Pentas, a genus of plants from the Rubiaceae family, which includes coffee plants and gardenias, is indigenous to the Arabian Peninsula and tropical and semi-tropical Africa. Commonly called starflower or star cluster or Egyptian starflower. They grow as annuals in temperate areas but often become perennial in warm climates.
The lance-shaped leaves are dark green, about 6 inches in length, and slightly fuzzy. They usually grow to around 18–36 inches, but perennial plants growing in their natural habitat or warm and frost-free climates can reach 3 – 6 feet high. If the climate in your area is frosty and cold in winter, it would be better to grow the plants in containers that can be brought indoors as they will die back if exposed to frost.
These plants grow as shrubs and appear to be specifically aimed at attracting nectar-loving butterflies, hummingbirds, and bees to their nectar-rich flowers that grow in clusters during their blooming season from spring until autumn and even winter in hot climates. The colors of the flowers range from red, white, purple, magenta, and pink are like beacons to butterflies. The flowers are shallow and easy for pollinators to access. New varieties have been developed with better disease resistance, more compact growth habits, and new variations in color. Some species like P. lanceolata can tolerate full and direct sunlight, need very little care, and can grow in hot and dry climates.
Adding this plant will make your garden busy with activity, and along with other flowering plants such as butterfly bush, lantanas, salvia, and marigolds, your garden will turn into a riot of color, attracting beneficial insects that will help pollinate other plants in your garden. Pentas do well in both the ground and containers, and can even grow indoors provided they get sufficient light. These plants can bloom continuously if provided with ideal growing conditions, although it’s worth making a little effort to care for the plants to keep them growing in optimal condition.
They can grow under partial shade but prefer an area that will get full sun or a minimum of 6 hours of bright sun every day. When planting multiple plants, space them out around 18 – 24 inches between each other to prevent overcrowding. Plants that grow under insufficient lighting conditions tend to get leggy and produce less or faded flowers, taking a long time to recover.
Water the plants when 1 or 2 inches of the topsoil is dry as they grow best in moist soil. Keep a watch on your watering schedule as these plants might need extra watering during the hot summer months although they are considered to be moderately tolerant of drought. In addition, do not water the plants overhead as this can cause damage to the foliage – water the soil around the plant’s base.
Adding mulch will help retain moisture as spider mites often infest the plants when they become too dry.
Over-watering and under-watering these plants have almost the same effect on these plants resulting in brown leaf edges, sagging leaves, a sallow or yellow leaf color, and stop flower production including root rot. Proper drainage is necessary to avoid over-watering, particularly if growing the plants in containers.
These plants thrive with high humidity. Growing them indoors will require a humidifier or raising humidity levels by misting the leaves frequently, without wetting the buds or flowers.
While they are heat tolerant, try to maintain temperatures between 70 – 75°F in the day, with night temperatures between 55 to 68°F. They are intolerant to frost and need special care in places with temperatures 20 – 30°F and are not likely to survive temperatures below 20°F.
They prefer loose and well-draining somewhat acidic soil. You can amend the soil or create a mix of 40% compost, 40% sand, and 20% soil to increase acidity if the soil is alkaline.
Repotting these plants in temperate areas is usually done in spring and throughout the year in warmer areas. Select a container or pot 2 – 3 inches larger and with good draining capacity. Partially fill it with appropriate soil. Carefully take the plant out of its previous home and insert it into the prepped container, filling in empty spaces with soil to hold the plant in place. Water it well when you’re done.
They can be easily propagated by cuttings or seeds although propagating from cuttings is easiest.
Propagation from seeds
This should be done inside your home 2 months before winter begins or the first frost is predicted or outdoors in warm climates. Prepare a seed starter tray of individual cells and fill it with appropriate soil. Place the seeds on the soil and expose them. The seeds need light and darkness to germinate, so seeds started indoors should not be placed under grow lights for 24 hours – following the natural cycle of the day. Mist the seeds lightly every day until shoots emerge in 2 – 3 weeks. They can be transferred to pots once two sets of real leaves have formed. Seedlings grown indoors need to be slowly hardened by taking them outdoors in the day and back indoors at night before you move them into your garden in spring.
Propagation by cuttings
Start by preparing small pots filled with 1 part perlite and 1 part moss. Take healthy-looking cuttings, remove the last two leaves, and dust with rooting powder. Use a pencil or something similar to make holes in each pot, pushing the cutting in and firming the soil around each cutting. Place the cuttings under a shaded spot with indirect sun and away from the wind. They should start rooting in 2 – 3 weeks.
Fertilize the plants once monthly with a fertilizer specifically meant for flowering plants. Slow-release fertilizers applied in spring are ideal and will nourish the plants throughout the year. A fertilizer with more phosphorus will encourage flower formation, while more nitrogen promotes leafy growth instead.
To promote bushy growth, cut off stem tips. Prune away damaged or dead stems in winter before spring. Deadhead spends flowers and removes dead and untidy stems as careful pruning will help keep the plants healthy to produce more flowers.
In temperate or cold climates, save your outdoor plants from winter by transplanting them into containers and bringing them indoors. Place them in a warm room with no drafts and sufficient bright light. Reintroduce them gradually outdoors in spring when ambient temperatures reach 65°F.
These plants can experience some problems with pests like aphids, spider mites, fungus gnats, and whitefly. Control light aphid infestations with a powerful spray of water. Fungus gnats, spider mites, and whiteflies can be controlled with insecticidal soap or neem oil.
A fungicide containing copper will help deal with botrytis blight, mildew, and leaf spots. These can be avoided by watering the soil directly and not getting the foliage wet. Remove affected leaves to prevent the infection from spreading.