There are so many ideas for a unit on apples.  There are opportunities for learning in all areas of the curriculum from reading, language, math, science and social studies. 

Books:

Apple Thief   by Noreen Cotter

Alligator Arrived With Apples, A Potluck Feast by Crescent Dragonwheel

Apple Pie Tree by Zoe Hall

Picking Apples and Pumpkins by Amy Hutchings

Big Red Apple by Tony Johnston

Ten Apples Up On Top by Theo Lesieg

Once Upon a Golden Apple by Jean Little

How Do Apples Grow?  by Betsy Maestro