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How to Grow: Pentas
Full sun for best flowering
Bloom Period and Seasonal Color
Pentas bloom all summer.
Mature Height x Spread
18 to 36 inches tall and wide, depending on the variety.
Pentas are tropical plants that are perennials in frost free areas, but mostly grown as an annual flower across the country. They are shrubby plants in their native areas, but breeding has created a more attractive 2- to 3-foot tall flower for the garden. Their common name, star cluster, reveals the the nature the brightly colored blooms. They small, star-shaped flowers grown in tightly packed groups. The flowers are favorites of butterflies, hummingbirds and bees making this a good butterfly garden annual flower.
Penta is a sun and heat loving flower that has been bred to bloom all summer. The flowers come in white, red, pink, and violet colors with dark green leaves. It makes a great addition to a sunny, hot, flower garden. When grown en mass, the bright colored flowers put on a dazzling show.
When, Where and How to Plant
Grow pentas in a full sun location after all danger of frost has passed. Pentas love warm temperatures and will stall and not grow well if planted too early. It’s easiest to purchase penta plants from a garden center in spring. Plant transplants in well-drained, compost-amended soil. Pentas don’t like cold, wet feet. Grow pentas 1 to 2 feet apart and grow them in groups for a more dramatic effect.
Since many pentas have bright colored flowers, it’s best to grow groups of them in beds where that can be viewed from a distance such as from a walkway or road. The bright colors will make the bed pop. When viewed up close, the bright colors can be visually overwhelming. Grow pastel colored selections for containers and beds viewed up close.
Grow pentas in a fertile, well-drained soil. Amend the soil before planting with compost and, on poor soils, add a balanced organic fertilizer such as 5-5-5 as well. During the growing season, side dress additional fertilizer every few months to keep the flowers blooming strong.
Although they are somewhat drought tolerant, keep young plants well watered. Add a layer of mulch around the established plants to help conserve soil water and prevent weed growth.
Pinch the tops of young plants after planting to encourage branching and more flower formation. Deadhead spent blossoms to encourage more blooms to form until fall. Most gardeners treat pentas as annual flowers and dig up and compost them in fall. Some might try to pot up the flowers and overwinter these plants indoors in a sunny window, keeping the soil barely moist.
When grown in the right conditions, pentas are colorful, care-free annual flowers in the garden.
Diseases will effect pentas, especially when grown on heavy soils. Avoid root rot diseases by growing pentas in raised beds or in containers if the soil is heavy clay. To avoid foliar diseases don’t wet the leaves when watering but use drip irrigation.
Thrips, aphids and white flies can also attack penta flowers. At the first sign of these pests, spray with insecticidal soap to kill them. Repeat sprays every few days to kill newly hatching offspring. Spider mites love pentas, too, especially when the weather is hot and dry. To prevent damage from spider mites, mist the foliage in the morning to increase humidity. Kill spider mites with sprays of insecticidal soap.
Companion Planting and Design
Pentas love sun and heat, so plant them with other heat-loving flowers such as portulaca, verbena, lantana, and Angelonia. They’re hummingbird and butterfly magnets so grow pentas in sunny butterfly gardens along with butterfly weed, butterfly bush and salvias.
Grow pentas in containers. Select dwarf varieties and pair them with other low growing annual flowers such as dwarf marigolds, creeping zinnias and geraniums.
Grow pentas varieties based on the flower color and your garden’s location. White flowered varieties, such as ‘Starcluster White’ and ‘Graffiti Violet’ can be grown with pastel salvias, lobelias and petunias in containers and beds close to the house. Brighter colors pink varieties, such as ‘Honey Cluster Pink’ and red types, such as ‘Graffiti Red Lace’, can be used as accents in a flower garden or grouped to create a bright focal point in the yard.