Just checking the HA forums is this guy https://community.home-assistant.io/t/soil-humidity-sensor-433mhz-decode/202335

I have the whoffset AQI that has worked well, and I'm always looking to expand lol

I got some from Ali Express. They seem ok for the price. Dirt moisture and air temp and humidity. Dual AAA though so kind of large.

I use the ecowitt wh51, and they work pretty well. I have the 433mhz ones, but I’m using the ecowitt gateway, and not a rtl usb adapter.

They’re not that small though, but they run off a single AA battery, and the battery life is pretty good. Integrates well with home assistant.

@KayOhtie @homeassistant I saw a few custom ones on Tindie that looked nice and affordable. Havent made the purchase just yet.

Have a look on yoochoob for "the guy with the Swiss accent" (I forgot his real account name) - he did an interesting article on soil sensors.

I bought a zigbee sensor off Ali Express and it's fine, but it's waaay to.big for a small pot plant, but fine for a large one... so "big" vs "small" is kinda relative to the plant you're monitoring.

I have the ecowitt wh51, directly with rtl_433.
It's the 866 version.
I had to set rtl_433 to also monitor 866, but other than that, it's been very solid for...Blimey, years now.