Iris would have to be one of my favourite plants. I grew up with them in the garden, and my Mum and i used to have alot of fun searching for new varieties.

Bearded irises (sometimes sold as Iris germanica cultivars) have large fleshy stems (rhizomes) at soil level and flowers with soft hairs (the ‘beard’) on their lower petals (falls).

Lift and divide rhizomatous bearded irises every three to five years. Although they can be happily divided once a year (depending on how quickly your Iris are multiplying)
This is ideally carried out six weeks after flowering, to give sufficient time for the plants to produce new growth for the following season before they enter winter dormancy

DIVISION:

Cut away each fan of leaves from the clump, using a sharp knife. Each fan should have a portion of young rhizome (up to 15cm/6in long for tall bearded irises, smaller for miniature tall bearded irises)
Select the largest fans with the healthiest rhizomes
Discard smaller fans and old, withered looking rhizomes
Shorten the leaves to about 15cm above the rhizome and trim the roots to shorten them

REPLANTING:

Dig a hole, large enough for the rhizome and roots, mounding the soil slightly if this makes placing the rhizomes easier, but otherwise working the soil back between the roots
The rhizome should be placed at soil surface on heavy soils, but a little below the surface on light sandy soils, as they will work their way back to the surface
Replant the divisions in groups, with 30cm between larger plants and 15cm between dwarf plants

Problems:

Those irises divided and re-planted in summer are at risk of drought during dry spells.
Watering the area and allowing it to drain overnight before planting, then watering every five days during dry periods after planting, can help in these conditions

Iris growing tips

Plant them in a sunny spot in late summer. The plants need well-drained soil and at least six hours of sunlight per day. A full day of sun is even better to keep the rhizomes dry.
Give them room to breathe. Bearded iris require good air circulation. Plant them a minimum of 40 to 60cms apart .
Make dividing a habit. Refer to notes above.

Diving Bearded Iris