Determining the correct spacing for a rootstock/variety combination in a particular orchard is worth a lot of pre-planting thought and effort. Trees that are planted too close together for their vigor will be a struggle to maintain during every year for the life of the planting. Additionally, the amount and quality of fruit production will decline when inadequate light is available throughout the tree. On the other hand, trees that don’t have enough vigor to fill their spacing will result in nonproductive area and less than optimal yields per area. Although this also is a frustration, it is more desirable than spacing too closely. The three primary components to consider in deciding tree spacing within the row are rootstock, variety, and soil fertility. While relative size can be provided by others for various rootstock and variety combinations, the uniqueness of your soil fertility (along with annual cropping) will determine how vigorous the trees in your orchard become. This is often learned by experience, but soil analysis along with advice from other local orchardists, crop consultants, and Cooperative Extension specialists can greatly assist in making reasonable tree spacing decisions. More information is provided at the Apple Tree Spacing Calculator.
Answer provided by Dr. Diane Doud Miller, Ohio State University.