I've spent a lot of time watching crop steering content. The "how we run our 10,000 sq ft facility" tours, the consultant walkthroughs, the cultivation director interviews. And every time, they get to the soil monitoring section and pull out the same thing: a Grodan Hugo sensor, or an Aranet Soil node, or a Growlink probe.
Then they mention the price — almost as an aside — and move on. $180 here. $300 there. And that's before the gateway, the cloud subscription, the proprietary software. By the time you're actually doing crop steering, you've spent $500+ per zone just to know how wet your substrate is.
Here's what they're actually measuring: volumetric water content. How much of your substrate, by volume, is water. It's a capacitance measurement. You stick two electrodes in the medium and measure how the dielectric constant changes with moisture. It's solved physics. Commodity hardware. A $15 Amazon sensor does the same thing.
Commercial soil monitoring systems run $180–$300 per probe before software. The underlying measurement — capacitance-based volumetric water content — is the same physics at every price point. TentPilot integrates two commodity sensor options for a fraction of the cost, with the same data, the same logging, and the same moisture-triggered automation.
What Soil Sensors Actually Tell You
There are three numbers that matter for crop steering. Here's what they mean and why you want them:
VWC (Volumetric Water Content): The core metric. What percentage of your substrate volume is water right now. In coco and rock wool, experienced growers target specific VWC ranges for each growth stage. Too wet and you restrict oxygen to the root zone. Too dry and you stress the plant. This number is the foundation.
Dryback: How far VWC drops between irrigations — usually overnight, or during the dark period. A bigger dryback pushes plants generative: more stress triggers earlier transition, tighter internodes, heavier fruit set. A smaller dryback keeps them vegetative: faster growth, more stretch. This is the actual lever in crop steering. Without a sensor, you're guessing.
Substrate EC: Only available from the wired sensor option below. Electrical conductivity in the medium. As plants absorb water but not nutrients proportionally, EC rises. Sustained high substrate EC signals salt buildup — time to flush, or dial back your fertigation concentration. It's the early warning system for nutrient lockout.
Two Ways to Add Soil Sensors
Both options integrate directly with TentPilot. The difference is what gateway they use and what data they provide.
Ecowitt GW1200 + WH51
- Up to 8 probes per gateway
- Wireless (433 MHz) — no cabling
- Local HTTP API — no cloud
- Reads: moisture %
DFRobot SEN0601
- Unlimited probes, daisy-chained
- RS485 Modbus RTU over USB
- Requires Pi Hub (Scout)
- Reads: moisture % + temp + EC
Option A: WiFi Gateway (Ecowitt GW1200 + WH51)
The fastest path to soil monitoring. The GW1200 gateway sits on your WiFi and serves a local HTTP API — TentPilot polls it every 30 seconds. No cloud account, no subscription, no data leaving your network. WH51 probes pair wirelessly in under a minute.
GW1200 + 4x WH51 = ~$90 total. A commercial system doing the same thing: $800–$1,400.
Option B: USB Gateway (DFRobot SEN0601 via Pi Hub)
For growers who want moisture, temperature, and substrate EC — or who already have a Pi Hub running TentPilot Scout. SEN0601 probes connect to a USB-RS485 adapter and daisy-chain on a shared RS485 bus. Scout discovers and polls them automatically.
Each SEN0601 ships with address 1. Configure a unique address on each probe before connecting them to the shared bus — address collisions will cause communication failures. See the Pi Hub setup guide for how to do this.
What TentPilot Logs
Both sensor options stream readings to TentPilot every 30 seconds. Every reading is stored. That's the part most growers don't realize they're missing until they have it.
Without a sensor, you stick your finger in the medium, make a judgment call, and move on. You have no record of how fast that pot dried out last Tuesday, or whether the back-left corner of your room is getting irrigated consistently, or how your dryback depth changed when you bumped up your light intensity.
With TentPilot logging your substrate, you get:
- Dryback curves per zone. See exactly how far VWC drops between irrigations and how fast. Know your substrate's behavior instead of guessing it.
- Zone-to-zone comparison. Running four probes? You'll immediately see if one pot is drying twice as fast as the others — channeling, uneven distribution, a bad drip emitter. Catch it before the plant shows symptoms.
- Stage-to-stage history. How did your dryback depth change from early flower to late flower? What did moisture look like the week before harvest? That data lives in TentPilot and informs every future run.
- Substrate EC trends (SEN0601 only). Watch EC climb over a multi-week run. Know when to flush before lockout happens, not after.
The first time you look at a dryback curve, you'll realize your irrigations were off. Either you were watering too frequently and never letting the medium dry back enough, or you were stretching it too long and stressing roots at the end. The chart makes it obvious. The fix takes 30 seconds in TentPilot.
Moisture-Triggered Irrigation
Timer-based irrigation is a compromise. You pick a time, you pick a duration, and you hope it matches what the plant actually needs. The plant doesn't care what time it is. It cares how wet the medium is.
With a soil sensor connected in TentPilot, you can replace the timer entirely. Set a threshold:
The plant drives the schedule. If it's a hot, high-transpiration day, it irrigates more often. If the room is cool and humid and the medium is barely moving, it doesn't irrigate at all. No over-watering on slow days. No under-watering when demand is high.
You can also layer conditions on top of the moisture trigger. TentPilot's rule engine lets you combine moisture with time-of-day logic to match how the pros do it:
- First irrigation of the day: Hold off until lights-on + 1 hour. Let the dryback run out fully before triggering.
- Last irrigation cutoff: No irrigations within 2 hours of lights-off. Give the medium time to dry back before the dark period begins.
- Generative push: Tighten the trigger threshold from 40% to 30% during weeks 3–5 of flower. Deepen the dryback to push the plant harder.
That last one is crop steering. And you just set it up with a $15 probe and a Rachio zone you already had.
How It Compares
| Capability | TentPilot Stack | Commercial System |
|---|---|---|
| VWC monitoring per zone | $15–$25/probe | $180–$300/probe |
| Substrate EC monitoring | Included (SEN0601) | $50–$100 add-on/probe |
| Historical logging | Included | Subscription required |
| Moisture-triggered irrigation | Included | $500+ controller add-on |
| Multi-condition rules | Included | Enterprise tier only |
| Cloud dependency | None (local API) | Required |
| 4-zone setup, total | $90–$130 | $800–$1,400+ |
The Same Loop. A Fraction of the Price.
The Grodan GRODAN system connects probes to a $600 GroSens gateway and a $500/year software subscription. Aranet Soil nodes pair to an Aranet4 base station and stream to their cloud platform. Both systems do exactly what TentPilot does: read moisture, log the data, and trigger irrigation when thresholds are hit.
The difference is they built the whole stack in-house — sensor, gateway, software — and they charge for every layer. TentPilot integrates commodity hardware that already exists and replaces the proprietary stack with software that's actually smarter.
Your plant doesn't know what brand probe is in its medium. It just wants to be watered at the right time. Now it will be.