Montessori-Inspired Fall Activities - links to themed units with LOTS of fall activities for each theme (apples, pumpkins, autumn leaves, squirrel and nut activities, corn, Halloween, and Thanksgiving) as well as Pinterest boards for each theme.
LOTS of Montessori-inspired printables (many free) and activities for a summer- (or anytime) fruit unit study
September and October are great months to focus on apple activities. You'll find special calendar observances here along with LOTS and LOTS of hands-on apple activities (and an Apple Pinterest board, too).
Roundup of Montessori-inspired sewing activities for preschoolers and elementary-age children
Montessori-Inspired Flower Activities (roundup post with lots of activities for home or classroom)
Montessori-Inspired Arbor Day Activities (perfect for Earth Day or a tree unit study at any time)