I suggest using Grade 3 Shroud soil for Krakka crosses only, for both the Krakka and the seed you are crossing with it. You only have a 10-20% chance of getting the seed you want, but you will get 9 at a time on top of the extra Krakka roots.

If you are making Thav Onions, the ideal 3 bed grow-op is:
  1. Glazenuts x Apricots (grade 3 than soil) -> Glazenut Seeds
  2. Glazenuts x Pahsana (grade 3 than soil) -> Apricot Seeds + Thav Onion Seeds
  3. Thav Onions x Linseed (grade 3 shroud soil) -> Pahsana Seeds + Linseed
When you have Pahsana Seeds and Thav Onion seeds built up, swap out the Linseed in the 3rd bed with onions and make a full bed of Thav Onions.

This setup is self-sustaining as long as you have about 20 Glazenut and Apricot seeds built up. Both will dip down at times based on RNG, but long term you will have enough.