How to Plant & Divide Irises
Irises are perennial plants that grow from rhizomes. These structures are thick underground stems from which roots sprout downward and plant stalks shoot upward, breaking through the ground. In the case of irises, rhizomes resemble sweet potatoes. As the plant gets older, its rhizomes multiply underground. Too many of them in one hole cause the iris to decline and stop blooming. For this reason, plan to divide these perennials every three to five years to always have vigorous plants. Separate the rhizomes after the iris flowers, in late summer to early autumn.
Things You’ll Need
- Garden fork
- Garden knife
- Trash can
- Garden scissors
- Spray bottle
- Organic mulch
- Loosen the soil around the iris plant with a garden fork, inserting it under the shallow cluster of rhizomes and pulling the entire plant out. Place it on the soil surface.
- Shake the plant gently and use your fingers to get rid of excess soil around the roots so you see what you’re cutting.
- Take a garden knife and cut the rhizomes growing on the outside of the clump to separate them from the one in the middle. Discard the central rhizome, as it’s the original one that’s now old and has lost its vigor.
- Feel each rhizome in the group with your fingers. If they are firm, retain them. Discard the ones that are soft, like stale root vegetables, or that have discolorations.
- Trim the roots of the healthy rhizomes to 2 inches, and prune any brown foliage. Place the rhizomes in the shade. Mist them with water or cover them with moist paper towels or a moist clean piece of cloth to keep them from drying out.
- Amend the current iris bed by incorporating 2 inches of compost into the soil to a depth of 4 to 6 inches. Or find a new sunny location in your yard for your iris divisions and enrich it with compost. Expand the size of your planting site to accommodate the rhizomes growing next to, not on top of, each other. Perform this step with a shovel and pickax.
- Dig shallow furrows to hold the rhizomes barely below the surface, covered by a thin layer of soil.
- Plant the rhizomes with roots pointing down and foliage above the ground surface. Push topsoil over and around the base of each new plant. Firm the ground with your hands.
- Irrigate your new irises with 1 inch of water immediately after planting the divisions. Continue to give them 1 inch of water weekly until new growth begins.
- Apply a 2- to 3-inch-deep layer of wood chips or pine needles around the base of each iris to choke weeds and slow water evaporation. Replenish the mulch ring as the matter decomposes.