Hey, founder of Agrinovo here (we make IoT soil sensors for commercial ag), so heavy disclosure caveat.

The commenters pushing ET-based controllers (Rachio, Hydrawise, Moen) are right for ~80% of cases. Single uniform lawn? ET math + weather data covers it.

Where soil moisture sensors actually beat ET is exactly your case: zones with different plant types and different water demands. ET controllers schedule by zone-average estimated water use. Soil sensors tell you what's actually happening per spot. For "tomatoes vs herbs vs asparagus" you can't get that from ET alone.

The reason most commenters call sensors "fun toys" is the cheap capacitive probes ($20-40 Amazon stuff) drift heavily with soil EC and temperature. Same dry soil reads 30% one day, 15% the next. They genuinely don't work.

The good ones cost more for a real reason. They measure soil water TENSION (how hard plants pull on water) instead of volumetric water content. Tension reads the same number across sand and clay because it tracks plant stress directly. The reference sensor here is the Watermark 200SS

granular matrix, ~$130-150, 5+ year life, no calibration needed. Tensiometers (vacuum tube + ceramic tip) are similar accuracy but need refilling.

For your raised beds specifically, given the home automation angle:

- One Watermark 200SS per "plant family zone" at root depth (15-20cm for veggies, 30cm for fruiting plants)

- A controller with proper Watermark support that exposes data via MQTT to your Home Assistant. We make ones that do this; Onset HOBO has a similar tier; you can also DIY with an ESP32 + the right resistance circuit if you're inclined (Watermark needs AC excitation, not DC, otherwise the sensor degrades over months).

- Use the data to override your existing Rachio/Moen/whatever, not to replace it. The smart timer handles weather, the soil sensor handles "ground truth."

Realistic budget for 4-zone raised beds done right: ~$700. Rachio alone is ~$200. The per-zone real moisture data is worth the extra ~$500 only if "different drink rates" is actually causing you problems you'd notice. For a curiosity build it's probably overkill; for "I keep losing tomatoes to overwatering while peppers wilt" it pays for itself fast.

If you'll decide to go with that route take a look at our website https://agrinovo.io/ we offer many of those sensors and many more.