Ann, that is interesting and certainly worthy of deep thought and care.
In one of my seed catalogues this company advises when growing the big sunflowers for seed heads to dissolve a little boron in some water and feed the plants, I think they may need only a tiny little bit. And I think it was like 1 tsp per cup, giving each plant only a tiny bit of this. I would have to revisit their instructions though for stronger remembering. Evidently the sunflowers use alot of boron to grow strong to build good flowerheads. I haven't ever used it because I am too lazy, but it is worth some thought I would imagine, but surely, one would have to be careful of how much went into the soil for sure. Have a wonderful day, great life on this great earth. Cindi