You must aim for x/x/x/30/31/31.
1. x/x/x/x/x/31 + x/x/x/x/x/x = x/x/x/x/x/31 (1:4)
2. x/x/x/x/31/x + x/x/x/x/x/31 = x/x/x/x/31/31 (1:17)
3. a) x/x/x/x/31/31 + x/x/x/30/x/x = x/x/x/30/31/x (1:17)
or b) x/x/x/x/31/31 + x/x/x/30/x/x = x/x/x/30/x/31 (1:17)
4. a) x/x/x/30/31/x + x/x/x/x/31/31 = x/x/x/30/31/31 (1:54)
or b) x/x/x/30/x/31 + x/x/x/x/31/31 = x/x/x/30/31/31 (1:54)
5. a) x/x/x/30/31/31 + x/x/x/30/31/x = x/x/x/30/31/31 (1:29)
or b) x/x/x/30/31/31 + x/x/x/30/x/31 = x/x/x/30/31/31 (1:29)
or c) x/x/x/30/31/31 + x/x/x/x/31/31 = x/x/x/30/31/31 (1:29)
6. x/x/x/30/31/31 + x/x/x/30/31/31 = x/x/x/30/31/31 (1:16)
About every 16th baby will now have a chance to have Hidden Power GRASS with base power at least 65, if any one of the following holds:
* HP IV is an even number, Attack IV and Defense IV are odd numbers
* Attack IV is an even number, HP IV and Defense IV are odd numbers
* Attack IV is an odd number, HP IV and Defense IV are even numbers
* Defense IV is an even number, HP IV and Attack IV are odd numbers
* Defense IV is an odd number, HP IV and Attack IV are even numbers
This means that the highest IVs you can have for Hidden Power GRASS are either 30/31/31/30/31/31, 31/30/31/30/31/31 or 31/31/30/30/31/31.
Note that if you want either Hidden Power ICE or Hidden Power GRASS, you can breed a x/x/x/30/31/31 parent with a x/x/x/31/31/31 parent.