Growing up we always had a garden. This meant fresh veggies and tasty fruit throughout most of the year. And even though I never had a cliché hatred for anything green, I never really appreciated this either. It was just normal.
Moving into a city really changed that, and spoiled me realized that not everyone has a garden. Nor parents that spend loads of their free time dealing with it. So while I’m grateful in retrospect at least, that still does not bring back that tasty salad from back in the days. What does not help either, is that I’m already annoyed by the repetitive watering chores for the few plants that actually do live on our balcony at the moment.
In comes TheStockPot. A youtuber that, among other cool stuff, build a smart greenhouse. While I’m sure he is not the first one with this idea (in fact the farmBot has been in my head for years), it’s his video that sparked my motivation. So if you like watching videos, this is where you should leave the post and just watch the video instead. All the credit goes to him and all I have to add will be some tinkering with electronics from a beginners POV. And some woodworking.
The idea
If you are still here, the idea is pretty straight forward: Take (or build) a greenhouse, lob some sensors in there, add a water pump, connect everything to Home Assistant and get an infinite supply of vegetables without spending time watering or going to the supermarket. So like any sane person, I ignored all the financial and time consumely implications and set out to build something alike.
The hardware
The system is based on an esp32 board with relays. A microcontroller with wifi that nicely integrates into Home Assistant.

The relays allow supplying any odd electrical device with up to 230V. The "original" uses them to power heating mats to better manage the temperature inside the greenhouse (which I don't). I used it because I didn’t think and just did what the video did. Actually I currently only use it to power one 12V pump. Speaking about 12V: I picked a 12V membrane pump since the board also takes 12V. This way I only need to run one power cable and there is no need to mess with high voltage. For sensors I used a DHT11 (air temp and humidity) and multiple DS18B20 (soil temp). Since I don't run active heating (or cooling) atm, these are not really required. They were wired in because they are cheap and I like data (and heating might get added, who knows). Lastly there is a simple float switch to turn off the pump when my water container runs low (I don't run tap water).

Everything is stuck together with some resistors on a prototyping board, which I did for the first time. It was super doable for a solder beginner, and I learned quite a bit! Sticking multiple sensors together and supplying things with power made me think about what's going on and how to get everything connected with as little mess as possible. Way more interesting (and challenging) than following some laid out tutorial.
Don't solder everything to the board but make it disconnectable would be my own thought to share, for everything else there is more qualified people out there.
The software
ESPHome is super cool! If you run Home Assistant and want to integrate some custom devices, definitely give it a look. It’s a convenient and easy way to program your hardware. One maybe helpful note: Starting out I ran the ESPHome Device Builder on my Home Assistant instance (= a Raspberry PI 3). Compiling was really hard on that little guy and took forever. I switched to running a container on my local machine which made the whole process a lot quicker. Also make sure you have access to a USB to TTL adapter to program your board. Regarding the code I’ll happily point you to TheStockPot blog, which I used as a base for my own greenhouse. Biggest change I made was to remove the heating and add a float switch that prevents misting when the water is low.
In addition to that, I added a temperature sensitive automation in Home Assistant. Every time the temperature falls below 3 degrees C it disables the pump. This way I hope to prevent it running when things start to freeze.
The woodware
Building the frame from wood has the obvious downside that it will probably likely rot and the upside that it was free. Most pieces are planed roofing timber that I notched on the table saw. Notches for the windows were also cut on the table saw. Other than a little miscalculation in the width, everything went smoothly.

Throw in some preowned hardware, and this was the cheapest part of the build. One of those cheap, plastic skinned houses would likely do just as well (likely better due to better isolation), but where is the fun in that?
The résumé
Like (almost) always: It was a fun journey! Like also almost always: It was pricier than expected. Other than the controller and sensors listed above, I spend quite some money on other electronic related items (enclosure, prototyping board, wires, standoffs and other tiny bits). So from a financial standpoint, I don't think it'll pay for itself any time soon (in particular since I already have a version 2 in mind).

From a non financial standpoint it was (and is) a super enjoyable project! Starting with the first click of the relays, to wiring with a prototyping board, to checking my PlantStats™ every day, to watching my little plants grow. There was tons to learn and there is tons to improve! Some in this version some in the next. I still have to work on the watering schedule and the perfect placement for my misters. Also I might need to seal my housing a little better.