Apple Fruit Thinning


Fruit thinning is a management practice that reduces the number of fruits per tree in the current season, resulting in increased fruit size of the remaining fruits and increased return bloom and yield in the next season. Although it can be difficult to achieve, fruit thinning is the single most important management strategy in determining the annual profitability of apple orchards.

Intensity of Thinning

Management of crop load is a balancing act between reducing crop load sufficiently to achieve optimum …

How Apple Fruit Size Is Determined and Affected

An apple’s size is determined by the cells that make up the apple. The number of cells, size of each cell, and air space between cells all can play roles in fruit size. An average-sized apple has about 50 million cells. Some apples achieve their larger size by having a larger number of cells, and some achieve their larger size by having larger-sized cells.

Most apple growers strive to produce larger-sized fruit. To achieve this goal, growers should consider the …

Emily Hoover, University of Minnesota

Dr. Emily Hoover is currently the Head of the Department of Horticultural Sciences, overseeing diverse research, extension, and teaching programs.  Additionally she teaches courses in fruit production and teaching pedegogy. Her research has focused primarily on evaluation of winter hardiness and winter protection/adaptation to enhance profitability, efficiency, and sustainability of fruit cropping systems.

Contact Information

305A Alderman Hall
University of Minnesota
1970 Folwell Avenue
St. Paul, MN 55108

email:  hoover@umn.edu

 …

Timing of Apple Tree Bloom

Apple trees begin visible growth in the Spring of the year after having had their chilling requirement met, measured as chilling hours (800-1200 hours),  followed by a specific amount of warm weather, measured as growing degree-hours (approx.. 300 hours).  The first growth to appear in the Spring is the leaves and the trees will bloom approximately 3-4 weeks later. The date on which apple trees bloom in a location can vary annually based upon fluctuating winter and spring temperatures and …

Pollinating Apples

Figure 1. Bumblebee on apple blossom (Alan R. Biggs, West Virginia University)

Apples require cross-pollination for optimal fruit set and size.  Cross-pollination involves the transfer of pollen from one apple cultivar to another by pollinating insects, such as bees which are referred to as pollinators.  The cultivar supplying the pollen is called the pollinizer.  For successful pollination to occur, bloom periods must overlap.  Triploids apple cultivars, such as ‘Mutsu’, ‘Jonagold’, and ‘Shizuka’, cannot supply viable pollen and are unsuitable as …

Apple Harvest and Storage

Apples have two basic requirements for maintaining quality in storage: temperature and humidity. First, however, apples should be harvested at the optimum time to maximize storage length and fruit quality. You should take into account the growing season weather time of bloom, historical harvest date, and fruit flavor, soluble solids (sugar content), flesh firmness, and skin color when deciding when to pick. You can also use the Starch-Index (SI) method for determining apple maturity. (See picture below, and more information …

Standard Apple Rootstocks

standard size tree refers to trees growing on seedling or other non-dwarfing rootstock. If trees on standard rootstocks are not pruned to limit tree size, the trees will reach a height of about 30 feet and have a diameter of about 30 feet. Orchards planted before the 1960s often had only 40 trees per acre and were spaced 40 feet by 40 feet. With good pruning, standard size trees can be planted at about 26 feet x 20 feet …

The whitish over color or “bloom” on the surface of the apple fruit

In the orchard the surface of the fruit with a powdery white coating that can be easily rubbed off. The coating is referred to as bloom and consists of minute scales of wax. The wax is excreted by the epidermal cells of the fruit. The wax coating helps preserve the fruit and reduce evaporation. In an article by Belding et al. (1998) they determined that ursolic acid accounted for 32 to 70% of the hydrocarbons that make up the epicuticular …

Dwarfing Apple Rootstocks

Dwarfing rootstocks typically produce trees that are about 25% to 60% of the size of trees on seedling rootstocks, with a mature height of about 6 feet to 12 feet. Depending on the soil, scion cultivar, and training system, trees on dwarf rootstocks can be spaced at 20 feet x 14 feet (173 trees per acre ) to 14 feet x 4 feet (778 trees per acre). Some of the more progressive apple growers, in regions with less vigorous growing …

What is a Strain of Apple?

A strain is a known cultivar that differs in some way from the natural vegetative characteristics of the original cultivar. The difference may be in fruit color development, fruit maturity or growth habit. For example ‘Daybreak Fuji’ is an early maturing strain of ‘Fuji’. ‘Super Chief Delicious’ is a strain of ‘Red Chief Delicious’.  For some cultivars, there are hundreds of strains that have been found over the years, some of which are no longer commercially available as better strains …