Yes — Strong Match
torenia is grown as an annual, so season length decides it here, not a winter zone — and Utah's typical season runs ~175 frost-free days against the ~80 torenia needs.
Sow by about Aug 14
Torenia is grown as an annual, so what decides it here is season length, not a winter zone. It needs about 80 frost-free days and a typical Utah season runs ~175 frost-free days, leaving 95 days of slack. That is room to sow as late as about Aug 14 and still finish before the usual first freeze (Oct 18).
Want more weeks at either end of that window? How to buy the weeks →
80 frost-free days required against Utah’s ~175-day season. NOAA Regional Climate Centers ACIS 1991-2020 (28°F killing freeze), state median across counties, via stateClimateData.ts.
Your yard isn't the whole zone.
Torenia is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical Utah site runs ~175 frost-free days, but that is a state median, not your yard: slope, trees, and low spots move the last-frost date across a single parcel. Enter your address and we'll score torenia against your land's actual frost dates, sun, and soil.
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Zone Comparison
Torenia Needs
- USDA Zones: Data pending
- Frost-Free Days: 80+
- Sun: Part Sun
- Mature size: 1 ft tall
- Picking window: ~90 days of harvest
- Drought tolerance: Low
Utah Has
- USDA Zones: 4a-9a
- Last Hard Freeze (28°F): Apr 12 - May 6
- First Hard Freeze (28°F): Oct 8 - Oct 27
- Annual Rainfall: 5-20 inches
- Common Soils: Sandy loam, Alkaline clay, Desert sand
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Torenia in Utah
The frost window
Across Utah, the last spring hard freeze (28°F) clears between Apr 12 and May 6, and the first fall hard freeze lands between Oct 8 and Oct 27 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 155-day window you can count on — up to 198 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
When to start the seed
Those dates are when torenia goes out, not when it starts. It is sown under cover about 10 weeks ahead, so counting back from Utah's late-side last freeze of May 6 is what fixes your sowing date — and a yard that clears frost earlier than the state's late date starts earlier still.
Days to maturity vs. the window
At 65 days to maturity (USDA PLANTS Database), counting from the last hard freeze it ripens with 90 days to spare even in Utah's tightest freeze scenario — room for a later start or a second sowing.
Timing tuned to sub-state frost dates — Summit County, not the statewide average.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
Frost-free days
Torenia wants 80+ frost-free days; a typical Utah site sees ~175 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Torenia needs ~1300 GDD (base 50°F) to ripen. The state median runs ~2690 GDD (from PRISM 1991-2020 climate normals), so Utah's typical season clears that easily.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Torenia likes near-neutral soil (pH 5.5-7). That's the common-ground band across Utah's sandy loam and alkaline clay — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 6 and 6.5 — worth knowing before you decide whether a Utah soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Utah site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Utah's soils run mostly loam, but SSURGO maps the series, texture, and drainage under your exact parcel. What matters for torenia is the horizon its roots actually work, not the surface. That map unit, not the state average, decides how torenia performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Utah soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Torenia in Utah — Quick Answer
- Verdict: Yes — Strong Match
- Plant Zones: Data pending (USDA PLANTS Database)
- State Zones: 4a-9a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Apr 12 - May 6 to Oct 8 - Oct 27 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 65 days
What Else to Consider for Torenia in Utah
Zone compatibility tells you about winter cold survival — but Utah growers also need to think about:
Very low rainfall — irrigation essential
Alkaline soils (pH 7.5-8.5) limit many species
High altitude frost risk in mountain valleys
Growing torenia here specifically
Utah's soils run mostly loam (Mollisols), and whether that suits torenia's pH 5.5–7.0 preference comes down to your exact parcel, not the statewide picture.
Pull your parcel's SSURGO map unit, test pH, and amend toward torenia's 5.5–7.0 target before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Utah grower, not just torenia — is covered on the Utah growing guide.
Timing shifts within Utah
Utah isn't one climate. In Summit County, the last hard freeze (28°F) holds until about Jun 10 — roughly 45 days later than the recorded state median — so plant torenia to your county's window, not the statewide date.
Torenia needs about 80 days of frost-free season to complete its cycle. Even Summit County — Utah’s shortest season at 98 frost-free days — clears that by 18 days, so season length isn’t the constraint anywhere in Utah. What varies is your own parcel.
Across Utah’s 29 counties the frost-free season runs from 98 days in Summit County to 237 days in Washington County — a spread of 139 days, which is why a single statewide planting date misleads. The median Utah county sees 175 frost-free days, leaving torenia about 95 days of slack on a typical parcel — room for a second sowing where the season runs long.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Torenia's 80-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Torenia draws honeybees and native bees (low value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, torenia can only work that bloom inside Utah's frost window — roughly 175 days, opening after the last 28°F freeze (Apr 12 - May 6) and closing at the first (Oct 8 - Oct 27), per NOAA Regional Climate Centers ACIS, 1991-2020.
Recommended Torenia Varieties for Utah
Utah publishes no state variety trial for torenia, so we won't invent a "best for Utah" list. Choose types rated to your USDA hardiness zone (4a-9a), and confirm winter survival and drainage against your own parcel.
Utah Cooperative Extension
For Utah-specific cultivar recommendations, planting calendars, and pest pressure for torenia, the canonical source is Utah State University Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Torenia native to Utah?
No — the USDA PLANTS Database lists Torenia as introduced rather than native in the Lower 48, so it is not part of Utah's native flora. It grows here as a garden plant; pairing it with a few Utah natives keeps local pollinators fed too.
Looking for plants that belong here? The Utah growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Torenia in Utah
When can I plant Torenia in Utah?
Utah's last spring hard freeze (28°F) clears between Apr 12 and May 6, and the first fall hard freeze lands between Oct 8 and Oct 27 (NOAA Regional Climate Centers ACIS, 1991-2020). Time outdoor planting to after the last hard freeze for your specific site — a further two to three weeks for anything tender — and count back from those dates for transplant scheduling.
Can Torenia mature before first frost in Utah?
Yes — Torenia matures in 65 days (USDA PLANTS Database), and Utah's dependable hard-freeze-free window runs 155 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 90 days of margin. Plant once the last hard freeze has passed — two to three weeks later for anything tender — and it ripens ahead of the first fall freeze.
What hardiness zone is Torenia grown in across Utah?
Utah spans USDA hardiness zones 4a-9a (USDA ARS PHZM 2023). Torenia carries a range of zones Data pending, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Utah site have?
A typical Utah site sees ~175 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Torenia needs 80+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date. In cooler counties like Summit, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Torenia native to Utah?
No — the USDA PLANTS Database lists Torenia as introduced rather than native in the Lower 48, so it is not part of Utah's native flora. It grows here as a garden plant; pairing it with a few Utah natives keeps local pollinators fed too.
How should I amend the soil for Torenia in Utah?
Torenia prefers pH 5.5-7 and well (dry spells) drainage (Growable Ground Plant Database). That sits in the common-ground band across Utah soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Torenia actually grow on my specific land in Utah?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores torenia against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in Utah
State-level data is a sketch. Your Growable Ground report scores torenia against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Utah torenia averages can't show:
We read public map data around Utah — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Utah torenia average
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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