Seedlings are too young to crop

The plant should be about 10" tall and have about 6-8 sets of nodes. When you crop the plant between the 4th & 5th node or even the 6th and 7th node. You then clone the stock you just cut. Don't rush it. By that time the plant is in vegetation cycle and is strong enough to crop.

Understand now? There is no need to crop the top and trash it.