternative to animal manure, it should be applied as you would manure. Broadcast it over the entire vegetable garden area three weeks or more before planting. Or if you have only a small quantity of compost, it may be mixed into the soil. In all cases, apply it at the rate of about 25 pounds per 100 square feet.
Natural and organic materials that yield plant nutrients upon decomposition are often available for purchase either separately or in combination. These materials may be applied separately or combined, used in the compost pile, or mixed with manure.
Many of the more commonly available materials include both the organic materials derived from plants and animals, plus the natural deposits of rocks and minerals.
Such naturally occurring materials are usually not easily obtained in today’s modern agriculture. However, where available, they are sources of mainly potash, phosphorus, and lime (calcium and magnesium) for organic gardeners.
Rock phosphates are natural deposits of phosphate in combination with calcium. Rock phosphate yields its phosphorous 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 more readily available to plants. If the soil is alkaline, phosphorus may not be available.
Apply ground rock phosphate at the rate of 2-3 pounds per 100 square feet of garden soil, or, when applying manure or compost, mix a the rate of 2-1/2 pounds phosphate per 25 pounds of 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 rock phosphates are so slowly decomposed, side dressings are seldom beneficial. Potash or Potassium is widely distributed in nature, occurring in rocks, soils, tissues of plants and animals. In gardening practice, materials such as wood ashes, banana skins, seaweed, potash salts, and ground rock potash are used alone, in combination 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 combination.
An advantage for using organic materials as fertilizers is that they contain many of the elements also needed by the plants such as zinc and iron.
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 dolomitic lime.
Natural deposits of lime that an organic gardener might use are crushed coral, dolomite, and shell. All these forms must be finely ground to provide maximum benefit to the soil and plants. Lime to sweeten the soil should be applied only when the needs have been established by a reliable soil test. Under most soil conditions, application for 2 to 3 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.
If all this sounds complicated, don’t be discouraged. Not everyone is a soils chemist! There are some great books at local garden shops that will help. Also the University of Hawaii College of Tropical Agriculture and Human Resources Master Gardeners are available to assist. You may call 322-4893 in Kona or in Hilo at 981-5199.