Final answer:
Apples typically mature in autumn. This is the season when they reach their full size after developing throughout late spring and summer without adding new cells.
Step-by-step explanation:
Apples most commonly mature in autumn. They begin their development following fertilization, typically in late April. By late spring, all of the cells are present, and over summer, the apples grow to their mature size without the addition of new cells. The conditions in late spring are crucial for the number of cells produced in an apple, which determines its eventual size. Variations in temperature across seasons with spring, summer, and autumn being warm enough support plant growth, leading to the maturation of fruits like apples in autumn.