He openly told the police that he had them. That's like telling them that your neighbor is making crank.
They'll watch the house, and the traffic until they can obtain a search warrant. If they legally obtain a search warrant then there's nothing he really can do. He should not have told the officer's in the first place. Also he should not have let them on the premise's. From your story it sounds like they knew the plants were there, and were trying to get pressure him into letting them in. If anything you might be able to "motion to suppress" on the search warrant, but it depends on what the warrant says for reasoning for it's issuance. If it was initially because of his statements, maybe (big maybe) you could win it. The confession could be called hearsay, but they did find plants on the premise's. You're going to need a good lawyer to get him out of this one.
