Legal Question in Real Estate Law in California

You can sue, but having done nothing about it for 16 years the landlord probably has a pretty good "waiver" defense, meaning you knowingly waived enforcement of that clause.

There's a difference between being able to sue, being able to win the suit, and, finally, coming out ahead after winning. Not only would the landlord have a waiver defense as Mr. McCormick points out, there'd be a statute of limitations defense to all claims more than four years old, and you'd need more solid proof of a breach of contract than your not seeing the gardener -- maybe he comes when you aren't there, and how do you disprove that? Finally, truly winning a lawsuit often requires proof of financial damages, collecting your judgment, paying filing fees, attorney fees, witness fees, time lost for trips to court, etc. Bottom line is that a suit for failure to perform gardener services is unlikely to be worthwhile even if there's been a technical breach of contract. A better bet is to negotiate with the landlord for satisfactory gardener services going forward.