My white patty-pan squash get about two inches across and then dry up. Please tell me what causes this and what to do for it. When you read the garden books and often the news articles taken from the national news services, you will read that blossom-end rot is due to a lack of calcium. Gardeners familiar with New Mexico's soils realize that our soil is not deficient in calcium and wonder how they could get blossom-end rot. The answer is that though we have an excess of calcium, we have a deficiency of water and extremely desiccating environmental conditions.
Calcium travels through the plant in the water.
Dry soil, hot, dry, windy days, or anything else that prevents water from reaching all parts of the plant can limit the movement of nutrients in the plant. Hot, dry, windy days, or a brief period when the soil drys disrupts the flow of water and nutrients through the plant. When this happens, the small developing fruit loose their supply of water and calcium. As the fruit enlarges, the brief deficiency of water and calcium becomes apparent as blossom-end rot. Dr. George Dickerson, Extension Horticulture Specialist for vegetable crops, small fruits, and speciality crops, suggests that care be taken to keep the soil evenly moist and the use of mulches to reduce the evaporation of water from the soil.