Why do my tomatoes have brown spots on the bottom?
This brown/black spot is called BER (blossom end rot), caused by a calcium deficiency within the fruit of the plant. Utah soils have plenty of calcium, but for some reason calcium was not translocated during early fruit set. Failure to translocate calcium occurs during times of stress: transplanting, cool cloudy weather, root rot, or drought. Soil enriched with high quality organic matter reduces BER because it retains moisture while also providing aeration to roots. Mulch helps prevent BER by reducing swings in soil moisture, plus it sustains soil organic matter for good aeration.
Posted on 13 Jun 2006
Salt Lake Master Gardener