I take it they are in soil?? If so, just wait till right before you water, and pick the plant up, holding it upside down, with your hand supporting the soil...and pull the container off....you will be able to tell easily-- If the containers are too large for this, just look the best you can at the drain holes for roots--
Hope this helps--
It is best if you don't let it get to the point that it is stressing your plants that bad--
Just wait til they are kinda dry, so the soil will be shrunk down, and flip it...carefully just start slipping the pot off...it is easy--