The use of the word "organic" implies a certain standard whether the grower is certified as an organic grower or merely chooses to follow this method of farming. Growing organic apple trees is as complicated for the home gardener as for commercial orchards. In either case, all soil amendments, including fertilizers, must be organic in composition.
What Is Fertilizer
Fertilizer, loosely defined, is anything added to the soil that enhances its nutritive quality and improves plant growth. For organic fertilizers, those additives must come from biological sources rather than man-made solutions or chemical additives. Three types of soil amendments can be used as fertilizer for organic apple trees--animal manures, compost and cover crops.
Soil samples should be taken prior to planting and in subsequent years if growth rate of the apple tree or apple production is not meeting expectations. The soil sample will identify any deficiencies in the soil and recommend basic additives.
Animal manure can be used as fertilizer for organically grown apple trees. Dairy, horse and poultry manure can include the bedding or litter used in the animals' shelter area such as straw. Swine manure can be used without the added bedding materials. These manures will to varying degrees supply a mix of nitrogen, phosphate and potassium, the three most commonly used minerals required by plants. Animal manure cannot be used within 90 days of harvest to prevent fruit from coming in contact with fecal matter.
Compost is a bit trickier as its contents and the procedure for making it organically are regulated. Animal manure and plant materials can be combined in organic compost. Depending on the composting system, specific temperatures must be maintained for a certain numbers of days to achieve the heat levels necessary to break down the organic materials and destroy harmful bacteria. Compost piles must be turned a minimum of five times before they can be used. If they contain animal manure, they cannot be applied less than 90 days prior to harvest.
Cover crops are planted prior to planting the apple trees. They are mowed or clipped and then worked into the soil to enhance the nutrient levels. The type and amount of value added depends upon the soil status, the type of cover crop and the growing conditions. The cover crop can also be left in place after planting to continue to provide nutrients to the apple trees.
Commercial Compost and Fertilizer
The problem small growers have with any of these methods is that specific nutrient values are not available for homemade compost or manure fertilizers as there are too many variables. Commercially prepared organic compost or fertilizer is an acceptable alternative. Producers must be certified and can give a complete nutrient content analysis report to help calculate application rates. This can be quite useful in making sure the right amount of each nutrient is applied, according to Arizona Cooperative Extension. The drawback is they tend to be quite expensive.
Any of the organic fertilizers recommended can be added prior to planting. Later applications should be made only if the apple tree is not growing or producing properly. Applications made after planting can be banded around the tree, about 18 inches out from the trunk. Manures and composts should be tilled into the top 4 inches of soil, also 18 inches out from the trunk.