Cast Iron Plant is grown for its foliage and the structure it brings to a planting. It's hardy across USDA zones 7 through 11, shrugs off deer, shrugs off dry spells, and grows just as well in a container as in the ground.
Cast Iron Plant — the short answer
Cast Iron Plant: grown in zones 7–11, shade, pH 5.5–7.
- USDA zones
- 7–11
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- Soil pH
- 5.5–7
- Growable Ground Plant Database
- Sun
- Shade
- Growable Ground Plant Database
- Frost-kill temp (growing season)
- 0°F
- Growable Ground Plant Database
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — each tile names its own row's source, because per-field provenance varies.
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What Cast Iron Plant is
Cast Iron Plant grows as a perennial and reaches around two feet at maturity. It blooms purple in spring. It's also deer-resistant and well suited to containers.
How to grow Cast Iron Plant
Cast Iron Plant grows in USDA zones 7 through 11. Cast Iron Plant does best in shade — at least 2 hours of direct sun a day — and soil from pH 5.5 to 7, on well-drained ground. It needs a growing season of at least 120 frost-free days, which is why climate matters as much as soil.
USDA Zones
7-11
USDA PHZM 2023
Soil pH
5.5 - 7
Growable Ground Plant Database
Sun
Shade
Growable Ground plant catalog
Drainage
well (dry spells)
Growable Ground plant catalog
Frost Kill Temperature
0°F
Where cold starts killing growing tissue. Not a winter-survival floor — a dormant perennial takes far colder, which its hardiness zone answers.
Growable Ground Plant Database
Mature Height
2 ft
Growable Ground plant catalog
Frost-Free Days
120+
The frost-free stretch it needs start to finish — short-season areas may need an indoor head start.
Growable Ground plant catalog
Start the season right
Plant cast iron plant in shade with at least 2 hours of direct sun, once the soil has warmed and frost risk has passed.
Match the soil
Cast Iron Plant prefers pH 5.5 to 7 (Growable Ground Plant Database). A quick soil test from your local Extension lab tells you whether to add lime or sulfur to land in band.
Water steadily
Keep the root zone evenly moist through establishment. A 2–3 inch mulch layer holds moisture without waterlogging.
Keep it in good form
Prune cast iron plant to shape as it grows; the reward is its foliage and structure, not a harvest, so steady upkeep is the whole job.
Where Cast Iron Plant thrives
Cast Iron Plant is hardy across USDA zones 7 through 11. Zone is only the starting point, though: the soil pH, drainage, and frost dates on your specific land decide how well it actually does.
A USDA zone is a 10°F band of average annual extreme winter minimum, so zones 7–11 spans average winter lows from 0°F to 50°F (USDA PHZM 2023). Across the 50 states and DC, that band covers 7 outright and splits 34 more down the middle — and which side of that line your land sits on changes the answer.
Zones 7–11·Where Cast Iron Plant growsOpen map →
This map is derived from the USDA ARS / PRISM Plant Hardiness Zone Map (2023) and is not the official USDA Plant Hardiness Zone Map.
Where Cast Iron Plant stands, state by state
Cast Iron Plant is rated for zones 7–11 — a cold floor USDA puts at 0 to 10°F. Across the 50 states and DC, 7 sit fully inside that band, the line runs through 34 more, and 10 sit outside it — and inside every split state, the same line runs on at county grain.
Fully inside zones 7–11
7 states
- Alabama · zones 7b-9b
- Delaware · zones 7a-8a
- District of Columbia · zones 7b-8a
3 of 7 shown
The line runs through
34 states
3 of 34 shown
Cast Iron Plant’s band covers part of each of these states — which side of the line your county sits on changes the answer, and each state page draws it.
Outside zones 7–11
10 states
- Minnesota · zones 3a-5a
- Montana · zones 3a-6b
- New Hampshire · zones 3b-6b
3 of 10 shown
Winter cold is the limit here — the same plant often works in a container that comes under cover. Each link is that state’s own growing hub.
State zone extents: USDA Plant Hardiness Zone Map (PHZM) 2023. A zone is a 10°F band of average annual extreme minimum temperature, so a state that splits the band contains the boundary — its own page draws the county line, and a parcel report resolves which side your land sits on.
What grows around Cast Iron Plant
Growing guides for cast iron plant
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Good to know
Good news for pet owners — cast iron plant isn't known to be toxic to dogs or cats. (Source: ASPCA.)
Cast Iron Plant isn't classified as a notable pollinator plant in our data — pair it with high-value bloomers nearby to feed bees.
Your land is one point inside Cast Iron Plant's range
This page resolves to the species. Your state page draws the county line, and a report reads the parcel — the soil pH, drainage, sun, and frost dates on your exact ground, which no species average can see.
See if Cast Iron Plant will thrive on your land
Zone averages are a start. Your exact soil pH, drainage, sun exposure, and frost dates shape whether cast iron plant actually takes — we score it against the real conditions at your address.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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How we know this about Cast Iron Plant
The figures above are cited per row, not per site: the pH band names this plant’s own source column, the three temperature figures each carry their own, and days-to-maturity cites the publication that actually lists it. All of it comes from the Growable Ground Plant Database — a compilation over FAO ECOCROP, USDA PLANTS, and university Extension sources, published openly with per-field provenance.
Grounded inUSDA PLANTS Database•USDA PHZM•ASPCA
Frequently asked questions
Can I grow Cast Iron Plant in my zone?
Cast Iron Plant grows in USDA hardiness zones 7 through 11 (USDA PHZM 2023). Zone is one factor — soil pH, drainage, and frost dates on your specific parcel also shape whether it takes.
When should you plant Cast Iron Plant?
Most growers plant cast iron plant after the last spring frost, once the soil has warmed, leaving enough of the season for its 120-day frost-free need. Your local frost dates set the exact window — a Growable Ground report reads them for your address.
How much sun does Cast Iron Plant need?
Cast Iron Plant is shade-tolerant — it gets by on as little as 2 hours of direct sun, so it earns a place most vegetables can't use. A north-facing strip or the ground under a leafy canopy is right where it belongs. A Growable Ground report shows which corners of your land stay shaded through the day, turning those dim spots into planting spots.
What soil does Cast Iron Plant need?
Cast Iron Plant prefers soil pH 5.5 to 7, on well-drained ground (Growable Ground Plant Database). Your report scores your parcel's actual soil against that using USDA SSURGO data.
Does Cast Iron Plant attract pollinators?
Cast Iron Plant isn't classified as a notable pollinator plant in our data. Pairing it with high-value bloomers nearby keeps bees and butterflies fed.
Is Cast Iron Plant safe for pets?
Cast Iron Plant is not known to be toxic to dogs or cats based on available data. Always supervise pets around new plantings. (Source: ASPCA.)
Keep exploring Cast Iron Plant
Cast Iron Plant state by state
Every state cast iron plant's zone reaches — 13 link straight to that state's cast iron plant growing page; the rest open the state's full growing guide.