Crossbreeding from 4 plants would randomly choose two of them to be the parent.
Stats are based on parent stats +-2. Thus you can get better or worse plants. Separate the goodies, plant them again and repeat until you have crops with decent stats.
Note that crops with high stats need good environment (or cropmatron fertilizer and hydration aid).
Ok I'm using a cropmatron to fertilize. But do I still need to use hydration aid as the plot is always wet with water nearby?