Reblooming or remontant irises have the potential to deliver their spring show more than once a season, but reblooming depends on the climate and care these varieties receive. According to the Reblooming Iris Society, reblooming irises require the warmer climates found in USDA Plant Hardiness Zones 5 to 9. For a reliable rebloom, these irises also need more water and fertilizer than traditional varieties. Cycle rebloomers have two growth periods that produce new leaves and flowers in spring and fall. A few varieties are all-season bloomers. Most reblooming iris are bearded varieties, although some Japanese iris (Iris ensata) and Siberian iris (Iris siberica) have an extended period of bloom beginning in late spring.
Identify your USDA Plant Hardiness Zone before ordering reblooming irises Some rebloomers have been hybridized to rebloom in USDA Plant Hardiness Zones 8 and warmer. Irises in containers available at local nurseries will usually be rebloomers in your zone.
Choose a site in the full sun. The soil should be well-drained, as bearded irises are prone to rot in saturated soils. Betty Wood of the American Iris Society recommends digging 10 inches into the soil and turning it over.
Add 1/2 bag of compost and 1/2 bag sand for each 3-foot square area and mix in with the soil. Add 5-10-5 fertilizer to the soil according to label instructions. Leave the soil undisturbed for a week. Water the area the day before planting so that the soil is moist but not soggy.
Plant your reblooming irises about 18 inches apart. If your irises are in rhizome form, Betty Wood recommends digging two "trenches" deep enough to accommodate the iris roots and leaving the raised portion intact between the trenches. Place the iris rhizome, which is the thickened part of the roots, on the raised area. If you are planting a containerized iris, dig a hole 4 inches deeper than the bottom of the pot and twice as wide. Take the plant out of the pot.
Backfill with soil and tamp down gently. Cover the iris rhizome with no more than 1/4 inch of soil. Plant the containerized iris at the same soil level it had in the pot.
Water each iris until the soil is moist but not soggy. Renee Shearer of Wild Prairie Farm and Market, a vendor of reblooming irises, recommends giving the newly planted rhizomes extra water to encourage root production. If the weather is dry, water once a week with 1 gallon of water.
Fertilize reblooming irises in early spring and again after flowering with 5-10-5 fertilizer according to label instructions.
Water when the weather has been dry. Soil should not be saturated, but do not let it dry out. Reblooming irises will not rebloom if they are allowed to get too dry.
Remove and kill any iris borers you find on the leaves before they travel down the leaf to feed on the rhizome. Prune only the yellow leaves or leaves with leaf spot. Pruning can disrupt a second round of flowers from forming. You can, however, remove the spent flower stalks down to the base of the plant.
Remove any dried and broken leaves on the ground near your plants before winter. Iris borers often lay their eggs under this debris. Mulch with 3 inches of straw.
Divide reblooming irises when the clumps get crowded, approximately every 3 to 4 years. Water the clump with approximately 2 gallons of water the day before you divide the plant.
Lift the entire clump with a spade.
Locate the "spent" rhizome at the center of the plant. It should break apart easily, according to Renee Shearer. Look for the "increases" which are the newer roots and the rhizomes. Break these sections apart. Use a sharp knife if necessary. These are your divisions. Toss any spent rhizomes.
Cut back the foliage to approximately 6 inches. Give away your divisions or replant them, following the planting instructions in Section 1.