Calibrachoa (Calibrachoa x hybrida or Calibrachoa group) split from the petunia family (Petunia group) in 1989, but the two plants share similar needs for water, soil and temperature. Also called seashore petunia, trailing petunia or million bells, calibrachoa is a somewhat smaller plant with smaller flowers than a petunia. Calibrachoa grows in mounds 3 to 9 inches tall or as trailing stems about 20 inches long, while petunias grow 10 to 14 inches tall and spread 2 to 3 feet wide. Calibrachoa grows in U.S. Department of Agriculture plant hardiness zones 9 through 11 and as an annual elsewhere.
As a general rule, water petunias once a week with a thorough watering to promote healthy roots. Petunias prefer soil that is evenly moist, yet well draining as damp soil causes root rot. Wait until a top inch or 2.5 cm of soil feels only slightly moist before watering petunias again with a generous soak.
