Hello hessian should be ok,I planted a tree last week that was root balled it has hessian and wire netting thr hessian is supposed to rot after 6 months,once the shrub is well established the compost in the pot should be compacted enough to stop any running out,another thing that I read about was using old face coverings (your own)they dont rot very quick,tea bags also do bit they stain flags jezza