Its a simple farm, that uses 8 hoppers to collect all the drops from a tall flower when bonemeal is added by a dispenser.
Any clock will do for the dispenser. this is just one example.
The hoppers must be placed to direct the items to a chest, so you can easilly retreive the items.
Add bonemeal to the dispenser.
The glassblock on top is to make sure no items land on the dispenser.