Mine knows Solarbeam, Earthquake, Growth, and Petal Dance but I'm really starting to dislike Petal Dance as it locks Venusaur into using the move while the opponent could just switch his/her Pokemon out. Plus, it would be a waste for Venusaur to hold a Persim Berry while it should really be holding a Life Orb.
I was thinking of switching Petal Dance with Synthesis, Toxic, Leech Seed, or Hidden Power (fire), but I don't know which to choose. Help me out!!
If you're using Mega Venusaur I would suggest switching Petal Dance for Synthesis so it can get some recovery back due to it losing Leftovers.
Sythesis|Toxic|Giga Drain|Sludge Bomb
^If you want, but your set is okay.
But you say you're using Life Orb so that means no Mega so I would suggest:
Growth|Giga Drain|Hidden Power [Fire]|Earthquake
This is the Mixed Sun Sweeper set that works really well as Growth will boost both Attack and Special Attack and your Speed will be boosted in the sun.
I would go with Sleep Powder or HP [Fire}.
Sleep Powder helps you set up easier and more, while HP [Fire] gets great coverage with EQ and SB and since I assume you are going to be using this in the Sun, it also gets the boost from the Sun.
Well it depends what your using your Venusaur for and whether your using your Venusaur in a Sun team. If your using it in a Sun team I would keep Solar Beam (Because it's high power, STAB and can be used in one turn). I would also keep Growth (Because it raises your Attack and Special Attack by 2 stages in the Sun). I would replace Petal Dance with Synthesis (as it restores 2/3 of HP in sunlight) and I would also replace Earthquake for Hidden Power Fire (As sunlight boosts Fire Type Moves).
If your not using it in a Sun team I would replace Solar Beam for a much more reliable move such as Energy Ball (because Energy Ball would be 180 power over the course of two turns while Solar Beam would only be 120 and your opponent can simply switch out while your charging). I would give it Leech Seed or Synthesis as recovery. The rest would be up to you, you could give it Earthquake, Sludge Bomb or Sleep Powder or you could even give it Toxic and Protect to stall out.
Hope I helped :)