I looked up planting for you because I thought it would be different because of your colder weather but it's the same:
How to Grow
All the dwarf iris are easy to grow, but to have any hope of healthy plants you need to start with healthy bulbs. As with all bulbs, fat and firm is the rule. Avoid bulbs that are shrivelled and desiccated or soft and squashy.
The ideal growing
conditions are a well-drained soil in either an open, sunny position or under the canopy of deciduous shrubs. This will keep the bulbs dry during the summer, which is essential if they are to spread out into large colonies.
Plant the bulbs about 8cm-10 cm (3in-4in) deep in the autumn. If your soil is heavy and wet the bulbs will either rot in their first year or slowly weaken over a number of years until they fade away. The only way to have lots of flowers
in these conditions is to plant new bulbs each autumn, as you would tulips.