Pentas Flowers, the Egyptian Star Cluster

Pentas, Egyptian Star Cluster
Photo: Josie Elias/Getty Images

Pentas plants are semi-tropical shrubs grown as annuals that seem to be tailor-made for butterflies. The nectar-rich flowers grow in clusters over a long blooming season in the vibrant red, pink, and purple shades that act as a butterfly beacon. Clusters of many shallow blooms provide an easy access for the butterfly proboscis, allowing the insects to dip into many flowers in a short period. Bees like them too, so consider adding this plant to a landscape space you want buzzing with activity.

The genus Pentas, species lanceolata, belongs to the Rubiaceae family, which includes other beloved ornamentals like gardenias, as well as plants with economic importance like coffee. You may see pentas described on plant tags by the common names star flower, Egyptian star flower, or star cluster. You can grow pentas anywhere as an annual; in growing zones 9 and warmer the plants may even perennialize.

Get to Know the Egyptian Star Cluster

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 3-inch clusters similar to other butterfly favorites like sedum, lantana, and Queen Anne’s lace. Blossom colors include pink, purple, white, and red.

How to Plant Pentas

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. 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. Pentas seeds require light to germinate, so don’t cover them with soil.

Care of Pentas

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. 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.

In frost free growing zones, pentas will exhibit their shrubby nature and begin to grow leggy after one growing season. Prune the plants to six inches in January, when bloom production is at its lowest. After several seasons, the stems of the pentas may become so woody that it’s worth replacing them altogether. When growing as an annual for one season, no pruning is necessary, but regular deadheading will keep the plants blooming productively.

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. 

Garden Design Tips With Pentas

Pentas thrive in containers or tubs, and they also look cheerful in the ground combined with other hot weather lovers. You can plant pentas alongside other vivid butterfly annuals, like zinnias, marigolds, cornflowers, or gomphrena.

Gardeners with high indoor light levels can try their luck at growing the pentas as a houseplant, but whiteflies may plague plants grown indoors. Bring plants indoors before the first frost, or take cuttings from desired varieties. A cool room with bright light is an ideal spot to overwinter plants. Keep indoor plants vigorous by adding a supplementary light source, and by increasing the humidity with a gravel and water filled tray. 

Pentas Varieties to Try

New pentas cultivars feature disease resistance, as well as dwarf forms suitable for border edges and containers. The ‘Butterfly’ series is easy to grow from seed for gardeners who want to populate a large flowerbed on a budget. The ‘Graffiti’ series features compact mounding plants with large flower heads. ‘Kaleidoscope Appleblossom’ pentas are early bloomers with pale pink and rose on the same flower. Gardeners in rainy areas can succeed with the ‘New Look’ series, which produce upright plants that don’t flop. If your growing season is short, try ‘Northern Lights’, which continues to produce pale lavender flowers in cool temperatures.