Iris Germanica - bulbs or rhizomes?

[Rossa]

I was given some iris germanica for my birthday. The packaging isn't very helpful about planting them. It says they are bulbs and should be planted 4" deep but when I opened the pack they look like rhizomes.

As far as I know if they are rhizomes rather than bulbs they need to be planted just below the soil level or with a bit showing where the new growth is. Is this right? They are long tubers with 6-8" roots rather than bulbous so I hope I've got this right and they are rhizomes.

I sort of remember that some Irises like acidic soil. Is this true for all Irises? If so should I use ericasaeous compost (can't spell that one after 2 glasses of red wine...lol) mixed in with the soil?

Any advice please?
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"..I went from adolescence to senility, trying to bypass maturity.." Tom Lehrer

[coreopsis]

You are right,Iris Germanica has rhizomes,not bulbs.4" under the ground is too deep,I would go for half of that at most or like you said just under the soil.Once established they haven't got any special requirements(partial sun)and they will happily grow almost anywhere.