Know the variety. Yellow Transparent, Gala, and Gravenstein are summer apples, so were ripe this year in mid- to late summer. Most apple varieties ripen in September or October. Know what your apple is supposed to look like when ripe and when it should be ready to harvest. www.orangepippin.com is a good web site for information about apple varieties.
Weather. This summer in Seattle has been especially hot and dry so that fruit is ripening about two weeks earlier than past years
Seed color. As your apples get close to maturity, take one off the tree and cut it open.If the seeds are still light colored, it is too early to harvest, but if the seeds are dark brown to black, your apples should be ready to harvest. Take a bite to confirm that the fruit is sweet enough to harvest.
Skin color. Red apples will get deeper in color as the fruit gets closer to harvest. Green apples will gain a creamy white or yellowish tinge when they are ripe.
Location on the tree. Not all apples ripen at the same time on the same tree. Apples in a sunny spot, especially the south side, ripen before apples in the shade or on inner branches of the tree.
Dropping from the tree. An apple tree will drop diseased or damaged fruit before the crop is ready, but if there is healthy, pest-free fruit on the ground, it's time to harvest.
The best time to pick an apple is when it is almost ready to let go by itself. Lift the apple up gently. If ripe, it will release easily into your hand. If it continues to hang on the tree, it's not ready.
How About European Pears (Bartlett, d’Anjou, Bosc, Comice, etc.)?
European pears do not ripen on the tree. If you wait to harvest these pears until they appear to be ripe, they will be mushy inside. As with apples, a harvest-ready pear should easily come away from the branch when you lift it up. After picking, most European pears will require some amount of chilling, just two days for Bartletts, but 2-6 weeks for winter pears such as d”Anjou and Bosc. After chilling, the pears will ripen in 5-10 days at room temperature.
Asian pears ripen on the tree. The pear is ripe when it is sweet and juicy and has crisp flesh and thin skin. Its aroma should be strong and sweet. Taste it! If it’s sweet and juicy, the pear is ripe.
As for apples and Asian pears, the fruit should easily come off the branch when you lift the fruit up. If you have to pull the pear off the branch, it is not ready to harvest.