A good rule of thumb is to grab the asparagus by the stalk and slightly bend them until they snap. This method shows where the rough part of the stalk ends and the tender part of the asparagus starts. Once you have done this process with all the asparagus, line them up on a chopping board and trim them at the bottom about 1 thumbnail up from where they snapped. Tip: While some may throw away the asparagus ends. I keep them to make asparagus soup.