Louisiana Iris Propagation
There are two principal ways to propagate Louisiana irises: by division or cutting from the original rhizome, and by seed. Offsets produced from the original rhizome will produce identical flowers. It is sometimes said that irises will change color over time, but this is not correct. When an unexpected flower appears in a clump, it most likely is due to either other irises "traveling" into it by rhizome growth, to the remnants of a rhizome of another variety previously grown in that spot that has come back and grown large enough to bloom, or to a seed dropping and forming a new hybrid.
Rhizomes can be divided, ideally in the fall. In digging the irises, it is an easy matter to break off the new plants. Since offsets form in the winter or early spring, fall division allows the new plants to grow to sufficient size before being separated from the mother rhizome.
A rhizome will bloom only once. It is the offsets that will flower in subsequent years. The spent rhizome can be used to increase a variety, however. Cut a 2-3 inch section of the rhizome and place it in a medium of sand and vermiculite, sand and peat, commercial potting soil or a similar material. Cover the rhizome section with a quarter inch of the medium and keep moist. It is helpful to have treated the rhizome cuttings by immersing them for about ten minutes in water and bleach (10 percent) to deter any fungus that might cause the cuttings to rot. In most instances, new offsets will form at the leaf scars. When these grow to six inches or more and have formed good roots, they can be carefully removed and planted out. The best practice probably is to simply plant out the rhizome cutting with intact offsets, since the new plants presumably will extract some nutrition from the old rhizome.
Some varieties more readily produce offsets by this method than others. When you examine a spent rhizome, you can sometimes see a small green "eye" along the side that is an emerging offset. Such a rhizome will quickly produce a new plant when treated as described here. In other instances, it may be months before new offsets emerge. Sometimes they never do, and the rhizome section will rot.
Offsets are sometimes produced toward the back end of the rhizome and sometimes near the growing end. Rarely, they will be found toward the bottom of a bloomstalk, much as seen in daylilies.
Growing from seeds produces plants that will vary to a greater or lesser extent from the hybrid parents. Because hybrid Louisiana irises have descended from species that vary widely in color and form, it is difficult to predict what seedlings will look like. This characteristic makes Louisiana irises a fascinating subject for systematic hybridization. Hybridizers make controlled crosses, applying pollen from one cultivar to the flower of another cultivar. Bees randomly do the same work.
Following the bloom season, whether from deliberate cross-pollenization or busy bees, seed pods will become apparent within days or weeks. In Louisiana, these seeds will mature in mid summer. The Fourth of July is an easy target date for taking the seed along the Gulf Coast, both because they generally mature about that time and because of a long weekend. This represents about a 90 day wait from pollenization to mature seeds, so growers elsewhere can adjust accordingly. If a seed pod begins to brown and crack open earlier, however, it should be harvested. Seeds allowed to dry out in the pod may take an additional year to germinate.
The seed pods should be carefully cut open and the seeds planted about 3/4 inch deep in pots of garden soil or potting mix. If the pots are kept moist, the seeds should begin to germinate with the first cool nights in October or November along the Gulf Coast. The seedlings can be planted into the garden in early spring. Most can be expected to bloom the following spring.
Pots of seed can be kept for several years if good germination does not occur in the fall following spring sowing. Some crosses will produce seed that germinates readily and others exhibit delayed or poor germination. After the second year, significant additional germination is unlikely.
It is important to keep the seeds covered with soil or other medium not only to preserve moisture but to prevent the seed from being eaten by insects. The corky coating on seeds may cause them to rise to the surface over time, so additional soil may have to be added to pots.