Spawning rows of moving blocks, tetris-ish game?

So I've got 10 syncro spawners just off-screen in a row.  They spawn 10 random blocks from the same pool simultaneously.  The blocks are already coded to start moving across the screen until they are destroyed, so all that works fine thus far.  I've been trying to play around with timing to get a second row to spawn immediately behind the first, then a third and so on (so that the blocks are all touching - I need their colliders to be able to read each other), but I've been unsuccessful.  What would be the best way to handle this?  Am I correct in thinking that I would need to have each spawner set up to repeat the wave?  Or is there simply no way to have them appear this precisely without code.  I've worked out a few things with code, but I'm far from experienced.  Anyway, I hope I've explained the question well enough.  Any advice would be greatly appreciated.