How much stem to leave when pruning in the fall? Zone 6.?

I've left about 8 inches on my phlox, coreopsis, black eyed susans, should they go all the way to the ground?

How much stem to leave when pruning in the fall? Zone 6.?
i thought id be a smart *** once and mow my wifes stuped plants....the next year they came back with a passion.





i was told NOT to mow the yard after that so it was a win win deal
Reply:I cut mine all the way to ground level, one exception being ground phlox.New growth will begin from the plants crown next spring so on the plants you listed the stem left behind will have no growth,probably does not matter but I like to clean my perennial beds of all dead material.