Pentas Flowers, the Egyptian Star Cluster

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

Pentas 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. Bees like them too, so consider adding this plant to a landscape space you want buzzing with activity.

The genus Penta, species lanceolata, belongs to the Rubiaceae family.

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

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 penta 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

Full sun is preferred, although some afternoon shade is tolerated. Plants that receive at least three hours of direct sun will have the best blooms. Pentas that don’t receive enough sunlight will stretch and become leggy. 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 penta 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.

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.

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 penta as a houseplant, but whiteflies may plague plants grown indoors.

Pentas Varieties to Try

  • ‘Butterfly’ series: Easy to grow from seed
  • ‘Graffiti’ series: Compact mounding plants
  • ‘Kaleidoscope Appleblossom’: Pale pink and rose on the same flower; an early bloomer
  • ‘New Look’ series: Upright plants that don’t flop
  • ‘Northern Lights’: Continues to produce pale lavender flowers in cool temperatures