To start with, while I was in the process of obtaining various berries, I was directed to a certain Reddit thread where this wondrous infographic with just about everything you could want to know about berries in Gen6 was posted.
To start with, you will need the following berries (and where you can find their trees):
- Oran (route 5)
- Pecha (Camphrier City)
- Tanga (route 22)
- Yache (route 19)
- Aspear (route 12)
- Leppa (route 15)
- Aguav (route 6)
- Figy (route 21)
- Roseli (route 14)
- Kasib (route 20)
- Mago (route 8)
- Iapapa (route 10)
Now, a new aspect to berry farming in generation 6 is mutation. When two different berries are planted next to each other, there's a chance that the resulting bushes will contain one or two mutations; a 'new' berry. This only works for specific combinations of berries, and the chance for mutations can be drastically increased by using Surprise or Amaze Mulch (although Amaze requires composting the two berries you are after).
For the following steps you are going to want a minimum of ~20 bags of Surprise Mulch (Assuming we're only growing one of each plant until the two target berries), which means mulching something quick and cheap like 3 Oran berries seven times.
- Plant Each of the following pairs in mulched locations right next to each other:
- Oran and Pecha (result = Qualot)
- Aspear and Leppa (result = Hondew)
- Aguav and Figy (result = Grepa)
- Mago and Iapapa (result = Pomeg)
- After we harvest those, we pair the results with our remaining starting berries. Plant the following pairs in mulched locations right next to each other:
- Qualot and Tanga (result = Ganlon)
- Hondew and Yache (result = Liechi)
- Grepa and Roseli (result = Salac)
- Pomeg and Kasib (result = Petaya)
- After we harvest the results of step 2, we pair those off in mulched locations right next to each other:
- Ganlon and Liechi (result = Kee)
- Salac and Petaya (result = Maranga)
- Now you just start farming berries until you feel you have a sufficient supply.