The guys from apollo automation have some esp based hardware. You can always check the components used there and then select an ESP32 C6 since it has ZigBee connectivity.
Or of course just buy their stuff, I’ve been happy with it 
I’ve been reading this for a few days now, and I wanted to share these two sensors i found on Aliexpress, I haven’t tested but it looks like this might be it:
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I bought one (https://www.aliexpress.com/item/1005011551891552.html) two weeks ago. If I comapre it with Xiaomi mi plant sensor in same pot:
This sensor:
- fertility: 1024 μs/cm,
- moisture: 6% (it was not higher than 10%). Second comparision: 14% (no watering since)
- temperature: 22,9 °C,
- illuminance: 0 lux (highest value: 2500 lux at time), Second comparision 0 lux.
- humidity: 76%,
Xiaomi:
- fertility: 942 μs/cm,
- moisture: 38%, Second comparision: 38% (no watering since)
- temperature: 21,9 ° C,
- illuminance: 257 lux (highest value: 6000 lux at same time). Second comparision with Aqara illuminance sensor show 17 lux.
- humidity: this sensor does not have it but Aqara temperature 1 meter away show 60,2%
Not sure which moisture and illuminance is right. I do not know what would be battery life, yet. For now, looks promising.
I posted in this thread a couple of years ago when we were still prototyping, so I wanted to share a quick follow-up.
For transparency: I’m the founder behind Simpla Home.
We kept working on the idea and eventually turned it into a product called Soil X1, which is now live on Kickstarter:
It’s tested with Home Assistant/ZHA and Zigbee2MQTT, uses dual-depth soil moisture sensing and now runs on a replaceable AA battery.
This thread helped shape the device, so I’m curious what you think.
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Take my money (well, I guess you already did, because I pledged). I like the dual-zone sensing. What I really want is consistency across the devices. You may have seen my post (if not this thread, then somewhere in this forum) where I bought two of every Zigbee soil sensor I could find and stuck them all in the same pot, together. Many of the pairs would report quite different readings from each other.
Another thing I’d like to have is a reliable calibration procedure. Many of these sensors would report maybe 10% moisture when the soil was sopping wet and then go down to about 8% as the soil dried.
What would put you way ahead of the pack is to have some kind of temperature compensation. Most of these sensors change their soil moisture readings as the soil heats up and cools. This causes temperature-induced noise in the readings to be larger than the variance between wet/dry soil. Some people have proposed arithmetic functions to adjust the readings based upon the temperature that the sensor is reporting, but the temperature is measured at the surface, and the soil readings are affected by the temperature down in the soil, so there’s a time lag as the heat from the surface conducts down to where the moisture sensor is. I could write some Python script which tries to simulate the temperature at depth based up recent surface temperatures, but that’s a lot of work when it seems like the device should be able to compensate for this.
Lastly, please make sure that it has a reliable Zigbee radio. Many of these sensors drop off my network and I have to go out and re-pair them. It’s annoying enough when they’re all in a common pot. It would be a bigger pain if they were distributed out in my yard, somewhere.
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@Simpler you should consider shipping a couple free test samples with express to @GavinCampbell from the HomeTech.fm podcast (who just recently started his own YouTube channel called ”Gavin As A Service” as well) if you want an independent honest review of it, as listening to their last few years of podcast episodes it seem he have a really specialized in testing soil moisture sensors within the smart home niche, (though from my understanding he is only testing Zigbee devices with Zigbee2MQTT and not ZHA would not be representative to all Home Assistant users. Also be aware warned that one constant feedback he had to all manufacturers is that he personally wants a model that sits flush with ground so that he can use it anywhere in his lawn without lawnmower damaging it).
Anyway, I bet that it would be a good idea to also send free test samples with express to many smart home YouTube:ers that do independent products reviews of smart home tech to test and show if the device is actually any good, but I see that there is not a lot of time left for that now so you might be out of luck if you did not plan ahead for that before.
Regardless, you would probably want to get trustworthy independent reviewers showing of tests your devices on all or at least most of the popular smart home ecosystems with feature Zigbee gateway, and here on Home Assistant that deffinitly includes the built-in native ZHA integration (because that what most Home Assistant beginners start with and what many continue using if they have the official ZBT-2 adapter as their Zigbee Coordinator.
PS: @Simpler by the way, with your device being based on Zigbee a tip is to copy the essence of my Zigbee optimization guide for best practice tips for you FAQ on preparing for best possible experience and to avoid the downsides of the Zigbee technology, check it out here → Zigbee network optimization: a how-to guide for avoiding radio frequency interference + adding Zigbee Router devices (repeaters/extenders) to get a stable Zigbee network mesh with best possible range and coverage by fully utilizing Zigbee mesh networking
PPS: @GavinCampbell should make yourself read that guide too as I listened to you and your fellow HomeTech podcast co-hosts struggle with Zigbee devices yet I got the impression that ya’all do maybe not fully follow or are even aware of all those optimizations and best practices for Zigbee! 
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Hi!
@jemenake:
Thanks a lot for your pledge - and for the detailed feedback. I remember your comparison post.
For calibration, the current plan is to use the same simple per-device calibration approach as with Soil Pro: air = 0% and water = 100%. It gives us a practical baseline, although the absolute values will still depend on the soil type and installation conditions. User calibration is not planned for launch, but it is something we could consider later via OTA if there is enough demand. Consistency across devices should also benefit from this calibration approach and from the relatively wide measurement zones.
On temperature effects: yes, Soil X1 does include temperature compensation. In the “Stable trend” screenshot on the campaign page, you can see that the moisture readings stay relatively stable even though the temperature changes quite a bit between day and night.
And yes, I fully agree on Zigbee reliability. It is an important area for us.
@Hedda:
Thanks a lot for the suggestions and for sharing your Zigbee optimization guide. It is a helpful resource. I fully agree that independent reviews are valuable, and I also agree that ZHA matters a lot for Home Assistant users, not just Zigbee2MQTT. That is also why it was important for us to support both ZHA and Zigbee2MQTT.