I'm growing my zucchini's in two tires stacked with very good soil from decomposed cow poop. The plants look great and are growing and having tons on flowers and zucchinis coming on. I have harvested three gorgeous zucchinis, but now the little guys are rotting before they get two to three inches long. I have the watering on a timer for 15 min every 6 hrs. The soil stays moist. The irrigation comes from a soaker, not spray. My other squash in a second container (hubbard, acorn, and butternut), have tons of melons and no rot yet. I have not fertilized at all. What should I do? Thanks.