At the Salt Lake City reference station, the last spring freeze lands between April 12 and April 29, and the first fall freeze between October 18 and October 29. Hardy unusual roots like salsify and burdock go in as soon as the soil is workable. Tender ones wait until after the April band closes. Those dates describe a mild valley, though, and most of Utah is colder.
The short answer for Utah
Plan around two windows: April 12 to April 29 for the last spring frost, and October 18 to October 29 for the first fall frost. Both come from NOAA’s 1991-2020 Climate Normals for the Salt Lake City station. Neither is a promise. Each marks the 30 to 70 percent band of probability for a 32°F freeze, so a freeze after April 29 or before October 18 is still a live possibility in any given year.
That distinction changes how you use the calendar. A date in the middle of a probability band is a coin flip, not a guarantee. Hardy roots can absorb the gamble because their seed and young seedlings tolerate a light freeze. Tender roots cannot, so they should wait for the far end of the band, and then some.
| Type of root | Examples | When to plant at the Salt Lake City reference |
|---|---|---|
| Hardy, slow, direct-sown | Salsify, scorzonera, burdock, parsnip | As soon as the soil can be worked, ahead of the April 12 to April 29 band |
| Hardy tubers and perennial roots | Jerusalem artichoke, horseradish | Early spring, same logic as above |
| Frost-tender or transplanted | Celeriac, oca, yacon | After April 29, once nights have settled |
| Fast fall roots | Daikon and other fall radishes | Late summer, counted backward from October 18 |
Between the two bands, the reference station has roughly 172 to 200 days from the last freeze to the first. That arithmetic comes from the dates above, and it is a ceiling, not a target. Roots that sulk in cold soil, or that need most of the season to bulk up, use a large share of it.
For fall crops, work backward. Pick October 18 as your deadline, subtract the maturity time printed on the seed packet, then add a couple of weeks for the slower growth of shortening days. Whatever date that gives you is the last day to sow, not the best one. For a fuller rundown of which roots suit these windows, see The Best Unusual Roots to Grow in Utah.
What will not work here
The slowest roots are the first casualties of a short season. Salt Lake City is the mild case, and the reference station’s own caution is that most of Utah sits higher and colder. If the valley floor gives you about 172 to 200 days between freezes, a garden at altitude gives you fewer. Anything that wants nearly the whole season to size up, such as oca or yacon, can be cut off by an October freeze before it has stored much. Those two are tropical-highland crops that form their harvest late, and they are a poor bet where fall arrives early.
Overwintering tender roots in the ground
The coldest month at the reference station averages a daily minimum of 24.2°F. That is the mean low, not the record, and it decides what survives winter. Hardy roots like horseradish, burdock and Jerusalem artichoke handle it without trouble. Tender tubers do not. Leave yacon or oca in the bed through a Utah winter and expect mush by spring, so lift and store them instead. The 24.2°F figure is for the valley, and the cold gets worse as elevation rises.
Weekly watering and slow seed
This page’s facts do not include rainfall or summer highs, so no rainfall numbers are offered here. What can be said without them is that Utah gardeners who water on a once-a-week habit tend to see the damage in root shape. Salsify, scorzonera and parsnip all react to swings between dry and soaked soil by forking, splitting or turning woody. A deep soak followed by a week of baking is the pattern to avoid. Slow-germinating seed is hit hardest, because a crust that forms over the row can keep tiny seedlings from emerging.
Two more mistakes are worth naming. Planting tender roots on April 12 because the calendar says the freeze might be over is one. The band’s lower edge means a roughly 30 percent chance that a freeze is still ahead, and one night can erase a bed of transplants. Sowing fall radishes in September is the other. By the time they size up, the first freeze is days away.
If you are starting from scratch, the pattern that holds up is simple. Keep the slow, hardy crops in the ground early, hold tender crops back until the band is well behind you, and treat fall sowings as a race against a date you can already see. The broader picture of what to grow sits in Growing Unusual Root Crops in Utah.
What changes across Utah
Utah does not have one answer. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places the state anywhere from zone 4a to zone 9a. That is a spread of six full zones inside one set of borders, and it is why a calendar built on Salt Lake City cannot be copied across the state.
The USDA system rests on one variable only, the average annual extreme minimum temperature. It tells you whether a perennial root like horseradish or Jerusalem artichoke will survive winter. It says nothing about how long the growing season is or how hot the summer gets. Two gardens in the same zone can have frost dates a month apart, so treat the zone as a winter-survival label and the frost dates as the planting guide.
For a reader in the north or at altitude, the shift runs one direction. Move the spring sowings later, because soil stays cold and the last freeze arrives after the April 12 to April 29 band. Move the fall deadline earlier, because the first freeze arrives before October 18. Favor hardy, shorter-season roots, and think twice about anything tender. The reverse holds in southern Utah, which the reference station’s note describes as warmer. There, spring windows open earlier and fall ones close later, so tender roots get a better shot and fall sowings can run later.
Do not guess which zone you fall into. The USDA zone map lets you enter a ZIP code and read your own zone, so use it, and then compare it against the 4a to 9a spread above. If your zone sits near the cold end, treat every date on this page as a starting point to push later in spring and pull earlier in fall. If it sits near the warm end, you have more room than the Salt Lake City numbers suggest.
Where to check this for your own county
Your state extension service is the next stop. For Utah that is Utah State University Extension, the land-grant university’s outreach arm. County offices work with growers in specific valleys and elevations, so they hold the local knowledge that a single reference station cannot.
Two things are worth looking for there. The first is a local planting calendar, ideally one that lists frost dates for your county or nearest town instead of the state at large. The second is the list of varieties trialled in your county, which tells you what has been grown to harvest under your conditions rather than what a seed catalog claims. Many unusual roots have little formal trial data, so an empty result for salsify or scorzonera is possible, and it is fine. In that case, look at what extension recommends for closer relatives, such as parsnips or carrots, and borrow the timing logic.
Be plain about the hierarchy. A county recommendation beats a state one every time, and this page is the state one. It rests on a single station in a mild valley and a single set of freeze probabilities. It can tell you how to think about the calendar, but it cannot tell you the frost date for a neighborhood at 6,000 feet.
If your county office offers a phone line or a garden help desk, a short question will often do more than an hour of searching. Ask when the last spring freeze tends to occur in your area, whether anyone nearby has grown the root you are considering, and what soil problems to expect.
Checking this against your own garden
Your own garden outranks every date above. Three observations cost nothing and need no equipment.
- Soil warmth by feel. Push a bare hand into the bed in the morning. If it feels cold enough to ache, tender roots and warm-season transplants should wait. Beds that feel noticeably warmer earlier, usually ones against a south-facing wall or raised above grade, tell you that you have a warmer pocket and can lean earlier.
- The first male flowers. Squash and cucumbers send up male blooms before female ones. When they appear in your garden, nights are warming and the season is turning. If they come late compared with neighbors, your spot runs cool, and that argues for shorter-season roots.
- The first true leaves. Seedlings first show rounded seed leaves, then the shape particular to the plant. Quick, steady true leaves mean the soil and air suit the crop. Slow, stalled or purple-tinged ones suggest cold ground, so hold back the next sowing.
Write the dates down each year. After three seasons, your own notes will be a better local calendar than any station.
Common questions
Can I plant unusual roots before the last frost in Utah?
Hardy ones, yes. Salsify, scorzonera, burdock and horseradish can go in as soon as the soil is workable, ahead of the April 12 to April 29 band at the Salt Lake City reference. Tender roots like oca and yacon should wait until after April 29.
Do the Salt Lake City frost dates apply to the whole state?
No. The reference station sits in a mild valley. Most of Utah is higher and colder, and southern Utah is warmer, so shift your windows accordingly and confirm them locally.
What do the frost dates on this page actually mean?
They mark the 30 to 70 percent band of probability for a 32°F freeze, from NOAA’s 1991-2020 Climate Normals. A freeze outside the band can still happen.
Which USDA zone is Utah in?
All of them from 4a to 9a, according to the USDA Plant Hardiness Zone Map 2023. No single zone covers the state, so look up your ZIP code on the USDA map.