Pentas are a tropical import, and grow wild in East Africa. Plants are just the right size for the middle of the summer border: the average height of pentas is 24–36 inches, but plants that perennialize in frost-free zones may reach four feet tall or greater. The dark green foliage of pentas plants is slightly fuzzy, and the five-petaled blossoms grow in three-inch clusters similar to other butterfly favorites like sedum, lantana, and Queen Anne’s lace. Blossom colors include pink, purple, white, and red. Penta plants can stay in bloom continuously under ideal growing conditions, so it’s worth a bit of weekly care to keep the plants in optimum condition.
Many gardeners choose penta transplants to start in the garden, but you can try planting fresh pentas seed saved from last year’s flowers, or start softwood cuttings taken early in the growing season. Penta seeds require light to germinate, so don’t cover them with soil.
Penta plants that receive at least three hours of direct sun will have the best blooms. Plants that don’t receive enough sunlight will stretch and become leggy. Plants prefer full sun, although some afternoon shade is tolerated.
Pentas appreciate a mildly acidic soil pH in the range of 6.0. Amending the soil with compost or leaf mold can increase the acidity of your soil if it’s on the alkaline side.
Pentas need regular irrigation to stay healthy; keep the soil moisture about the same as a wrung-out sponge. Pentas tolerate dry conditions, but drought-stressed plants are susceptible to spider mite infestations. Avoid regular overhead watering to prevent unsightly brown spots on the foliage.
Temperature and Humidity
With their tropical origin, Egyptian star clusters love heat and humidity and thrive in warm climates.
Fertilize pentas once a month with a balanced flower fertilizer during periods of active growth. Timed release fertilizers are ideal, and will nourish plants throughout the growing season. A greater phosphorus content will encourage blossom formation, while nitrogen fosters leafy growth.