I kept reading the postings here trying to figure out the use of chalk. Chalk is a form of lime which raises the pH or 'sweetens' the soil. The chalk absorbs and retains moisture which one does not want for the typical iris beds. There is no logical reason to use it since adding humus is much more productive as an amendment.
From what I have read, bone meal is an excellent source of plant nutrients but can require as much as a year to break down to where the plant can utilize them.
