Ironwood is grown for its foliage and the structure it brings to a planting. It's hardy across USDA zones 10 through 13 and shrugs off dry spells. A nitrogen-fixer, it draws nitrogen from the air and feeds it back to the soil — turn it under or leave the roots in place, and the next planting inherits a richer bed.
Ironwood — the short answer
Ironwood: grown in zones 10–13, full sun, pH 6.8–8.6.
- USDA zones
- 10–13
- 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
- 6.8–8.6
- USDA PLANTS
- Sun
- Full Sun
- 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.
Score Ironwood on your exact land.
Zone averages can't see the slope, soil, frost, and sun that decide whether ironwood actually takes — and those shift from one yard to the next. Enter your address and we'll score ironwood against your land's real conditions.
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What Ironwood is
Ironwood grows as a perennial. It blooms purple in early spring.
How to grow Ironwood
Ironwood grows in USDA zones 10 through 13. Ironwood does best in full sun — at least 6 hours of direct sun a day — and soil from pH 6.8 to 8.6. It needs a growing season of at least 365 frost-free days, which is why climate matters as much as soil.
USDA Zones
10-13
USDA PHZM 2023
Soil pH
6.8 - 8.6
USDA PLANTS
Sun
Full Sun
Growable Ground plant catalog
Drainage
Data pending
Growable Ground plant catalog
Cold Hardiness
22°F
The coldest temperature this plant is documented to survive.
USDA PLANTS
Frost-Free Days
365+
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 ironwood in full sun with at least 6 hours of direct sun.
Match the soil
Ironwood prefers pH 6.8 to 8.6 (USDA PLANTS). A quick soil test from your local Extension lab tells you whether to add lime or sulfur to land in band. It fixes its own nitrogen, so skip the high-nitrogen feed and instead dust the seed with a matching rhizobium inoculant at sowing.
Water steadily
Keep the root zone evenly moist through establishment. Match watering to the plant's drainage preference and your local rainfall.
Keep it in good form
Prune ironwood to shape as it grows; the reward is its foliage and structure, not a harvest, so steady upkeep is the whole job.
Where Ironwood thrives
Ironwood is hardy across USDA zones 10 through 13. 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 10–13 spans average winter lows from 30°F to 70°F (USDA PHZM 2023). Across the 50 states and DC, that band covers none outright but splits 8 down the middle — and which side of that line your land sits on changes the answer.
Zones 10–13·Where Ironwood growsOpen map →
Continental US shown — Alaska and US Pacific territories sit outside the federal map's polygon dataset.
Where Ironwood stands, state by state
Ironwood is rated for zones 10–13 — a cold floor USDA puts at 30 to 40°F. Across the 50 states and DC, 0 sit fully inside that band, the line runs through 8 more, and 43 sit outside it — and inside every split state, the same line runs on at county grain.
The line runs through
8 states
- California · zones 4b-11a
- Nevada · zones 4a-10a
- Arizona · zones 5b-10b
3 of 8 shown
Ironwood’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.
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 Ironwood
Growing guides for ironwood
In rotation planning, ironwood counts as a Legume — beds recover best when legume crops don’t follow each other in the same spot year over year. (Growable Ground derivation — crop-rotation group from botanical family)
Good to know
Good news for pet owners — ironwood isn't known to be toxic to dogs or cats. (Source: ASPCA.)
Your land is one point inside Ironwood'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 Ironwood will thrive on your land
Zone averages are a start. Your exact soil pH, drainage, sun exposure, and frost dates shape whether ironwood 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 Ironwood
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 Ironwood in my zone?
Ironwood grows in USDA hardiness zones 10 through 13 (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 Ironwood?
Time ironwood to your own season rather than the calendar, leaving enough of the season for its 365-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 Ironwood need?
Ironwood needs full sun — a spot that catches at least 6 hours of direct summer sun a day. In more shade it still grows, but usually gives a smaller, later crop. The catch is that a yard rarely gets even light everywhere — a fence, the house, or one tall tree can quietly take those hours. A Growable Ground report reads the real sun-hours across your land, canopy and buildings included, so you can pick the brightest bed before you plant.
What soil does Ironwood need?
Ironwood prefers soil pH 6.8 to 8.6 (USDA PLANTS). Your report scores your parcel's actual soil against that using USDA SSURGO data.
Is Ironwood safe for pets?
Ironwood is not known to be toxic to dogs or cats based on available data. Always supervise pets around new plantings. (Source: ASPCA.)