[@Kafka Komedy][@Gentlemanvaultboy] Actually, you probably could do it with a human, if you were at least modestly careful about the sensitive areas. Contrary to what Gmvb has suggested, humans can survive mortal injuries to the heart for a while, and even recover fully from a puncture wound through the organ about 33% of the time, given appropriate medical care. And two important things to remember about JJBA are the fact that JoJo humans are pretty much confirmed to have substantially more blood than real world humans, and the timescales of JoJo protagonists and antagonists are massively warped compared to the actual passage of time - aside from anything else, DIO can apparently supply monologues and actions of a minute or two within five seconds of stopped time, and an entire car can be destroyed, the wreckage passed through, and the car then restored to its undamaged state by Josuke without the driver noticing a thing, never mind that nearly any injury at all, even headshots that ought to be instantly lethal, give the pro/antagonist several seconds of subjective time to lament and even chat about their sudden demise unless their entire head has literally exploded. In other words, it's totally feasible that Vitalogy could, for instance, tear a human's arm off, plant a seed, and have the seed grow into a brand new plant arm, and all the human would realise is that their arm is now suddenly made of tree. Even brain damage is survivable, to reasonable degrees, which could be supplemented by taking the organ apart piecemeal, say in strips of brain matter, and regrowing each section as it gets removed; maybe a couple of seconds later, their entire body is tree, and all they can do about it is scream in horror at their new tree-body. And so on.

Of course, we're not even talking about mere mortal humans. We're discussing the advantages of vampire-to-plant transformation. And I think Gmvb would be right, in that you'd end up with an entirely new species... of vampire, rather than human, since the entity you've transformed is a vampire, and they'd therefore retain their vampiric mindset, inhumanity and all. And that includes their weaknesses, too: the thing about vampires is that their dissolving into ash when exposed to the Sun isn't simply because their cells overreact to UV light, but because they literally have no soul, and are therefore held together by their own willpower rather than anything resembling life energy, with the result that life energy itself, as transmitted in sufficiently-large quantities by both the Ripple and UV radiation such as from sunlight, proves to be fatal for them. Yes, they'd be made of plant, but it'd be plant without any soul or life energy in it, and it would therefore be as weak to sunlight as before. And of course, since said plant matter needs sunlight to grow properly, transforming a vampire into a plantpire would effectively be a delayed death sentence for them as their body slowly begins to die for lack of energy... unless it doesn't because blood draining and vampire logic, I'm sure there's at least one vampire in-series with like a cactus or something fused into his face, but either way, they shouldn't gain the ability to move in sunlight just because they're now a flower human and/or vampire.