Iris will thrive in most well-drained garden soils. Planting on a slope or in raised beds helps ensure good drainage.
If your soil is heavy, coarse sand or humus may be added to improve drainage.
Gypsum is an excellent soil conditioner that can improve most clay soils.
The ideal pH is 6.8 (slightly acidic), but Iris are tolerant in this regard. To adjust the pH of your soil, lime may be added to acidic soils or sulphur to alkaline soils.
Iris should be planted so the tops of the rhizomes are exposed and the roots are spread out facing downward in the soil. In very light soils or in extremely hot climates, covering the rhizome with 1 inch of soil may be desirable. Firm the soil around each rhizome and then water to help settle the soil. A common mistake is to plant Iris too deeply.
Iris are generally planted 12 to 24 inches apart. Close planting gives an immediate effect, but closely planted Iris will need to be thinned often. Plants spaced further apart will need less frequent thinning.
Newly set plants need moisture to help their root systems become established. Watering depends on your climate and your soil, but deep watering at long intervals is better than more frequent shallow watering. Once established, Iris normally don’t need to be watered except in arid areas. Overwatering is a common error.
Fertilizer depends on your soil type. A light application in the early spring and a second light application about a month after bloom will give good growth and bloom. Avoid using anything high in nitrogen, as nitrogen encourages rot problems.