Illustration
Lilac Lobelia
Lobelia erinus
Lilac Lobelia blooms from May through September.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Lilac Lobelia
Plant it in part sun. It prefers moderate water. Expect it to reach about 8 in tall and 10 in wide at maturity, in roughly 1 year (a house reading).
Is Lilac Lobelia toxic to dogs or cats?
- Listed as toxic to dogs and cats by South Dakota State University Extension.
- Listed as poisonous to people by NC State Extension.
Lists differ and none is complete. If a pet eats a plant and seems unwell, call a veterinarian or a pet poison helpline.
What was checked
Nine facts were checked against named botanical sources, each recorded beside the sources that carried it: mature height and spread, hardiness zones, sun, water, bloom months and color, the trait tags, and years to mature size, which rests on a recorded house rule where no publisher states one and is marked so. Soil, diseases, pests, toxicity and the plant's own names have not yet been read for this plant, and its trait tags are the ones a feature uses rather than every word a page prints. Each fact above carries its own mark. The planting, spacing and size sections are derived from these checked facts by a fixed rule, not checked separately, and the plant type is the library's own classification.
When to plant Lilac Lobelia
Wait until all danger of frost has passed, then plant out Lilac Lobelia into warm soil; in most zones that means late spring. Planted then, it flowers from May to September.
Month-by-month timing for your zone is on the planting calendar. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Lilac Lobelia get?
8 intall5 ft 7 inan adult10 inwideSee Lilac Lobelia in a garden plan: the planner shows it in 3D beside everything else you add, growing toward this size over the years.
How far apart to plant Lilac Lobelia
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Lilac Lobelia about 10 in apart, center to center, so each plant has room to reach its full width.
Add Lilac Lobelia to a garden plan and the planner draws it at its full width, so you see the spacing before you buy.
Where these facts come from
Lilac Lobelia's height, spread, hardiness zones, sun, water, bloom months and color and trait tags were checked against 5 published sources on October 27, 2026. Each one is linked below with every fact it carried, which can include a fact this page still marks as not yet checked, because a source carrying a value is not the same as the value being held to the standard. Facts not in that list, and the planting, spacing and size sections, are not covered by these sources.
- Missouri Botanical Gardenheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- NC State Extensionheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- RHSRoyal Horticultural Societysun, water and bloom months and color
- University of Illinois Extensionheight, sun and bloom months and color
- benary.comBenarybloom months and color and trait tags
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Lilac Lobelia
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
Toxic to dogs, cats and horses, and to people if eaten in quantity. All parts hold lobeline, a nicotine-like alkaloid; keep pets and children from grazing it. per ASPCA and NC State
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Design a garden with this
Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.