Blue star creeper (Isotoma fluviatilis) is a low-growing flowering perennial that is adorned with delicate pale purple to blue star-shaped flowers from late spring into late summer and early fall. It has gradually gained a foothold as a groundcover substitute to turf grass in moderate climates, but is also sometimes planted as a bedding annual in colder regions. This Australian native has a spreading and mounding growth habit, forming a dense, low mat of leafy green foliage that holds up well to moderate foot traffic. It requires less water than a traditional grass lawn, and it grows to just 3 inches tall, requiring no mowing. It is impressively tolerant of extreme weather conditions and even tolerates short drought.
Blue star creeper is generally planted from potted nursery plants in spring, and will quickly spread through runners to blanket sunny areas. Individual plants reach full size in a single growing season and will begin extending runners in their second year.
|Common Name||Blue star creeper, swamp isotome|
|Botanical Name||Isotoma fluviatilis|
|Plant Type||Herbaceous, perennial|
|Mature Size||2–3 in. tall, 1–2 ft. wide|
|Sun Exposure||Full, partial|
|Soil Type||Moist, well-draining|
|Soil pH||Acidic, neutral|
|Bloom Time||Spring, summer|
|Flower Color||Blue, purple|
|Hardiness Zones||6–8 (USDA)|
|Native Area||Australia, New Zealand|
Blue Star Creeper Care
Blue star creeper is an easy plant to grow, requiring little ongoing maintenance once established. It does best in a location that receives bright dappled shade but will also tolerate full sun, especially in cooler regions. Soil ideally should be kept consistently moist if possible. Drought does not kill the plants, but it may cause them to go dormant. Plant individual blue star creeper plants 12 to 18 inches apart, as the plants will quickly spread to create a thick coverage.
While blue star creepers are not invasive by definition, they are not native to the United States and can spread quickly, becoming troublesome in some situations. Keep this in mind when deciding where you’d like to plant blue star creeper. It can be easily contained with deep garden barriers or walls.
In its native habitat, blue star creeper is often found in moist areas with very bright dappled sunlight for the entire day. As a landscape plant, it can grow well in full direct sunlight in cooler regions, but in warmer regions it prefers some shade for part of the day. In shady conditions, the plant's growth may be more sparse, and flowers may be less plentiful.
Blue star creeper is not picky when it comes to soil. As long as it is planted in a moist, well-draining medium it will be happy. It grows best in a slightly acidic soil, but easily tolerates neutral and even slightly alkaline conditions.
Blue star creeper can be described as having medium water needs. During the summer, keep the soil moist with regular watering to support strong growth. A typical 1-inch-per-week watering schedule, preferably divided into two or more watering sessions, is ideal. Drought periods may see the plant go temporarily dormant, but don't let this go on for more than a few weeks.
Also avoid overwatering this plant if it is growing in dense, clay soil, as this can foster fungal diseases.
Temperature and Humidity
Blue star creeper is reliably cold-hardy in USDA zones 6 to 8. They are resilient plants that can withstand temperatures as low as minus 4 degrees Fahrenheit with snow cover. In these regions, it is often a semi-evergreen plant that goes dormant in the winter. It thrives as a reliably evergreen plant in regions with milder temperatures, though it does not like the intense prolonged heat of the deep South.
This plant does well in both dry and humid atmospheric conditions, provided soil moisture requirements are met.
Heavy fertilization is not required for blue star creeper. In fact, fertilizing blue star creeper too often can encourage aggressive growth which often becomes invasive. Fertilizing once at the beginning of the growing season with an all-purpose fertilizer will help to encourage strong new growth, but even this may not be needed if your soil is suitably rich.
Types of Blue Star Creeper
Isotoma fluviatilis is native to Australia and New Zealand and has several subspecies, differing mostly in leaf size and shape, though the differences can be almost impossible to spot without magnified inspection.
- Isotoma fluviatilis subsp. Fluviatilis is the most common variety of blue star creeper. Its tiny leaves are 1/4 to 1/2 inch long, and the flowers are about 1/4 inch across. There are no named cultivars offered for sale.
The other subspecies are rarely sold, and distinguishing them requires minute examination of the flower parts. These additional subspecies include Isotoma fluviatilis subsp. Australis, and Isotoma fluviatilis subsp. Borealis.
Pruning Blue Star Creeper
Shearing the foliage of a blue star creeper to about one inch tall in the late fall will help to keep the plant tidy throughout the winter and in the spring as new growth emerges. Other than this optional upkeep, blue star creeper is a low-maintenance perennial that does not require deadheading, flowering throughout the spring and summer continuously without assistance.
Propagating Blue Star Creeper
Blue star creeper is readily propagated by seed and by division. Blue star creeper spreads by rhizomes that extend both above-ground and below-ground, which means that plants can be easily divided and transplanted. Here's how to do it:
- Using a sharp shovel or trowel, carefully dig around the rhizomes and root ball, preserving as many roots as possible.
- Gently separate plants from one another by tugging the roots apart with your fingers.
- Immediately plant the pieces in new locations. If the goal is a groundcover blanket, space them 12 to 18 inches apart; they will fill in within a single growing season.
Division is generally not necessary for the health of blue star creeper, but overgrown colonies are sometimes rejuvenated if you dig up the entire colony and replant with added space between plants.
Growing Blue Star Creeper From Seed
Blue star creeper seeds can be harvested from the dried seed pods left behind when flowers fade, or purchased from online retailers. Sow the tiny seeds on moistened seed starter mix and cover the container with plastic wrap. Keep the container in a location where it receives partial sunlight, and keep the soil consistently moist, but not wet, until the seeds sprout. Blue star creeper seeds take anywhere from 7 to 15 days to sprout, so be patient. Remove the plastic wrap when seeds have sprouted.
Potting and Repotting Blue Star Creeper
Although container culture is not common, blue star creeper can certainly be grown in pots, either alone to provide spots of texture and color, or as spiller plants around the edges of mixed containers. Use a standard potting mix and a well-draining pot of any material you choose. If growing them as perennials, plan to repot every year or two, moving up one pot size each time. Or, you can grow potted blue star creepers as annuals, discarding them at the end of the growing season.
Within its recognized hardiness range, blue star creeper requires no winter cold protection. In regions with winter snow cover, a close shearing with a lawn mower followed by a light raking to remove debris is good practice before winter sets in.
Common Pests & Plant Diseases
Blue star creeper has virtually no insect pests to be concerned about, but fungal diseases can be an issue if the plant is growing in soil with poor drainage, or in low-lying areas where water gathers. Badly affected plants should be removed to prevent the spread of disease. Amend the soil to improve drainage before replanting.
How to Get Blue Star Creeper to Bloom
While the growing season varies, blue star creeper usually blooms from spring into fall, with peak flowering occurring in early summer. If the plants fail to bloom, it may be because they are not getting enough sunlight or are being overfed. A single fertilizer application in early spring is all that is necessary, but if the soil is already rich, even a single feeding may stimulate green growth while reducing flower production.
Common Problems With Blue Star Creeper
There are only a few common cultural complaints about blue star creeper:
If brown, apparently dead patches appear in your ground cover, it is likely because there are areas are collecting water and causing fungal disease that is killing plants. Remove affected plants and add soil amendments to improve drainage before replanting.
Plants Spread Aggressively
Blue star creeper is not officially considered an invasive species, but it can, and often does, spread beyond its borders. It can take over a garden if you are not careful to chop away runners and dig up plants that sprout up where you don't want them. Installing deep edgings (at least 1 foot deep), will help keep this plant from spreading into areas where it is not welcome.
Plants Go Brown in Winter
In the northern part of its hardiness range, blue star creeper is best described as semi-evergreen. It will usually go dormant and turn brown during the winter, returning to active green growth in spring—much the way turf-grass lawns perform in these regions. In regions with milder winters, the plant is usually evergreen, though it doesn't flower in the winter.
How is this plant best used in the landscape?
Blue star creeper is an increasingly popular alternative to turfgrass for covering sunny areas with a ground cover that needs little maintenance. It is also a good choice for blanketing areas beneath shrubs, or for covering areas where spring bulbs are grown. It makes a good filler between pavers in stepping-stone pathways. It can also make a good edging plant along streams or ponds.
Are there similar ground covers that work well in colder climates?
In zones 4 to 9, periwinkle (Vinca minor) can be used in a similar manner, as a ground cover for blanketing sunny areas. Vinca minor has glossy deep green leaves and deep indigo flowers, and it spreads through runners. But like blue star creeper, Vinca minor needs to be supervised to prevent unwanted spread.