So I'm testing .71 on a copy of my server and ran into what might be a bug.
Netherwart can only be planted (using crops) on soulsand but waila says it can't grow there. Waiting 10 minutes didn't yield any growth ticks so I think waila is correct that it won't grow.
I tried to plant nertherwart on tilled and untilled dirt and garden soil as well and it won't place so I'm guessing souldsand is correct but there is a bug not letting it grow.
Netherwart only grows in dark places and in soulsand, so.... back a black room for it!
They can be boosted from the same plant or from the plants that you used to generate the seed(the parent ones). So... after you cross bread a plant, keep maxing it out with the one you used to cross breed.That can only be boosted from the same plant/seed type now. If you are using the same type then I'm not sure.
I would always go for a full 10/10/10 so later I dont have staking problems with different strengths. If you already maxed the two others, strength would be at like 8 or 9, so it doesnt take much to get it to 10 toooh. so that means im done with pumpkins