In uk.d-i-y, Timothy Murphy wrote:
What is the best way to set up a system
for watering a garden every 2 or 3 days, say?
Can one buy devices that do this?

Also, is there any simple way of setting this up
so that it can be activated remotely by computer?

Hozelock and Gardena make all the bits. I usually recommend Hozelock
because they're more widely obtainable at B&Q, garden centres, etc. The
timers are quite simple but I've not seen any that can be remotely
controlled (though ground-moisture-sensing is an option with Gardena at
least). Just add wide-area sprinklers. If you want to water individual
tubs etc, you'd use a low pressure system with a network of mini tubes
and sprinklers. There are a lot of options there and it can seem a bit
daunting at first but once you get started it's a doddle. You can get
"starter kits" containing the bare essentials then supplement it with
extra components when you've worked out what you need.

--
Mike Barnes