With origins in tropical east-central Africa, the pentas or star cluster (Pentas lanceolata) grows as an evergreen perennial with woody lower stems where winter frosts never occur. In the U.S., pentas is grown as an annual during the heat of summer and dies once fall frosts arrive. The tiny five-petaled flowers develop in domelike clusters on stem tips, attracting bees, butterflies and the occasional hummingbird.
Pentas plants need ample sunlight to produce flowers, so place them in full to partial sun locations in the garden. The soil must be fertile and moist, but well-drained. Pentas roots rot when suffocated in soggy or flooded soil. When basking in warmth and lots of sunshine, pentas plants respond favorably to lots of water and fertilizer. However, if grown indoors or in a tropical region, keep the soil drier in the winter when the sun rays are weaker and temperatures cooler.
The effects of overwatering a pentas can look deceivingly similar to an underwatered plant. Symptoms of overwatering include brown leaf edges, downward or sagging leaves, an overall sallow or yellow leaf color and a cessation of flower production. Touching the soil around the base of the pentas reveals insight as to soil moisture. A wet or cool, spongy soil suggests overwatering. However, a dry soil surface can mask any soggy soil inches below that arise from poor drainage.
The hotter and more sunlight a pentas plant receives from spring to fall, the more water it needs. Keep the soil evenly moist. Sandy soils need more frequent watering than the heavier textured loam or clay soils. It's much more difficult to overwater a pentas in a sandy soil than clay soil. If planting pentas in a hanging basket or container, make sure drainage holes exist. Sitting water rots roots, leading to plant stress and eventual death.
Allow the wet soil conditions around sick pentas plants to dry out to slightly moist. Monitor the health and vigor of the plants as the wet soil changes to a more conducive level. Do not arbitrarily water pentas plants, but only once the soil surface feels slightly dry to the touch -- a fingertip will have some particles of soil stick to it when the soil is slightly dry. If soil is always rather moist, reduce watering or remove mulch to allow better air circulation to offset overly damp conditions.