That depend on plants drought or osmotic stress tolerance, environmental parameters and etc. But you can calculate osmotic pressure of 50 gl-1 peg 6000 by references below, in our researches indicated that 150gl-1 (about -5 bar) induce enough stress for biochemical responses in wheat and more than 150gl-1 have same effects on Cali in tissue culture environments.
First of all you need to check the osmotic potential of your PEG solution through osmometer for accurate research. However, 50g/L creates nearly -0.5 MPa osmotic potential, which induces mild drought stress in plants. I recommend you to use higher osmotic potential solutions (-10 or 1.2 MPa) of PEG 6000 for inducing drought stress. you can also follow our paper in this regard