Berry farming is way too easy and not grindy enough for an MMO environment
my suggestion is to implement a feature where you have to use a fertilizer to make your berries grow,
and this fertilizer is made by grinding together 12 thick clubs using a special machine.
To access this special machine you must have permission from the Berrymaster.
To get permission from the Berrymaster you have to complete 20 quests for him.
Each quest will involve either finding a set number of items or defeating a certain number of pokemon.
You can only complete 1 quest per day.
Quest difficulty increases the more you complete them.
The Machine itself is powered by shards.
The amount of shards you give it determine how effective it is.
The less shards you give it the higher the change the machine might not make the fertilizer
The following chart compares the number of Shards inserting in the machine and the chance of failure
(note number of shards means each one. ex 10 shards means 10 Red, Blue, Yellow, and Green)
10 Shards = 90% chance of failure
20 Shards = 75% chance of failure
30 Shards = 50% chance of failure
40 Shards = 25% chance of failure
50 Shards = 1% chance of failure
(note it is impossible to gurantee 100% success so keep that in mind when using Shards)
Then if all goes well then you have your fertilizer and can start growing those berries :)