Illustration
Monkshood
Aconitum
Also comes in white.
Monkshood blooms from August through September.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Monkshood
Plant it in part sun. It prefers moderate water. It is hardy in USDA zones 3–7. Expect it to reach about 4 ft tall and 1.5 ft wide at maturity, in roughly 3 years (not yet checked).
What was checked
Mature height and spread, hardiness zones, sun and the trait tags were checked against named botanical sources for this plant. The bloom months and water need on this page were not, and each fact above says which. 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 Monkshood
Plant Monkshood in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. In zone 5, the middle of its hardy zones 3 to 7, spring means April to June and fall means August or September. Once settled, it blooms from August to September.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 5, the middle of this plant's hardy range, start with zone 5 in April. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Monkshood get?
4 fttall5 ft 7 inan adult1.5 ftwideSee Monkshood 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 Monkshood
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Monkshood about 1.5 ft apart, center to center, so each plant has room to reach its full width.
Add Monkshood 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
Monkshood's height, spread, hardiness zones, sun and trait tags were checked against 14 published sources on August 1, 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.
- NC State ExtensionPlant Toolboxheight, spread, hardiness zones, sun, years to mature size and trait tags
- Walters Gardensheight, spread, hardiness zones, sun, years to mature size and trait tags
- Missouri Botanical GardenPlant Finderheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenPlant Finderheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenPlant Finderheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenPlant Finderheight, spread, hardiness zones, sun and trait tags
- fieldstonegardens.comFieldstone Gardensheight, spread, hardiness zones and sun
- horsfordnursery.comHorsford Gardens and Nurseryheight, spread, hardiness zones and sun
- NC State ExtensionPlant Toolboxhardiness zones, sun, years to mature size and trait tags
- plants.gertens.comGertens (NetPS Plant Finder)height, spread, hardiness zones and trait tags
- RHSheight, spread, sun and years to mature size
- University of Illinois Extensionheight, hardiness zones, sun and trait tags
- Chicago Botanic GardenPlant Finderhardiness zones, sun and trait tags
- Lady Bird Johnson Wildflower Centersun
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Monkshood
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note. A note reports what its source says; where that differs from a fact above, the fact above is this entry's stored value, and its mark says whether it has been checked.
Safety
One of the most poisonous garden plants. Every part holds aconitine, with roots and seeds worst; toxic to people, dogs and cats, and can be fatal if eaten. per NC State
Worth knowing
The same aconitine that makes it dangerous is why deer and rabbits leave it untouched: browsers will not eat it. per NC State
Divide or leave it?
NC State lists division as a way to propagate it, but Illinois calls it hard to move. It resents disturbance, so leave it undisturbed. per NC State and Illinois
Always wear gloves
The toxins soak through skin, worse through cuts, so NC State says wear gloves. Take extra care with the roots and seeds, the most toxic parts. per NC State and Forensic Sciences Research
Keep it from vegetables
NC State warns against planting it near the vegetable garden: the fleshy roots can be mistaken for an edible root like Jerusalem artichoke or horseradish, a documented fatal mistake. per NC State
Dislikes heat
A cool-climate plant that struggles in hot summers. In the South, give it afternoon or dappled shade and keep the roots cool and moist, or it may not last. per Arkansas
Wolfsbane, queen of poisons
Also called wolfsbane and 'queen of poisons' for its toxicity. It was once used to poison wolves and to tip arrows and harpoons. per NC State
What pairs well with Monkshood
Good companions share its growing conditions and add something it lacks: an earlier or later bloom, a lower carpet in front, or structure through winter.
White Clover
Takes full sun to part sun and moderate water; blooms in late spring, before this one opens; low at 4 in, to carpet the ground beneath; both offer pollinator forage, in different months.
Creeping Sedum
Takes full sun to part sun and low to moderate water; opens in early summer and overlaps into this one's season; low at 4 in, to carpet the ground beneath; evergreen, so the bed keeps its shape through winter.
Sea Thrift
Takes full sun to part sun and low to moderate water; blooms in mid spring, before this one opens; lower at 8 in, for the front of the border; evergreen, so the bed keeps its shape through winter.
Thyme
Takes full sun to part sun and low to moderate water; blooms in late spring, before this one opens; low at 6 in, to carpet the ground beneath; both offer pollinator forage, in different months.
Snowdrop
Takes part sun to part shade and moderate water; blooms in late winter, extending the bed's season; low at 5 in, to carpet the ground beneath; both offer pollinator forage, in different months.
Rhododendron
Takes part sun to part shade and moderate water; blooms in late spring, before this one opens; both offer pollinator forage, in different months; evergreen, so the bed keeps its shape through winter.
Japanese Stewartia
Shares part sun and moderate water; blooms in early summer, before this one opens; both offer pollinator forage, in different months; taller at 16 ft, for the layer behind it.
Sweet Alyssum
Takes full sun to part sun and moderate water; overlaps, then carries the display into mid fall; low at 5 in, to carpet the ground beneath; both offer pollinator forage.
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Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.