Great visual aid and step by step blog entry on this topic can be seen at
That’s a neat guide – some other interesting information on that site, too.
I use the multi-cell tray inserts for seedlings. I make a tool, by taking one of the cells and filling it with Bondo body putty and stick a popsicle stick in it for a handle. When I’m preparing a larger pot, I use the “popsicle” to leave an indentation in the soil exactly the shape of the seedling block. When I remove the potted seedling from the cell, I simply drop it into the indentation. Since it fits perfectly, I don’t have to disturb the roots. I gently smooth the top and the seedling is transplanted without stress. Every time you disturb the roots of a seedling, you stunt the growth for a week or more.