They like a warm position in full sun in well drained soil. Plant the rhizomes so that they face south and as you said, with the top of the rhizome on the surface.

Thanks Owdboggy.
The other ones were more like bulbs and I planted them deeper than that; how do you know which type of Iris needs to be partially exposed/beneath the ground?
Thanks again
Charlie

Hard one to answer, there are various types of Iris from ones which grow in water to ones which need desert conditions.
Basically, the ones which most people grow come into three groups, ones with a bulb and ones with a rhizome and ones without either. The bulb is round ish (often pear shaped) with a netted covering. These you plant deeply. Dutch, Englsih, Spanish, Irises are all bulbs as are I. reticulata (George is my favourite).
The rhizome is usually supplied with a few roots coming from the base, it does not have a netted covering. These are surface planted. Things like Iris germanica, the bearded Irises have rhizomes.
Finally there are the Iris sibirica types which do not apparent bulbs or rhizomes. These are planted at the depth which they were supplied.
Actually all you need to do is read the packet.

I appreciate that, thank you. I did refer to the label on the pot (they're quite large plants, one of them already in flower) but there was no instruction as to planting depth.
Thanks again
Charlie

Well, if you get stuck, you can always ask on here. Lovely plants though. We have a fairly large number of different Irisies. Look out for Iris Pacific Coast hybrids, they are small and come in some very delicate colours. We have one which is basically apricot and peach.

That sounds beautiful; would love to see a photo. My mum and I went to Chelsea for the first time and the Iris were amazing. So many varieties and colours. I've always failed with them until this year (clearly because i didn't understand the different varieties needs!) so I'm looking forward to adding new ones and will be looking out for the Pacific Coast Hybrids.
Charlie

Broadleigh Bulbs used to sell them, not looked at their catlogue recently though. If you look in my Blog The Garden in June, about half way through is a picture of the Iris.