How can you get your friend in trouble?
Well, since you are being paranoid, seeds are classified the same as leaf and bud under federal and most state law. Seeds are cannabis under most state regs. Even here in MA, which is rec legal, seeds are classified as cannabis.
At a minimum, if a leo was attemtping to be prickish, that could lead to a possesion charge, If they really want to squeeze them (to flip the grower), they can add sending/receiving controlled substances through the mail. They can completely toss the guys house, and if he has any loose weed or other contraban, they can up the charges. That could cost him/her a job, a professional license, or potentially, custody of kids. In the 1980's under ronnie raygun, houses and yacht's were seized/forfeited over a single joint.
So yeah, there are risks. Realistically, it's such a low priority that it is a joke to most leo's.
Unless you are in iowa, wisconsin, or a state that is trying to profit from drugs. It is common in those states for leos to search your phone. They have rippers they can use even if you won't unlock them (may not work on all phones, but it works on a lot).
So, just stay in the herd, don't stick out, don't call attention to yourself, and don't have a significant other. It seems pissed off ex-lovers are a very risky loose end.