Key things to know:
- The better your seed's rank (quality + traits), the rarer the items you get.
- Seed grown items may have effects, such as Synth Quantity +1 or (Element) Lv. +2, and so on.
- The traits you get are determined by the traits on your seeds. For the highest grade traits, you need to use seeds with traits that have at least 50 grade. What's grade? A hidden value every trait has; the values are listed here.
- Need more greenhouses? Grow more seeds. I didn't count, but it should be less than 20 for all four. Story progress matters also.