What is the ruling on placing flowers and plants on graves, and is the Hadith of the palm branch used as evidence for its permissibility?

The issue can be summarized as follows: the hadiths concerning the placing of two palm branches on the grave have led to a wide disagreement among scholars regarding their intended meaning and purpose. Some believe that the alleviation of punishment is temporary, lasting only as long as the branches remain moist. Others are of the opinion that it was specific to the blessing of the Prophet's hand (peace be upon him). Still others believe that it is not exclusive to palm branches but includes anything moist, or that it was an intercession from the Prophet (peace be upon him).

Some scholars have inferred from this the permissibility of planting trees and fragrant plants on graves, while others have rejected this. The preponderant view is that it is not prescribed (non-permissible) and that it was a unique characteristic of the Prophet (peace be upon him), because he foretold the alleviation of punishment through his intercession. The fact that the grave's occupant is being punished is a matter of the unseen, and it is more befitting to focus on benefiting the deceased through charity and supplication.