Illustration
Red Sentinel
Astilbe × arendsii 'Red Sentinel'
Red Sentinel blooms from June through July.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Red Sentinel
Plant it in part shade. It prefers high water. It is hardy in USDA zones 4–8. Expect it to reach about 24 in tall and 20 in wide at maturity, in roughly 2 years (a house reading).
No toxicity note is on file for Red Sentinel. That is not a clearance: check its safety for people and pets before planting.
What was checked
Mature height and spread, hardiness zones, sun, water, bloom months and color and the trait tags were checked against named botanical sources for this plant, with what the sources could not settle written down; years to mature size rests on a recorded house rule where no publisher states one, and is marked so; its common name and alternate names have not been checked yet. 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 Red Sentinel
Plant Red Sentinel 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 6, the middle of its hardy zones 4 to 8, spring means March to May and fall means August or September. Once settled, it blooms from June to July.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 6, the middle of this plant's hardy range, start with zone 6 in March. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Red Sentinel get?
24 intall5 ft 7 inan adult20 inwideSee Red Sentinel 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 Red Sentinel
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Red Sentinel about 20 in apart, center to center, so each plant has room to reach its full width.
Add Red Sentinel 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
Red Sentinel's height, spread, hardiness zones, sun, water, bloom months and color, trait tags, soil, diseases, pests and toxicity were checked against 9 published sources on August 24, 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 GardenPlant Finderheight, spread, hardiness zones, sun, water, bloom months and color, trait tags, soil, diseases and pests
- University of Illinois ExtensionHort Answersheight, hardiness zones, sun, water, bloom months and color, soil, diseases and pests
- plants.gertens.comNetPS Plant Finder (served at plants.gertens.com)height, spread, hardiness zones, sun and bloom months and color
- NC State ExtensionPlant Toolboxhardiness zones, water, soil, diseases and pests
- Pleasant Run Nurseryheight, hardiness zones, sun and bloom months and color
- Walters Gardensheight, spread, water and bloom months and color
- Penn State Extensiondiseases and pests
- Plants For A Futuretoxicity
- uvm.eduUniversity of Vermont Extension, Department of Plant and Soil Sciencetoxicity
How the checking works, and what each standard covers, is on the verified plants page.
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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.