A traffic stop leads to a driver's arrest because of marijuana plants in the vehicle. Is this alone (presence of illegal marijuana plants in the car) probable cause for a search warrant of his house?
No admission was made as to where the plants or vehicle came from. When asked, the driver denied "if anything illegal would be found at his residence," nor was consent given to search his residence. Neither he, his vehicle or residence were under investigation.
Apparently the possession of marijuana plants is illegal wherever this incident occurred, or the traffic stop would not have led to an arrest for that reason. The fact that an arrest was made means that the police officer(s) found reason to justify an assumption of probable cause that a crime had been committed because "an officer may not arrest a person until the officer possesses probable cause to believe that the person has committed a crime."
It would be up to the court to determine if probable cause to justify issuing a search warrant of the person's home was present. The decision would be influenced by the behavior of the suspect - if s/he appeared to be under the influence of marijuana at the time of the arrest, that might be seen as supporting a search warrant. The fact that the suspect, the vehicle and the residence had not been under surveillance prior to the arrest might be seen as an argument against granting a search warrant.
Courts take care to review the actions of police in the context of everyday life, BALANCING the interests of law enforcement against the interests of personal liberty in determining whether probable cause existed for a search or arrest.
There would be too many variable factors involved to be able to give one final and always correct response to your question.