Lots of questions there. First of all first year Irises do not need splitting up. Next year maybe, if the rhizomes are overcorwded. Resons for non-flowering are many, but take your pick from, 1 too young, 2 underfed and 3 lack of sunlight on the roots last Summer.
2. Feed with Maxicrop about now and Tomato type food in early Spring.
3. Move to a sunnier place. Or if the rhizomes are overshadowed or facing the wrong direction, change that. They should always be planted sp that the rhizomes are exposed to as much sun as possible.
Next, o;d flowering stems. Cut the stem itself off back to where it emerged from the leaves. Clean up and remove and dead or dying leaves and you can if the tips are going brownl cut of the tops of the leaves, but to no more than half their length. The plant needs them for food production.
Gladiolus bulbs may be left in ,if you are on a well drained sandy soil and they were planted deeply enough for frost not to reach the corms, otherwise dig up and store over winter for replanting in Spring.
Berghill is right if these are flag irises-Petew- if they are dutch irises they can stay in-what sort did you plant do you know?
I was told to expose the rhizomes and not to plant them too deeply . Hope that was the correct information - mine were split last year and didn't flower so I'm hoping they will do better next season . They've always flowered until I split them and are in a sunny spot and well fed so I'm keeping my fingers crossed.
I am unsure as to the type but have many different colours eg. blue/yellow, brown or black/yellow/purple, white with a touch of yellow. Don't know if they are flag or dutch?
Flag irises have a thick root-a rhizome-and broad leaves-a bit like flags