look here: http://forum.industrial-craft.…page=Thread&threadID=4004
There is the list of most IC plants. 2 plants have only small chance to produce different(mutated) child, but high tier parents have higher chance to produce high tier children. So basically it's best for you to try to crossbreed two Tier II plants, like rose and dandelion, reed and reed, reed and melon, to get best results. If you got some cocoa, it is smart to plant some too, as it's Tier III plant.
Just set up 10 [P][CB][P] fields, where [P] is parent plant and [CB] is crossbreeding block created by placing cropsticks on empty cropsticks.
Also don't forget to fertilize and hydrate parents and even empty cropsticks and stay close to quickly react when weed appears.
Happy farming.
Thanks