I think there's a couple of lemon trees growing across from the Shrieking Llama in Windenburg.
Also, if you have City Living, you can buy pretty much all the produce (including pomegranates) from the produce stalls.
As far as the original question, yes, I've gone all the way through the process of growing a death flower, for the goal of reviving a vampire that I had re-added to his household as a ghost. By the time he achieved the capability and ingredients to cook the ambrosia he seemed really comfortable as a ghost vampire so I've just let him be. :P He currently has 67 death flowers in his inventory so I'm going to have him plant some around the neighborhoods.