Isotoma axillaris ( Eye-SOT-oh-muh ax-ILL-ar-iss) is an Australian and New Zealand native.
It does very well in warm climates in USDA hardiness zones 10 – 11. It grows as a perennial but does well in cool climates when grown as an annual.
Isotoma axillaris is also known as Laurentia (law-REN-tee-uh) and also Solenopsis (sol-en-OP-sis) axillaris. You may sometimes see this classification used in plants for sale.
It also has other common names which include:
- Rock Isotomes
- Blue Star Laurentia
The Greek word ‘isos’, means equal and ‘toma’ meaning section. This name describes the equal segments of the corolla of the plant.
Isotoma Axillaris Care
Size & Growth
These plants grow 12″ to 15″ inches high with an equal width in a compact mounded manner.
Flowering & Fragrance
The plant produces an abundance of pretty, fragrant, star-shaped flowers rising above the foliage. Blue Star blooms from June until the first frost.
Bloom time varies depending on climate. In very hot, muggy locations the best bloom time may be from May through July.
Flowers are large and showy and generally range from an inch to an inch and a half wide.
Although the blue variety (Beth’s Blue) is the most common. The plants are also available with violet, white or pink blossoms.
Interesting and exciting hybrids such as White Star, Starshine Blue, Starlight Pink and Sophia add color and variety to your Laurentia collection.
The foliage has medium green leaves, long and fern-like. They grow from a woody base on branched, upright stems.
Light & Temperature
Starflower likes to be grown in full sun (6 hours of sun daily or more) but also does well in partial shade. In the United States, this plant is only winter hardy in USDA hardiness zone 11.
Watering & Feeding
As long as you plant in well-draining soil, the Blue Star can do well with dry to moist soil.
Fertilize monthly throughout the growing season using a balanced water-soluble fertilizer or an organic fertilizer (e.g. fish emulsion). Follow packaging directions carefully.
Soil & Transplanting
Laurentia prefers well-drained soil and full sun. The plant thrives in humus enriched, well-drained soil and does well tucked into rocky crevices.
Grooming & Maintenance
There’s no need to deadhead these plants as they shed flowers as they die out. You can shape the plants and encourage more blossoms by pruning in midseason.
Laurentia Axillaris Plant Propagation
You can grow Laurentia from seed by sowing them indoors very early in the season approximately 10 to 12 weeks before the last frost.
It takes around four months for the plants to mature and be ready to flower.
Start seeds in early February or sow seed directly into the ground later in winter after all danger of frost passes.
Alternately, take cuttings from plants in the fall and start them indoors through the winter to have them ready to transplant outdoors in the springtime.
If you keep Laurentia as a container plant, overwinter them indoors.
They do well in a sunny yet cool location. Reduce water while overwintering plants. These plants are also readily available in most nurseries in the springtime.
Pest or Disease Problems
As with most plants, provide ample room for ventilation and do not overwater, you are unlikely to have problems with pests or diseases.
Compromised plants may be bothered by mealybugs or aphids.
Starflower is both deer and rabbit resistant.
The Australian National Botanic Gardens also report that the plant is resistant to predation by insect pests and marsupials.
Are Laurentia plants considered toxic or poisonous?
The sap may be irritating to the skin. Be sure to wear gloves when working with this plant and wash up thoroughly when you are done.
Is Isotoma Considered Invasive?
Because this plant is only winter hardy in USDA zone 11, it is not generally considered invasive in the US. Remember it is an Australian/New Zealand native.
If your area has hot, dry weather that mimics the Australian and New Zealand climate, keep an eye on it and don’t let it get out of hand.
Suggested Uses For Isotoma Axillaris
Laurentia is an excellent choice as a border plant, and it also does very well in containers.
This low-growing plant is a good filler in the flower garden and for softening the edges along paths or flowerbeds.
When planted densely it makes a good groundcover. Its growth habit allows it to spillover freely.
It’s also a good choice for hanging baskets or to ornament rock walls.