Excessive leeching in overwatered plants leads to:

Excessive leaching in overwatered plants results in the loss of nutrients from the soil. When plants are overwatered, the water can carry away soluble nutrients along with it as it drains through the soil. This process depletes essential elements like nitrogen, phosphorus, and potassium, which are critical for plant growth and health. Without these nutrients, plants may suffer from deficiencies, negatively affecting their vigor and overall development.

In contrast, the other options suggest outcomes that are not aligned with the effect of excessive leaching. Nutrient build-up would imply that nutrients are accumulating in the soil, which is contrary to the concept of leaching. Improved soil structure would indicate an enhancement in the physical properties of the soil, which excessive leaching typically disrupts. Finally, improved flower development generally relies on a balanced nutrient supply, which would be hindered by nutrient loss due to leaching. Therefore, the correct understanding is that excessive leaching leads to a significant loss of nutrients essential for plant health.