As a Montessori teacher I have some observations to share. The cooking, outside activities like gardening, and other real, hands-on activities are actually very much part of the Montessori philosophy and should be included as part of the Montessori 3-hour work-cycle whenever possible. Sometimes it's hard to allow free coming-and-going from outside areas, but if you can swing it, having those activities as free choice is ideal!
I would recommend keeping the "imaginative play" elements that are not part of the Montessori philosophy for the afternoon and out of the work period. The Montessori curriculum is very complete and trying to mix Reggio elements that do not fit the philosophy can have unexpected consequences, such as interruption of the children's "flow" experience during work, and confusion between the use of symbolic learning materials for the use of toys. See the discussion thread on Montessori and imaginitive play- I think the starter post was "are there some kids who hate Montessori?"
I tried what you are describing- giving lessons on materials that were not Montessori, but that I thought would benefit the kids, and I found that the kids were missing out on the dense curriculum already inherent in the Montessori materials. Now I only use original Montessori materials, with few exceptions.
BUT, I think it's a great idea to use Reggio in the afternoon! Montessori's original program was actually a full-day program, so you should try looking up what she did. She goes into it in "The Montessori Method," but unfortunately that book was written early in her career and subsequent books are more accurate as to what she found worked best with experience.
