Aloha Chris,

First welcome. Please clarify what you mean by semi-automatic irrigation. Usually a system is set up so that you don't have too worry about remembering to water your plants. You do have to adjust the automatic settings for the growth stages of your plants and time of year every so often. Your system has a controller(Timer) to set areas or zones that you want to water. A controller can take care of a various number of zones depending on the controller you buy. It also lets you select the time of day and the duration of the watering you want to do. The amount of water is determined by the size of the emitter you use and how long you run your system(duration)per cycle. You then figure out how many cycles you run per week, by how much water your plants need per week. You shut your system down when it rains manually or pay more for an automatic rain sensor wired to your controller. You can run your system manually to give more water than the system provides. You can buy a controller that fits on your hose faucet and is battery operated. That is the basics. I hope I answered your question without much confusion. Just ask more questions to clarify what is confusing. Aloha

*"Do you set up the water supply so that the emitters are dripping constantly, or do you set it to supply periodically?
* Any thing is possible but usually they run just enough to put down the quantity of water you want. Most use timers, but myself, being different, I run mine manually. I have 2 gal per minuted drippers at my tomatoes so every morning while I walk around, I turn them on for about 15 minutes. That gives about half a gal..You get the idea.

I meant to say 2 gal per HOUR not per minuet.

chriscarless, I cannot think of a greenhouse environment which would require constant drip irrigation. I would quantify the water needs of the pots, ascertain the output of the emitter to the pot and run the system long enough to supply the quantity of water. You will have to determine the irrigation interval (period) - daily? every other day? weekly? etc.
You can turn the system on and off manually like colokid does or you can have a timer do it for you. Manual is straightforward; automatic is fun.

Thanks, guys, that sorts me out.

What I meant by semi-automatic is that I'm happy with a system where I can turn a tap on to set it going then turn it off later, monitor the weather to get the watering right etc, rather than something I can leave alone for weeks at a time.