Time of harvest depends on the intended use of the apples. Apples that will be consumed immediately can be left on the tree longer than those intended for cold storage. Generally, fruit can be harvested from the tree over a couple of weeks. Fruit that drops from the tree is usually over ripe. To determine the approximate time of harvest, check a fruit tree nursery catalog or their web site for a list of harvest dates for various cultivars. These dates will vary depending on location and climatic conditions. A change in background color of the apple peel, flesh firmness, and starch content are other easy methods used to determine harvest time. For some varieties, the peel will change from a greenish color to a yellow color as the fruit ripens. The flesh may also turn from greenish to yellow or white. As apples mature, the flesh often becomes softer and the fruit loses its starchy flavor as it is converted to sugar. Fruit harvested for immediate consumption lacks a starchy flavor. Apples exposed to sunlight always ripen more quickly than those in the shaded, interior part of the tree canopy. For long-term, controlled atmosphere storage of apples, pressure testers are used to determine flesh firmness, refractometers measure percent Brix (sugar content), and a starch-iodine test can be used to determine the optimum date for harvest. For more detailed information on determining apple maturity and harvest dates, see http://agsci.psu.edu/tfpg/part6/AGRS045-06.pdf/view.