It's not even about the grow part, if the tenants are going to make any modifications or run something out of the ordinary like a grow op on my property it's just courteous to let me know and discuss the options. I am a landlord and I have no problem letting someone grow but would want to know that they at least had decent ventilation and not exhausting hot/humid air into say my attic which could long term cause damage. Anyone who defends a renter doing whatever the f*ck they want with a rental has never owned property. And there are clauses in my rental contracts that require them to inform me of any modifications to the use of the property for anything other than the stated rental of the property as a place of residence. Basically it's a catch-all so that if I do get some a-hole venting into my attic they've broken the contract and I can boot their asses out. The tenant signing that contract with the clauses gives me the right to refuse them to grow, and if they hadn't given me a heads up I'd give them the boot for being a-holes if nothing else.