Broadstem Onion Plant Care
Allium platycaule S.Watson
Updated · Sources · How we source care data
Allium platycaule is a species of wild onion known as broadstemmed onion or flat-stem onion. It is native to northeastern California, south-central Oregon and northwestern Nevada.
Every 7–14 days
Full sun to partial shade
50–75°F
40–60%
At a glance
How do you care for Broadstem Onion?
Water Broadstem Onion every 7–14 days, letting the top layer of soil dry out between waterings, and give it full sun to partial shade. It prefers temperatures of 50–75°F (10–24°C) and 40–60% humidity. Fertilize it every 6 months during the growing season. It is reported as toxic to pets, so keep it out of reach of pets.
Where Is the Broadstem Onion Native To?
What Is the Broadstem Onion?
Broadstem Onion (Allium platycaule) belongs to the Amaryllidaceae family within the Allium genus. Broadstem Onion is native to northeastern California, south-central Oregon and northwestern Nevada. Broadstem Onion is also known as Flatstem Onion.
Broadstem Onion displays an upright, clumping perennial growth habit, reaching up to 2 ft tall with a spread of approximately 0.5 ft. Broadstem Onion produces spherical clusters of small purple, white, or pink flowers.
Leaf size: approximately 12 inches.
How Often Should You Water a Broadstem Onion?
Allium platycaule requires watering every 7–14 days. Allow the top layer of soil to dry between waterings to prevent root rot. Reduce watering frequency during winter when growth slows.
Watering Frequency
Every 7–14 days
Let soil partially dry between waterings
What Light Does the Broadstem Onion Need?
Broadstem Onion thrives in full sun to partial shade.
Light Requirement
Full sun to partial shade
What Temperature and Humidity Does the Broadstem Onion Prefer?
Allium platycaule grows best at temperatures of 50–75°F. Broadstem Onion prefers humidity levels of 40–60%.
Temperature
50–75°F
Humidity
40–60%
What Soil Mix Works Best for a Broadstem Onion?
Well-draining sandy loam with added compost for nutrients. Good drainage is essential for Broadstem Onion to prevent waterlogging, which leads to root rot and fungal issues.
How Often Should You Fertilize a Broadstem Onion?
Feed Broadstem Onion every 6 months during the growing season (spring and summer) with a balanced fertilizer diluted to the strength on the label.
Pause feeding in autumn and winter, when growth slows, and never fertilize dry soil — water first.
Fertilizing
Every 6 months
During the growing season
The PlantoScan app can remind you when to water and when to fertilize each plant.
How Do You Repot a Broadstem Onion?
Divide and repot every 3-4 years in early spring. Choose a pot one size larger than the current container, and ensure it has drainage holes to allow excess water to escape.
How Do You Propagate a Broadstem Onion?
Broadstem Onion can be propagated through division of bulbs, offsets, seeds. Similar propagation techniques also apply to onion plant care, which shares the same genus.
Is the Broadstem Onion Toxic to Pets and Children?
Toxic (caution)
Reported as toxic in our plant data. Not verified by the ASPCA.
Toxic to dogs, cats, and horses if ingested
This is a general caution, not veterinary or medical advice. If your pet ate a plant, contact your vet or animal poison control.
See all plants toxic to cats and plants toxic to dogs.
What Pests and Diseases Affect the Broadstem Onion?
Broadstem Onion is susceptible to onion thrips, onion maggots. Inspect the foliage regularly, especially along leaf undersides and stems. Treat infestations promptly with insecticidal soap or neem oil to prevent spread.
Yellow leaves, brown tips or drooping? See common plant problems and how to fix them.
What USDA Hardiness Zone Does the Broadstem Onion Need?
Broadstem Onion grows outdoors in USDA Zone 12a. It survives winters down to planting zone 12a. Broadstem Onion is native to northeastern California, south-central Oregon and northwestern Nevada. In cooler regions, grow Broadstem Onion as a houseplant or bring it indoors before the first frost.
Hardiness Zone
Zone 12a
Keep exploring plants
Broadstem Onion is one of many species covered in the complete plant care and identification guide, which groups plants by genus, attribute, and popularity.
It belongs to the Allium genus — compare its care with other Allium species on PlantoScan.
Allium is part of the Amaryllidaceae plant family — browse all Amaryllidaceae genera and species.
Broadstem Onion thrives in bright light and direct sun — see other bright-light plants.
More Allium Species
Other Allium species in PlantoScan's care catalogue share similar watering, light, and soil preferences:
Sources
- Scientific name & taxonomy: Allium platycaule S.Watson, family Amaryllidaceae (first published in Proc. Amer. Acad. Arts 14: 234 (1879)) — World Flora Online record, IPNI name record.
- Pet toxicity: Broadstem Onion is reported as toxic to pets in our plant data (not verified by the ASPCA), so treat it with caution. Checked against the ASPCA plant list; any other toxicity note on this page comes from PlantoScan's plant database.
- Hardiness zone: USDA Zone 12a, calculated from the plant's minimum temperature.
- Care values(watering, light, temperature, humidity, soil, fertilizing): PlantoScan's plant database, filtered by automatic plausibility checks — values that fail them are hidden. How we source and check plant data.
Spotted a mistake? Email info@upvision.media with the page link — we check and correct reported errors.
Identify Plants Like the
Broadstem Onion Instantly
Scan any plant with your phone camera and get instant ID, care tips, water and fertilizer reminders, and health checks — all in one app.
Free
to download
iOS & Android
platforms
Light & dark
mode
100,000+
species