Hi!
This year I got myself a new greenhouse.
Because I needed a simple irrigation system I first started with a two timers and a relay module.
CD4060 for the 12/24 hour timer and a 555 for the pump timer.
It worked but was not so simple and I missed a display.
So I changed my mind and switched to a MCU design.
The system is very simple:
Atmega8 for brain 
Code only use 2700 bytes flash and ~77 byte RAM.
I would recommend a Arduino pro mini if you don't have Atmegas around.
One switch for choosing 12/24 hours between watering.
One button to manualy start watering (and reset the 12/24 counter).
One trimpot to set pump timer (1-30 minutes).
Display TM1637 - Shows:
Default countdown until watering
12/24 hours if switch is changed for 10 seconds.
Minutes 1-30 if trimpot changes for 10 seconds.
Pump countdown when watering starts.
I used a regular garden hose that I drille holes in. The holes are larger at the end to compensate for the falling water pressure.
After my first try the water continued to flow even after the water pump was off because of the gravity
I then added a solenoid valve to stop the water.
Works good now.
I attach some pictures of all the parts. I power the system with solar cells and a 12V lead acid battery.
The charger and battery is mounted in a toolbox. I also have a 5V regulator in the toolbox for the Arduino.
/Olof
