How to Get Irises to Bloom

Plant your irises in a place where they will receive full sunlight. Space your irises so they have room for air circulation. Shaded or crowded plants may not bloom.

Plant rhizomes just under the soil in a place with well-drained soil that is amended with organic matter. Use compost, peat or manure to add nutrients to the soil.

Keep the soil moist from early spring until the end of blooming. Don't allow the soil to dry out or it may stunt flowering. Taper off watering when the blooming ceases as the plant will go into dormancy and too much water can cause root rot.

Test soil with a pH test kit. Bearded irises grow best when the soil is slightly acidic, with a pH between 5.5 and 6.5. Add nutrients to soil if need be. Lower your pH level by adding naturally acidic material such as peat moss or chopped-up pine needles. Raise your pH level by tilling in ground calcitic limestone. Use a low-nitrogen fertilizer when growth begins in the spring and then again when the stem of the flower appears.

Mulch lightly during the blooming season. Do not mulch too close as it promotes rot.

Evaluate the bloom production of longstanding iris plantings. Irises need to be divided every three to five years. If not, they become overcrowded and bloom production decreases. Divide in July or August.

Dig up your iris clumps with a spade. Cut back leaves to one-third of their length. Wash the rhizome with water and then cut them apart with a knife so each division has a group of leaves, roots and a rhizome. Discard any diseased or damaged pieces. Replant these divided rhizomes horizontally, just under the soil, spacing them out to prevent overcrowding.