Without knowing the details of your planet, my first response is to say that Farming is always the better option for an intelligent species, whether they are herbivores, carnivores, omnivores, detrivores or any other form of consumer of organic matter.
Let's start with the most obvious reason; supply. Farming doesn't guarantee a steady supply of food, but it's certainly a start in that direction. Sure, there can be droughts, blights, infestations and other interruptions to crops but generally speaking, farms allow a species to produce food en masse allowing for the bulk of the population to worry about other matters.
As elemtilas has explained in his answer, the fact that we're talking detritus complicates the 'harvesting' process but there's a very good reason to overcome this problem, which is that agriculture allows for a much smaller percentage of the population to be focused on food gathering or production. This frees a larger percentage of the population to focus on metallurgy, science, monument building (which means engineering), transport (the wheel), defence, and other pursuits. This in turn generates a diverse economy and with it the need for leadership, which in turn means that leaders rise who can focus the collective effort towards that which benefits the whole, not just the individual.
Without farming, you don't get things like land ownership, economic theory, scientific advancement, rule of law, and even protection from minor food supply anomalies.
Sure, farming is labour intensive, but it's that intensity which frees up the rest of the population to focus on broader and more diverse pursuits which allow them to advance their civilisation beyond simple hunter gathering.