I recently planted P. Japonica with the purpose of establishing a windbreak/hedge. My choice of bamboo was based upon a mature hedge I had seen on the property at my local bamboo nursery. I was impressed with the mature hedge and was told it had reached maturity after 5/6 years and is now 8 yrs old. This hedge is most certainly formed in distinct clumps, there are gaps on the ground between plants where no growth has occurred. The owner told me no root pruning took place nor were barriers installed.

From all that I have read and studied it appears that P. Japonica is considered to be a runner , why would it grow in this fashion in our locality ?

On a similar issue I note that a Vivax ( also a runner) that I planted 2 yrs ago has started shooting. I have 4 new culms coming straight from the base ( where the original 2 culms are) making this plant look like a clumper also. I have checked the around this plant but see no sign of action further afield.