| First check whether your Calla is a Zantedeschia aethiopica or is it an other variety. As a rule of thumb Zantedeschia aethiopica requires lots of moisture and will not rot even if submerged but the other varieties such as Zantedeschia rehmannii, Z. elliottiana and Z. albomaculata require a well drained medium and will rot if there is much moisture. just google the names i mentioned and you will get to know, which is your plant.. hope it helps..!! Izhar | 
