Daniel , I use your exact same greenhouse method for individual plants. A few things I found out: You can gradually harden off your interns by letting the bottle stand without the top cap. Next you can place a twig or a narrow piece of something, lifting the bottle only slightly to generate a slight draft from below. All of this in a well lit but shaded position. Direct sunlight will steam and cook your interns. All of these I learnt just like Seil, the hard way. However, its smart not to copy the recognized errors of the rest of us. If this weren't true we would be still trying to invent the wheel or stand shivering in a winter prehistoric cave....
Arturo
