stem plants you usually trim from the bottom and replant unless i should be corrected. they'll grow roots again eventually. if you notice white roots coming out part way off the stem then that's a good place to trim right below and then replant. my anacharis and wisteria does it. if you "top" them then typically you'll get two shoots from where you remove it. good way to propagate a plant if you want more stems to plant. or if you want something to bush out and stay shorter. i'm not good enough with plants to really identify what all you have but some don't like a lot of pruning from what i'm told. like fisheggs says it really depends