Tropius is actually a pretty cool Pokemon, and it has a nice offensive typing, with dual STAB's over a large amount of Pokemon. However, the two things that sealed it off were it's extremely shallow movepool, and the terrible defensive typing it received. Also, when I say extremely shallow movepool, it really has, A REALLY. SHALLOW. MOVEPOOL. It does however, get two very nice abilities, Solar Power and Chlorophyll. He has a decent bulk, and a nice HP, with workable (but still low) offensive stats. Despite his few niches, he is not going to see much use within tiers, and even the NU tier.
Chlorophyll: Doubles speed within the sunny weather.
Solar Power: Takes away 1/10 of your HP to increase the move's power by 1.5.
Harvest: Recycles a berry infinite times with a 50% chance.
-Hidden Power [Ground]
EV's: 252 special attack, 252 speed, 4 HP
Item: Choice Specs
This is actually the best set, and the only set, you should run, and I'll tell you exactly why. The modest nature is to make your attacks hit as hard as possible. Choice Specs is also going to help your damage greatly. Chlorophyll doubles speed within sunny weather, and you really want to have some sort of Sunny Day setter to utilize it. The moves are meant to maximize damage to the most, while hitting a very large majority of the NU tier as neutral and super effective. SolarBeam is a must with the sun up. Hidden Power Ground takes care of Steels, Fires, and Electrics. Ice types are hit on neutral by grass moves anyways. Leaf Storm is a precious and devastating move. Grass Knot is just for anything else, as it has a shallow movepool.
For the moveset above, the reason why you don't want to choose Solar Power is because if you run a Choice Scarfed set, you only get 1.5 boost in speed, while being locked into a move, and the Solar Power increases your special attack the same as the Choice-Specs, but you even lose HP. Instead, you could opt for more speed with Chlorophyll, and Choice-Specs yourself to not lose HP.
Thanks for reading this week's POTW, I hope we can have more activity on the site!