Add only an apostrophe to plural nouns ending in s: the girls' books, boys' bike, plants' supervisors, families' cars. When a plural noun is possessive but each person "owns" only one item, the item should also be listed in plural form.

Where is apostrophe needed?

The apostrophe has three uses: 1) to form possessive nouns; 2) to show the omission of letters; and 3) to indicate plurals of letters, numbers, and symbols. ​Do not ​use apostrophes to form possessive ​pronouns ​(i.e. ​his​/​her ​computer) or ​noun ​plurals that are not possessives.

Do you need an apostrophe for employees?

The apostrophe makes the plural clearer. ... In your writing, you will almost never need an apostrophe to form a plural. So don't write something like this: "All the employee's have arrived." It should be simply employees. Rule: Mind your p's and q's, but use apostrophes for plurals rarely!