If bare-root, plant these kinds of Iris promptly. Never allow them to dry out. Their fibrous roots lack the reservoir of water that fleshy rooted iris have to tide them over dry periods. If potted, do not disturb roots unless plant appears to be pot bound. If that is the case, remove the bottom inch or so of compacted roots and loosen the remaining roots a little.
Although they will tolerate partial shade a sunny position is best. While they do respond well to considerable moisture, well-drained soil will reduce the chances of possible root rot associated with stagnant water. Space them 18 to 30 inches apart as they will form sizeable clumps.
Soil level at planting should be no more than one inch above the crown. Spread roots without crowding and cover with good soil. Humus such as peat moss or compost mixed with the soil produces much huskier plants. Keep well watered. This is especially important for the first year. A mulch of straw, bark chips, or sawdust will suppress weeds and help to keep moisture levels even. Late fall plantings should be heavily mulched to prevent heaving by frost action.
Light fertilizing should be done in spring with 5-10-5, 5-10-10 or a similar formulation. This can be sprinkled on top of the mulch and will gradually be carried to the roots by rain. Do not use lime or bone meal as these iris will do better in slightly acid soil.
If kept well-mulched and never allowed to get too dry Japanese and Siberian Iris will need no spraying. It is a good idea to cut out old flower stems to prevent seed formation. Some people allow the seed pods to form as they are nice to use in dried flower arrangements.
Divide only when bloom declines, openings appear in center of clumps, or additional plants are desired.