If you've ever Googled "soil temperature" and gotten a weather site that gives you one number — a single point, no depth, no context, no forecast — you already know the problem. That number is barely useful. Seeds germinate at the surface. Roots live at depth. What's happening at 6 inches and 21 inches tells a completely different story than what's happening at the top of the ground, and neither one tells you what's coming next week when your actual planting window might open.
The right tool for soil temperature isn't a thermometer widget bolted onto a weather app. It's something built specifically for growers — something that understands that soil is a layered system, that conditions change hourly, and that the only question you're actually trying to answer is: is it time to plant?
Why One Depth Isn't Enough
Most casual gardeners, when they think about soil temperature at all, think about it as a single number. The air has a temperature, the ground has a temperature. Simple.
But soil is not a uniform slab. It's a gradient. The surface bakes in the sun and cools rapidly at night. A few inches down, temperature changes more slowly. Deeper still, it barely responds to daily weather swings at all — tracking instead with the weekly and monthly trend of the season.
This matters because different things happen at different depths:
- Surface (0–1 inch) — Where seed-to-soil contact happens. Germination temperature is a surface measurement. A tomato seed doesn't care what's happening 6 inches down.
- 2 inches — The critical root initiation zone for transplants. If you're putting a transplant in the ground, 2-inch temperature is what determines whether roots establish or stall.
- 6 inches — The active root zone for most vegetable crops. This is the depth that professional agronomists and extension services reference most often for crop guidance.
- 21 inches — Subsoil temperature. This tells you where the season is heading, not where it is today. Cold subsoil in April means cold surface soil in May. Warm subsoil in August means fall crops have a runway.
An app that only shows you surface temperature — or worse, estimates "soil temperature" by adding a fixed offset to air temperature — is missing most of the picture. You need the full profile to make good planting decisions.
When the 6-inch reading is still 10°F colder than the surface, you know soil is still warming from winter. When surface and 6-inch converge within a few degrees, you've hit peak spring warmth. That convergence is the signal most growers are waiting for.
App vs. Physical Probe: What the Data Actually Says
The old answer to soil temperature was a probe thermometer — a metal rod with a dial gauge that you push into the ground, wait 60 seconds, and read. They cost $12 to $15 and they work perfectly well. If you want a single measurement at a single moment at a single location, a probe thermometer is completely fine.
But a probe has real limitations that matter for modern growers:
- It only reads right now. No history, no trend, no forecast. You know what your soil temperature is at this moment, but not whether it's warming or cooling, or what it will be in five days when you're ready to plant.
- It only reads one depth at a time. Want the 6-inch reading and the 2-inch reading? Two separate insertions, two separate readings, and you need a probe long enough to reach the depth you want.
- It's point-in-time, not diurnal. Soil temperature fluctuates over the course of a day. A reading at 7 AM tells a different story than a reading at 2 PM. Without logging, you're working with a snapshot.
- It only works where you're standing. If you're scouting a second field, a client's property, or next week's planting site, you'd need to be physically there with your thermometer.
Apps like SoilIQ use NOAA and Open-Meteo soil model data — the same numerical weather prediction models used by agricultural extension services, commercial farms, and university research stations — to calculate soil temperature at multiple depths, updated hourly, for any location on Earth. You get trends, forecasts, and multi-depth data that a probe simply can't provide.
Model-based soil temperature data is consistently accurate within 1–3°F of a calibrated probe in normal conditions. For planting decisions — where the relevant threshold (say, 65°F for tomatoes) has a natural 5°F margin — this is more than sufficient. A physical probe and a well-built app are complementary, not competing.
What to Look for in a Soil Temperature App
Not all soil temperature apps are equal. Some are weather apps with a "soil temperature" module that's essentially an estimate derived from air temperature. Others source real soil model data but present only a single daily average with no depth breakdown. Here's what separates a genuinely useful tool from one that looks the part but falls short:
| Feature | Why It Matters |
|---|---|
| Multiple depth readings | Seeds germinate at the surface; roots establish at 2–6 inches. One number misses the story. |
| Hourly updates | Daily averages smooth out the diurnal swing that can be the difference between planting and waiting. |
| 14-day forecast | Lets you plan around your schedule rather than reacting to today's conditions. |
| Crop-specific guidance | Raw temperature data is useless without knowing what threshold matters for the specific crop you're planting. |
| Offline capability | Fields don't always have cell service. Cached data means the app still works when you need it. |
| Location flexibility | You should be able to check any field, any city, any property — not just your current GPS location. |
| Apple Watch / widget | Checking your phone in the field is friction. Wrist or home screen access is the right UX for growers. |
What SoilIQ Gives You for Free
SoilIQ is a free download on iPhone. No account required, no credit card, no trial countdown. The free tier is designed to give every grower the core information they need every day:
Surface, 2", 6", and 21" — all at once, updated hourly. Tap any depth to drill into the hourly chart and see exactly how temperature moved through the day.
A 0–100 composite score weighing temperature, moisture, trend, frost risk, and weather. One number that tells you whether your ground is genuinely ready to work.
Daily morning soil briefs, frost risk alerts the evening before, rain ahead warnings, and custom threshold alerts for any depth and temperature you set.
Search any city, farm, nursery, or address by name. Apple Maps POI support means you can find any location without knowing the coordinates.
Current soil temperature at your chosen depth on your watch face. No phone needed when you're working in the field.
Ask Siri "What's my soil temperature?" without opening the app. Pin a live small, medium, or large widget to your home screen.
Get live soil temperature at four depths — free.
No account, no trial, no paywall. Download SoilIQ and see your current soil conditions in under a minute.
What SoilIQ Pro Unlocks
SoilIQ Pro ($4.99/month or $29.99/year, 7-day free trial) is built for growers who need the full picture — not just today, but the next two weeks, across every crop and every field they manage.
14-Day Soil Forecast & Heatmap
The forecast tab shows daily soil temperature projections at every depth for the next two weeks, rendered as a heatmap so you can see warming and cooling trends at a glance. This is what separates reactive planting from planned planting. Instead of checking soil temperature every morning until conditions feel right, you can see on Monday that soil will hit 65°F by Thursday and plan your work accordingly. A frost risk timeline runs alongside the forecast so you can spot the last frost of the season before it passes.
133-Crop Planting AI
The PlantAI tab is the feature that makes SoilIQ genuinely different from any weather or soil app on the market. It analyzes current soil temperature, the 14-day forecast, and frost risk for your location — then produces a ranked planting window for every crop in its library, each with a confidence score.
Crops are organized into four categories based on current conditions:
- Ready Now — soil is at or above the ideal threshold for this crop today
- This Week — soil will reach the threshold within 7 days
- Coming Up — 8–21 days out; plan ahead and get your seeds or transplants ready
- Not Soon — soil is too cold or the season is too far out; don't waste time on these yet
The library covers 133 crops across 13 categories — vegetables, fruits, grains, herbs, grasses, cover crops, and more. Each crop has a research-backed soil temperature range, a base threshold for germination, and an optimal range for vigorous establishment. The AI doesn't just tell you whether soil is warm enough — it tells you how confident it is, and how long your window will stay open before conditions shift.
Because the AI runs against the 14-day forecast — not just today's conditions — it can tell you that tomatoes are 4 days away from ready, even if today's soil is still a few degrees short. That's a meaningfully different kind of planning signal than a probe thermometer can ever give you.
Field Journal with Photos
The Journal tab turns SoilIQ into a permanent field record. Log observations, note what you planted and where, attach up to four photos per entry, and add tags for crop, location, and conditions. Every entry is automatically stamped with that day's actual soil temperature and health score data — creating a ground-truth record tied to measured conditions rather than memory.
Over a season, your journal becomes something genuinely valuable: a year-over-year reference that tells you exactly what soil conditions looked like when your tomatoes took off, when your grass seed germinated in three days, and when the late frost you almost missed cost you a week's worth of transplants.
Unlimited Saved Locations
Free users get one saved location. Pro users get unlimited — switch instantly between your backyard, a community plot, a client's property, or a farm field twenty miles away. Each location maintains its own data independently.
Who SoilIQ Is Built For
SoilIQ was built for growers who take planting timing seriously — but "serious grower" doesn't mean commercial scale. It means anyone whose season depends on getting the timing right.
- Home gardeners who've planted tomatoes too early in cold soil and watched them sit motionless for three weeks while the neighbor who waited a week longer already has 6-inch plants.
- Lawn care professionals who need to know exactly when soil is ready for grass seed installation — and who serve clients in multiple locations across a region.
- Homesteaders managing a market garden or mixed planting where a dozen different crops each have different soil temperature requirements, and planting windows overlap in complex ways.
- Farmers scouting field conditions across multiple properties, who need reliable soil data without driving to every field every morning.
- Country club and golf course superintendents timing overseeding and turf establishment programs with precision.
What these users share is that they've stopped trusting the calendar. The calendar tells you what month it is. Soil temperature tells you what your ground is actually ready for.
How the Data Actually Works
SoilIQ pulls hourly soil temperature data from Open-Meteo — the same numerical weather prediction data used by meteorological services worldwide — at four soil depth layers that correspond to real agronomic measurement standards: surface (0 cm), 6 cm, 18 cm, and 54 cm (roughly surface, 2 inches, 6 inches, and 21 inches in practical terms).
The data is updated hourly from global weather models that are themselves validated against thousands of physical monitoring stations. When you set your location — whether by GPS or manual search — SoilIQ fetches conditions for your exact coordinates and caches them locally. When you're offline in the field, the last-fetched data is available immediately.
Model data represents soil temperature in open, relatively unshaded soil under average conditions. If you're in an unusually sheltered microclimate, growing in raised beds that warm faster than in-ground, or in an area with heavy canopy cover, your actual conditions may differ from the model by a few degrees. A physical probe reading periodically is still the gold standard for calibrating your intuition against the data.
SoilIQ also includes a probe calibration feature — enter a reading from your physical thermometer at any depth, and the app applies that offset going forward. This gives you the best of both worlds: the trend, forecast, and crop guidance of a model-based system, grounded in your actual measured conditions.
Apple Watch, Siri, and Widgets
Friction kills habits. If checking soil temperature requires pulling out your phone, opening an app, waiting for data, and then navigating to the right depth — it won't become a daily habit for most growers, no matter how good the data is. SoilIQ is designed to meet you where you already are.
Apple Watch: Current soil temperature at your selected depth appears as a Watch complication — visible on your wrist face without a tap. In the Watch app, you get the full four-depth readout, moisture level, and health score without ever touching your phone.
Siri: "Hey Siri, what's my soil temperature?" works without unlocking your phone. SoilIQ's App Intent responds with the current reading at your active depth and location. For growers who move fast, this is how the app gets consulted dozens of times a week instead of a few times a season.
Home Screen Widgets: Small, medium, and large widget sizes let you pin current conditions directly to your iPhone home screen. The large widget includes a five-day forecast bar chart — a quick visual of where soil temperature is headed over the week.
Live Activity / Dynamic Island: When enabled, SoilIQ runs a live activity on your lock screen and Dynamic Island, showing the current temperature and trend without unlocking your phone.
Check your soil without opening the app.
Ask Siri, glance at your widget, or check your wrist. SoilIQ is built for the way growers actually work.
Frequently Asked Questions
Is there an app that shows soil temperature?
Yes. SoilIQ is a free iPhone app that shows real-time soil temperature at four depths — surface, 2 inches, 6 inches, and 21 inches — updated hourly from global weather models. It works for any location on Earth without a hardware sensor.
How accurate is a soil temperature app without a physical probe?
Apps that use NOAA or Open-Meteo soil model data are consistently accurate within 1–3°F of a calibrated physical probe. The models are trained on data from thousands of ground-truth monitoring stations and updated hourly. For planting decisions — where a 5°F margin is what matters — app-based data is more than sufficient. SoilIQ also supports manual probe offset calibration if you want to lock the data to your exact measured conditions.
What is the best free soil temperature app?
SoilIQ is free on iPhone and shows soil temperature at four depths, a Soil Health Score, hourly chart, Apple Watch complication, Siri shortcut, and home screen widgets — all without a subscription. Pro unlocks the 14-day forecast, 133-crop Planting AI, Field Journal, and unlimited saved locations.
Can I check soil temperature from my iPhone without buying a sensor?
Yes. SoilIQ uses global weather model data — the same data source used by agricultural extension services and commercial farms — to calculate soil temperature at multiple depths for your exact location. No hardware required. The app works anywhere in the world with a location signal.
Does SoilIQ work outside the United States?
Yes. Open-Meteo provides global coverage. SoilIQ works for any location on Earth — search by city name, address, or let GPS find your current coordinates. The 133-crop AI and all other features work regardless of country.
What's new in SoilIQ version 2.0?
Version 2.0 is a complete native rebuild — the app was rewritten in SwiftUI from the ground up and is now faster, works fully offline, and adds several major features: the Soil Health Score, full place search with Apple Maps POI support, the Field Journal with photos, probe calibration, and expanded Apple Watch and widget support. The PlantAI engine was expanded to 133 crops with per-crop confidence scoring.
The best gardeners, farmers, and turf managers in the world share one habit: they watch the ground, not the calendar. Air temperature fluctuates wildly. Calendar dates are averages of averages. Soil temperature is the actual signal — the measurement that seeds, roots, and pathogens all respond to directly. An app that gives you that data, at depth, with a forecast and crop guidance, pays for itself the first time it keeps you from planting into soil that isn't ready.
Stop guessing. Start growing with your soil, not against it.
SoilIQ is free on iPhone — four depths, hourly updates, and a clear signal when your planting window is open.