I need a MANDARIN SPEAKING Gardener for a neighbor of mine who speaks little English.

You could start by checking contractors in your area who are members of Hometalk. Perhaps they would know someone. You can find them by using the search box at the top of the page and the dropdown menu for contractors.

try your County's Master Gardeners Program for references. for San Diego County: http://www.MasterGardenersSanDiego.org