The Star of Bethlehem flower, scientifically known as Ornithogalum umbellatum, is an aggressive perennial weed that colonizes lawns and garden beds. Originating in Europe and North Africa, this plant has become a widespread invasive species in many regions. Its white, star-shaped flowers appear briefly in spring, but its foliage quickly forms dense, grass-like clumps that outcompete desirable turf and ornamentals. Eradicating this invasive bulbous plant requires a persistent, multi-year strategy to achieve successful control.
Understanding Why This Weed Is Difficult to Eradicate
The primary challenge in controlling Ornithogalum umbellatum stems from its unique subterranean reproductive structure. Unlike many weeds that spread primarily by seed, the Star of Bethlehem relies on the rapid production of numerous small, underground bulblets. These miniature bulbs form dense colonies just beneath the soil surface, and a single parent plant can produce dozens of these offsets in one season, making its spread exponential and localized.
The small size and high density of these bulblets mean that any mechanical disturbance, such as tilling or incomplete digging, often makes the infestation significantly worse. When the soil is turned, the bulblets are scattered throughout the area, allowing each one to establish a new, separate plant. Furthermore, the plant’s narrow, fleshy leaves are coated in a waxy cuticle, which acts as a barrier against many common contact herbicides. This protective layer prevents chemicals from penetrating the leaf surface and reaching the plant’s vascular system effectively.
The plant completes its vegetative cycle quickly in the spring. Its foliage emerges early, often before other plants, and then dies back and goes dormant by mid-summer. This short period of active growth limits the window during which herbicides can be successfully applied and transported down to the underground bulbs, making it undetectable and inaccessible for control methods during the hottest months.
Manual and Cultural Control Methods
For smaller, isolated patches, manual removal is a viable option, provided it is executed with extreme care. The goal is to remove the entire bulb cluster and all surrounding bulblets without leaving any behind to resprout. It is best to dig when the soil is slightly moist, using a small trowel to remove a generous amount of soil around the visible foliage cluster. All removed soil must be inspected meticulously to ensure every tiny bulblet is collected, as leaving even a few can restart the infestation.
Soil Solarization and Smothering
A more intensive, non-chemical approach for larger areas is soil solarization or smothering. These methods kill the bulbs by depriving them of light and subjecting them to extreme heat. To solarize, clear plastic sheeting is laid over the infested area during the hottest months, trapping solar radiation to raise the soil temperature high enough to cook the bulbs. Alternatively, smothering uses thick, opaque materials like black plastic or old carpet, which starves the bulbs of light over an extended period. These coverings must remain in place for at least one full growing season, and ideally two, to ensure that deep-lying bulbs are exhausted of their stored energy.
Cultural Practices
Cultural practices focus on weakening the plant over time by preventing photosynthesis and replenishing its bulb energy reserves. In turf areas, persistent, close mowing immediately after the leaves emerge prevents the plant from gathering enough light to sustain the bulb. Repeatedly cutting the foliage to the ground as soon as it appears will eventually deplete the energy stored in the underground bulb. This strategy requires a commitment to consistency until the bulb is completely starved.
Herbicide Application and Timing
When manual control is impractical due to the size of the infestation, systemic post-emergent herbicides offer the most effective chemical solution. These products are designed to be absorbed by the foliage and translocated through the plant’s vascular system down to the root structure, targeting the underground bulblets. Selective broadleaf weed killers are commonly used, including those containing:
- Dicamba
- 2,4-D
- Triclopyr
- Carfentrazone
- Sulfentrazone
The critical factor for success is precise timing, which must align with the plant’s active growth phase. The best time to apply systemic chemicals is in late fall or very early spring, immediately after the leaves emerge but before the plant flowers and enters summer dormancy. Applying the herbicide during this narrow window ensures the plant is actively moving nutrients down to the bulb, carrying the chemical along. Once the plant flowers and the foliage dies back, the flow of nutrients stops, rendering the application ineffective.
Because of the plant’s waxy leaves, adding a non-ionic surfactant or liquid dish soap to the mixture is highly recommended. This additive breaks the surface tension and allows the chemical solution to penetrate the protective cuticle for better absorption. Multiple applications are almost always necessary, typically repeating the treatment two to three times annually for several consecutive years.
Monitoring and Preventing Re-Infestation
Achieving complete eradication requires continued monitoring for several seasons after initial control efforts. Dormant bulblets can remain viable in the soil for an extended period, meaning new shoots may appear in subsequent spring seasons. Regular inspection of the treated area, particularly in early spring, is necessary to catch emerging foliage before it replenishes the bulblets’ energy stores. Any new tufts of leaves should be immediately treated with careful digging or a targeted spot application of a systemic herbicide.
Long-term prevention involves establishing healthy, dense plant cover that limits the Star of Bethlehem’s ability to compete for resources. Planting thick turfgrass or a desirable ground cover creates a competitive environment that denies the weed the light and space it needs. Maintaining a vigorous lawn through proper fertilization, watering, and mowing will help crowd out remaining or new seedlings. Since the plant favors moist, fertile soil, improving soil drainage in chronically wet areas can also help make the environment less conducive to its growth.