Thank, Linda, for your advice about kitchen shears. I'm will try the shears on my harder plastic bottles. I also do use shears for cutting around the cap of the milk jugs, which is probably REALLY smart because cutting a curve with a sharp box-cutter is only for those who like to live dangerously! ;-)
I've now set out another 20 jugs and am in that wonderful position of still having 30 jugs in my garage left, filled with soil just waiting for my next WS frenzy. I'm trying to force myself to wait a few weeks to put out some of the less hardy seeds. Of course, I have more than 30 different types of seeds left!! I will also use individual tall plastic cups.