If you are fairly tech savvy, this isn't hard to do.

I have built a few sprinkler valves using an esp8266, relay, solenoid, and esphome. Total cost of each one is less than $15 (US). If you are willing and patient, you could probably get that to under $10 via aliexpress.

The circuit is really simple -

Parts list:

• 12v power supply
• DC to DC converter
• Microcontroller (esp8266 or esp32)
• 5v relay
• 12v solenoid valve
• Plastic enclosure (use old Tupperware or 3d print something)

Outline:

• Run power supply to dc-dc converter, and set converter to output 5v.

• Connect one leg of 12v through switch on relay, then to the solenoid.

• Connect other 12v leg directly to solenoid.

• Run 5v from output of buck converter to input of esp and relay.

• Run data wire from esp pin to data input in relay.

• Put everything but the solenoid in a plastic box.

• Run water source to solenoid inlet and connect sprinkler or drip system to solenoid outlet.

• Flash esp with esphome

• In the esphome code, you will need the home assistant api, a switch, and a sprinkler component.

• In home assistant, set a switch or button on your front end to test everything with and provide manual control

• Write a basic home assistant automation to control via timer, or weather conditions, or soil hydration, or whatever.

You can do all of this without any soldering or any (real) programming - that being said, those two skills will improve the results by quite a bit, and are just useful in general for this sort of work.

It can (of course) get as complex and full featured as you like, but if all you want is a system that can water your flowers every time the ISS passes overhead, the above will get you there pretty cheaply.

I've used these before, and I think they have a multi-valve as well.:

https://www.amazon.com/dp/B0758NR8DJ https://github.com/sebr/bhyve-home-assistant

Not much less than the Rachio though.

Woox r7060, ZigBee and button controlled, 35€

Was easy to integrate and is operating flawlessly since a couple of months.

https://www.reichelt.de/smarte-bewaesserungssteuerung-zigbee-woox-r7060-p298801.html?CCOUNTRY=445&LANGUAGE=de

I just added a zigbee valve controller. I almost got the rachio version also when it was on sale for $80 but decided to try something else in case I wanted a second one later.

This is the version I got and it’s been working without a problem for a month now.

https://a.aliexpress.com/_mrn97Kq

I use the b-hyve, but it's also not cheap.

I am using BQ05 valves flashed with Tasmota: https://templates.blakadder.com/irrigation_timer_BQ05.html

They have been running drip irrigation for my raised beds for a couple of weeks now. Their wifi is kind of weak though, I needed to install an outdoor repeater to improve connection stability.

Edit: Using MQTT the valves appear als simple switches in home assistant and are easy to automate.

Orbit BHyve is a range of smart retic products that can be controlled by HA. I use their retic controller.

I use irrigation and honestly, dont see the merit in dynamic control. Some el' cheapo timers off Amazon switch the water on and off on a schedule. Yeah maybe you want to worry about rain days, but to me I don't really care, whatever they get more water. I'd rather spend that home automation budget on something more useful to me.

I'll second the Zigbee valve, I got mine on AliExpress for about 50$ CAD. It's a big gray thing with a button on the side, it looks like it's all the same model. It exposes a switch in HA, on when the water can flow, off when it can't. Pretty easy to automate.

In australia there is a brand called Holman which does WiFi enabled smart valves. Starting at battery powered valves you attach to the tap all the way up to full solenoid valves which need a controller. There is then the Holman app which hooks into your home automation suite.

Not sure if it's available in the US, and any mains powered unit would be on a different voltage. But the battery powered ones seem OK. Just chews through a lot of batteries apparently.

I have the Holman WX 8 controller paired with a bunch of online solenoid valves. It is a decent setup although quite expensive and took a long time and lot of effort to set up (running lines to solenoids, setting up water lines, dripper hoses etc) . It makes a huge difference in irrigation tho. Absolutely zero effort to get water exactly where the plants need it. Id say I broke even on effort the first summer. Cost wise longer term.

I have one of these, but it was a pita to set it up...

I'd have some hesitation to tag those in due to the number of times I've had internal hose splitters/timers get broken or worn out, and develop a leak. It's no big deal if I'm replacing a $10 splitter, but it would sure sting when that $76 controller develops a leak.

I was looking for ZigBee valves before but didn't find anything. I was also considering using an Arduino like board with ZigBee and making my own but never actually got around to it. My plants all died when work picked up but I might be trying again once work things stabilize

Buy a relay board and an ESP8266/32, flash Tasmotaon it (or them) and you're done! You can control them with HA through MQTT.