I play a fantastic Plant/Nature controller. At 50+ and with several respecs later, I finally grasped her strengths. In Nature Affinity, the strength is understanding HOTs (heal or benefits over time) and timing.
No Corrosive Enzymes Build
As I wanted the extra slots elsewhere in my build, I didn't choose the single target Corrosive Enzymes but took the Origin Power, Mutagen, along with Envenomed Dagger from P2W. Though the dagger is not as helpful the higher level you go, Mutagen works pretty well on single targets. It may take multiple doses for some resistant or high-level targets. It’s fairly fast charging, so this isn’t a problem in rotation. Combined with Spore Cloud (the shrooms on their heads), this has worked very well to lockdown main bosses. I also didn't choose the "sleep" from Plant , as most groups or other power sets wake them up. I saved those slots to use elsewhere in the build. If someone were to make a stealth version for infiltration, sleep would be excellent for that.
Spore Cloud
This power is really helpful on tough bosses. With that said, I have other controllers who just have the Mutagen and Envenomed Dagger that help lock down a difficult boss.
Lifegiving Spores
I have this slotted with heal AND endurance, though I could see using just End. Unfortunately, my method divides the benefits of a complete set. However, the "over-time" effects linger a while after everyone leaves the circle. So, while running to the next fight, end is back up. It’s endurance replenishment isn't like KIN or ELEC, but it has been a huge help.
If you don’t like the shrooms, use the same color for the shroom as the ground to make them less noticeable.