"I'd wanna," and here he pauses to shift and bite his lip, pulls out his lighter and flicks it on and off while he thinks of the right word, "supervise, or whatever. If you look through the seed banks."

It's not that he thinks Severus is going to steal away seeds, or is particularly untrustworthy. (Not that he thinks Severus is to be trusted, either - so far his impression has been on the positive side of neutral.) It's that ned himself is particularly untrusting and has a few. Issues. When it comes to possessions and the Gardens, both. Oops.