Design:
http://www.schoolplaygrounddesigners.co.uk/Sensory-Gardens.html
http://paxchristi.org.uk/wp/wp-content/uploads/2013/05/Create-a-Peace-Garden.pdf
Choosing plants:
https://www.rhs.org.uk/advice/profile?pid=524 harmful plants
http://www.crocus.co.uk/designing-with-plants/
https://www.rhs.org.uk/plants/search-form
Using the school garden:
http://creativestarlearning.co.uk/developing-school-grounds-outdoor-spaces