A Stem Of A Plant In A Aquarium?

Question

is putting a stem of a plant in your aquarium a bad or good thing and will it grow algae

Answer 1

The stem of an aquatic plant? Or a terrestrial plant?

If a terrestrial plant, it would be bad as the stem would release nitrates and nitrites as it broke down.  

Answer 2

A stem of something like Rotala, Ludwigia, or Bacopa would be fine, and will only grow algae if something else of the tank is out of balance.  If it was a stem of ivy or something terrestrial and was fully submerged, it is guaranteed to rot, which is a bad thing.  Some terrestrial plants (pothos and peace lilies, for example) do fine with just their roots, or lower parts of the plant in the water, but be sure the majority of the plant is ABOVE water.