Seeds of Strength has the following text:
Target creature gets +1/+1 until end of turn.
Target creature gets +1/+1 until end of turn.
Target creature gets +1/+1 until end of turn.
Sage of hours reads
Heroic — Whenever you cast a spell that targets Sage of Hours, put a +1/+1 counter on it.
So would Seeds of Strength trigger the heroic once or three?