zucchini gets about 6 inches long and starts to yellow at the blossom end
The zucchini plant itself is healthy. After the bud falls off, the zucchini starts to yellow at the bud end. This is the first year we have used this part of the yard. Could it be we need a different fertilizer? We're using Miracle Grow right now.
The problem sounds like blossom-end rot, a fairly common condition. This article should give you the information you need: https://www.gardeningknowhow.com/edible/vegetables/squash/squash-blossom-end-rot-causes-and-treatment.htm