Read in the veteran organic farmer Chandran Mash's book that turmeric grows well under mango tree and ginger under jack fruit tree. Also a natural farmer Pappachan from Kannur advised me to try planting ginger using just mulch. Put seeds directly in soil, after cutting the pureria cover crop and then put a handful of dried cowdung above seed and then mulch lightly. When the mulch decomposes again mulch do this couple of times. Trying this using turmeric under mango tree.