In Industrial Craft 2, a crop's GGR score is its Growth, Gain, and Resistance stats, respectively. A crop's GGR score can be obtained by scanning it with a Cropnalyzer four times. This will drain an entire RE Battery however, so it is recommended to use Energy Crystals or LapPacks if you have them.
The only way to change a crop's GGR without 3rd party tools is through Cross Breeding. When two plants cross-breed, the resulting plant will have a GGR score that is between both "parent" plants' GGR. Sometimes it will also be a little bit higher or lower. Thus, to obtain high GGR scores you must go through numerous generations of crossbreeding.
The highest score for GGR is 31.
It is best to start with 4 of the plant you want in a plus-shape with an empty crossbreeder in the middle. This gives the best chance for the "child" plant to be the same as the "parents".
Using Weed-Ex on crops can potentially lower a crop's GGR score too. Thus, you should remove weeds manually if you want high GGR scores.
Each statistic has its own pros and cons.
Growth
Note: At Growth stat 24 and higher, the plant begins behaving like weeds, destroying nearby Crops. Therefore, a recommended ideal Growth stat would be 20-21, to give a reasonable comfort zone for cross-breeding.
Gain
Resist
Note: Crops can still be trampled while sneaking/crouching.
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