# How do I position my substrate probe in a large no-till or living-soil bed?

In large no-till or living-soil beds (12–24″ / 30–60 cm tall), vertical and horizontal positioning make a big difference.

### Best single-sensor placement

Place the probe **25–35% of the bed height below the soil surface**.\
\
This corresponds to roughly:

* 4″ / 10 cm deep in a 12″ (30 cm) bed
* 5–6″ / 13–15 cm deep in an 18″ (45 cm) bed
* 6–8″ / 15–20 cm deep in a 24″ (60 cm) bed

This depth represents the **active root zone**, where the plant takes up most of its water and nutrients. 

It’s ideal for monitoring crop steering, drybacks, and irrigation timing.

### Two-sensor placement (recommended)

Soon, the Grow Sensor PRO will support up to 2 substrate sensors per unit (28/10/25).

If your bed allows for two sensors, you’ll get the most complete picture by tracking both the upper and lower moisture zones:

* **Upper sensor (plant-active):** 25–35% of the bed height below the surface\
       → **Used for crop steering and monitoring drybacks.**
* **Lower sensor (drain/leach):** 3–4″ (8–10 cm) above the bed bottom\
       → Used to **track salt build-up and leaching** near the base of the bed.

Even in taller containers, placing the lower probe 3–4″ from the bottom keeps it just above the saturated zone, which forms at a similar height across most soil mixes.

### Horizontal position

* Place the probe **halfway between plants and between emitters**, within the main wetted zone but **not directly under a dripper.**
* Stay at least **4–6″ (10–15 cm) away from the bed’s fabric sidewalls** to avoid edge drying that can skew readings.

### Orientation

* Insert the probe with the **prongs parallel to the soil surface**, level and fully buried.
* Ensure **firm contact** with the soil — no air gaps.
* Measure depth from the **mineral soil surface**, not from the top of any mulch layer.


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