I'm not familiar with Wittgenstein's work and I can't seem to find anything about a two seeds argument other than this review I found https://ndpr.nd.edu/reviews/wittgenstein-in-exile/

That would be the one! I'm realizing now that it's really hard to find online.

From what I understood from the quoted snippet, this thought experiment accidentally flirts with teleology. The seed is intrinsically oriented towards becoming a plant :P

Also, I'm not sure how it challenges physicalist intuition. The physicalist can argue that the seed's genetics, along with the environment, are the only variable that account for the existence of the plant.

I remember my high school philosophy classmates despairing over having to study his picture theory of language. :D (They were confused.)

What it did for me was make me realize that our belief that the seeds development into a plant must be in some way mechanical, resulting from the material structure of the seed, has no logical law behind it. That's just an intuition built up from decades of finding causes that are mechanical. Basically that physicalism has an ontological commitment that it can't prove, even aside from qualia.

The intuition isn't proven wrong so much as proven to be an intuition, something merely built up out of inference. My first thought reading it was, "But there must be!". But that's not really a must, that's just a must so long as we're wearing our physicalism-glasses; the important thing it does is show that those glasses aren't fundamentally right.

Oh I see what you mean now! Yes, you are right. It's common to default into mechanistic explanations for anything, even if it's hard. The physicalist might even call it "the hard problem of seeds"