Blossom end rot is a common problem of tomatoes, peppers and aubergines grown in a greenhouse caused by erratic watering or dryness at the root.
Brown sunken spots develop at the bottom of the fruit opposite stem.
Treatment and control
General tips: Ensure the compost is kept evenly moist and not allowed to dry out. Giant Planters conatin twice as much compost as ordinary growing bags so are less likely to dry out between waterings. Pick off affected fruit and change your watering technique to applying less water twice a day, rather than an occasional flood. Feed every week with a soluble balanced plant food such as Tomorite liquid concentrate.