Disciplining a toddler-baby

So these days with Oliver can be trying to say the least! He is most definitely no longer a baby but I'm hesitant to label him as a toddler just yet... not least because he is not yet walking but also, in my mind toddlers have a more obvious understanding of what you're saying. At this age it's near impossible to tell whether they understand you or not, sometimes I think that Oliver does (whether he listens or not is another thing entirely!) and others I think he just doesn't have a clue!

The difficult thing is... how do you discipline them? Should you even be doing so? I am sure the word 'No' is understood fairly early on (whether they admit it or not) but how much do they really understand?

Oliver has developed an obsession with a plant.

This plant.

Yes, that mess of soil on the carpet is a remnant of one of his previous encounters with it! He throws the soil out, eats it, rips the leaves off, eats them... etc. etc. I promise you, I'm doing everything those darn parenting books say... I say "No!" firmly, I move him away, I find a distraction. I repeat this process incessantly but he keeps coming back. To be honest it is not often an issue because it's in a room he doesn't normally have access to but if I happen to be in here.... trouble is soon afoot. Besides it's not just about the plant, it's about laying good ground rules right? Or should I just 'chillax' about the whole thing, he's only one after all?
Any ideas??

(PS - no suggestions of any physical discipline please, it might work for some but it's not for me!)