Q: Most of our vegetables grew very tall but with poor fruit. One tomato was ten feet tall but with only tiny fruit; cabbages grew long stems but the cabbages were size of a tennis ball. Our soil tests as high in nitrogen, low in potassium.
A: The high nitrogen test result could explain it all. Soil nitrogen encourages a plant to produce new foliage, sometimes to the exclusion of flowers or fruit. Lawn fertilizers with lots of nitrogen (like 29-4-8 or 27-0-3) exploit this phenomenon: you want your grass to grow lush and green, so high nitrogen content is preferable. Putting the same fertilizer on a tomato would result in a tall vine with few fruit.