It is quite obvious when to pick a strawberry, a raspberry or a currant. The fruit turns colour and becomes pleasant to eat, and since it will not continue in this condition for more than a few days, it must be picked and used.
There is a little more latitude with gooseberries as they can be used unripe for cooking or ripe for dessert. As a rule, picking begins directly the fruits are large enough to be serviceable for cooking but at this stage it is a thinning, rather than a clearing operation. Quite a lot of fruits are left to get larger and to be further thinned until finally some reach full size and ripeness.
Plums, cherries, peaches and nectarines are fruits in which ripeness, readiness for use and picking time all coincide. With apples and pears this is only true of the early varieties, those that are ready to eat in the late summer or early autumn.
A Simple Test
Mid-season and late varieties of apple and pear are picked before they are fully ripe, or perhaps it would be more correct to say that they have two periods of ripeness, one when they are ready to part from the tree, the other when they have acquired their full flavour and correct texture and are ready to be eaten. Most of these later apples are picked in mid-autumn but there is a simple test for readiness for harvesting. A fruit is grasped gently and lifted with the thumb pressing downwards on the stalk. If it parts readily and cleanly from the tree it is ready to pick and it is probable that most of the other fruits on that tree are also ready.