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Series: Starla™


1. Soil and pH Needs

Pentas prefer a well-drained, humus-rich soil. Plants will tolerate light shade and drought, but will bloom most heavily with full sun and regular watering. Heavy clay soils will retard root growth and starve the plant of oxygen, which can lead to root diseases. Soil should be amended with fully composted organic matter prior to planting and in the case of clay soils the addition of pea gravel equal to at least 25% of the soil volume will aid in aeration. If adding organic matter, be aware that organic matter that has not been fully composted will tie up nitrogen and sulfur leading to nutrient deficiencies and poor growth.  Soil pH should be between 6.4 - 6.6 for optimum uptake of iron; and should be tested prior to planting but after adding any amendments. This can be done quite easily with a portable pH tester available for about $100. Mix one part soil with two parts distilled water, stir well and wait thirty minutes, then follow the instructions for using the pH meter. If pH is too low, the addition of lime is warranted. However, the rate will vary depending on how much you need to raise the pH and the type of soil you are dealing with. Clay soils or those with a lot of organic material have a high buffer capacity and require more lime than sandy soils, which have a low buffering capacity. A good soil testing lab can determine the lime requirement index (LRI) of your particular soil and can recommend types and rates of lime to use. The frequency of watering will depend on the type of soil, weather conditions and the amount of mulch. Mulch will not only reduce soil water evaporation but will also reduce splashing of water onto the lower leaves, moderate soil temperatures and reduce weed competition. Pentas are only moderately drought-tolerant and will need regular watering, especially during hot, dry weather.


2. Fertility

Pentas are moderate feeders in the landscape; and can have a crop life of four – five months. An application of a balanced controlled-release fertilizer (CRF) such as 10-10-10 or 14-14-14 with a 3-4 month formulation applied to the bed at planting will keep the plants well fed, depending on the amount of irrigation required and the average daily temperature. In areas of high irrigation and high temperatures it may be better to use a formulation with a slower release rate since higher temperatures will cause the fertilizer to be released quickly. Fertilizers that are not CRF are not recommended since the fertilizer will be leached out of the root zone long before the crop needs the nutrients. Watch for decreases in pH, if the pH drops below 6.0 iron toxicity will occur. Yellow foliage on pentas may also be caused by a nitrogen deficiency within the plant. Both can be corrected with the proper supplemental fertilizers. 


3. Disease

Water correctly to prevent most of the fungal diseases that can cause problems for pentas such as: botrytis, pythium , and rhizoctonia. Botrytis can be identified as tan spots will develop on the leaf surface, it will also infect the flowers. Established plants will show rotting in the crown. Pythium will result in damping-off with the stems at the soil line dying and the plants collapsing. Rhizoctonia attacks the stem of the plant at the soil line causing girdling and death of the tops. The best preventative is to use drip irrigation. At the very least, direct water from the hose onto the soil or mulch, and not on the plants themselves. 


White speckling is Botrytis on the flowers


4. Insects

Pentas are susceptible to thrips, whitefly, aphids and spider mites.  Thrips cause damage to the plants by piercing or sucking out the cells on the leaf surface. This causes silvery-grey spots on the foliage. At high infection levels leaves may wither. Thrips are also a primary vector for virus transmission. Aphid nymphs and adults feed on the plant sap by piercing the tissue. This slows growth and can cause leaf curling. Aphids also excrete honeydew. The honeydew will lead to sooty mold formation which will reduce growth and production. Spider mites feed on the underside of the leaves. This feeding causes yellow spots to form which results in decreased plant growth and production. Both adult whiteflies and larvae extract food from the plant. This affects the plant’s processes and results in reduced growth. Whiteflies may also transmit viruses. Remember that healthy, vigorous plants are less susceptible to pest damage than unhealthy plants.  


Aphid infestation


Foliar thrips damage


Yellowing of leaf caused by spider mite damage


Whitefly infestation on the leaf underside


5. Tips for Success

  • Deadhead spent flowers to encourage more blooms, and prune plants every so often to encourage new growth.
  • Pentas do not like soggy soil for extended periods of time.
  • Tolerates part shade, but best flowering in full sun.
  • Remove weeds from the plantings that compete with the pentas for moisture, nutrients and light.

Information provided by Syngenta Flowers