Keys to the best fertilizer

  • With access to soil building manures, vegetables like this Swiss chard grow extra large and healthy. (Photo courtesy / Voltaire Moise)

We are exploring New Zealand’s North Island finding lots of aloha and even more sheep. This is a real advantage because farmers and home gardeners have access to abundant manure to enrich their soil.

Where animal manures are available they are probably the best source of fertilizer and organic matter for the organic gardener whether they be in New Zealand or Hawaii.


Manures vary greatly in their content of fertilizing nutrients. The composition varies according to type, age, and condition of animal; the kind of feed used; the age and degree of rotting of the manure; the moisture content of the manure; and the kind and amount of litter or bedding mixed in the manure.

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 of row.

When applying a side dressing, scatter a band of manure down each side of the row. Place each band at the edge of the root zone and work lightly into the soil surface. If mulch is available, rake it back at the edge of the root zone in order to apply the band of manure, then cover with the mulch. Remember, manure is not always a complete, well-balanced fertilizer. It is advantageous to broadcast a complete organic fertilizer or ground rock phosphate and potash in addition to the manures.

If manures are not available, acceptable organic fertilizer may be obtained 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 substitute for manure. Since compost is organic and manure like, it may be used as you would manure. Broadcast it over the entire garden three weeks or more before planting. Or if you have only a small quantity of compost, it may be mixed into the soil along each planting furrow or at each hill site. 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 represent sources of mainly potash, phosphorus, and dolomitic lime (calcium and magnesium) for organic gardeners.

Rock phosphates are natural deposits of phosphate in combination with calcium. The material as dug from the earth is very hard and 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 available to garden plants. Apply ground rock phosphate at the rate of 2-3 pounds per 100 square feet of garden soil. When applying manure or compost, mix at 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 materials are so slowly decomposed, side dressings are seldom beneficial. One caution when it comes to phosphorus is that many plants in the Protea family like macadamia are sensitive to excessive phosphorus so don’t over do it.

Potash or potassium is widely distributed in nature, occurring in rocks, soils, tissues of plants or animals, and water of seas and lakes. In gardening practice, materials such as wood ashes, banana skins, seaweed, potash salts and ground rock potash are used alone. They may also be used in combination with other materials yielding 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 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. Check with the University of Hawaii Master Gardeners in Kona at 322-4892 or at the UH Komohana Ag Complex in Hilo for soil testing information. 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 availability.

If soil science gets a bit too much, remember there are also several good books available like Sunset’s Western Garden Book to assist you in soil chemistry. You may also sign up for the next class series of training to become a Master Gardener.