Sandys Nursery Online Plumbago Imperial Blue Gallon This Fast-Growing Perennial Shrub Has Bright-Green Foliage Accented with Sky-Blue Flowers Throughout the Year. Amount of Water: Water Regularly; More Frequent Watering In Extreme Heat; Moderately Drought Tolerant. At maturity they can reaches 3-4 Feet Tall (2-3 Feet Wide). Ships: (1) Gallon Pot with soil.