Propagation

Louisiana iris growers may never imagine that they want to propagate their plants. Keeping up a garden is plenty of work, but the irises get crowded after several years, and the beds or containers will benefit from dividing the irises and replenishing the soil. And, suddenly, you’re in the propagation business, at least at a modest level.

Rhizome Division

Fall is the best time to divide irises and rework beds to help ensure continued good bloom. It is only a moderate amount of work to dig up a clump and break off mature rhizomes that have not yet produced a bloom. Since fall is the best time to plant bare-root Louisiana irises, the separated rhizomes will have the best chance to become established elsewhere.

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. Separation of a rhizome will work at other times of the year, but special care is advisable in the hotter months. The separated irises should be potted, placed in the shade, and watered well until new growth occurs. Hold the plants until fall before moving to a permanent location, if possible.

Rhizome Cutting

A Louisiana iris rhizome blooms only once. Its offsets will bloom in subsequent years, and the “mother rhizome” will eventually rot. However, the spent rhizome can produce additional offsets that will be identical new plants. The ring-like leaf scars along the rhizome contain “buds” that can potentially develop into a new offset, although the percentage that can be stimulated into producing a new plant is highly variable.

Potted new starts
A recommended process is:

In the fall, at the time of iris replanting, remove the old growing end of a rhizome and cut the remaining portion into approximately 2 ½” sections

Soak for ten minutes in a 10% bleach solution to discourage rot

Plant in pots in a medium of sand and peat or a similar well-draining but moisture-retentive mix

Cover the rhizome pieces with a quarter inch of the planting mix, and make sure that they stay covered

Keep the pot in the shade and moist but not saturated

New offsets will develop on most but not all rhizome sections; success is greater with some varieties than others

When the offsets are at least 4 inches tall, they can be carefully removed, getting all roots and a slice of the rhizome if necessary and potted in good soil. Alternatively, the entire rhizome section can be potted to grow the plantlets to a larger size.

Fertilize periodically with a high nitrogen liquid fertilizer, eventually planting into the garden the following fall.

This process or variations of it can be used at other times of the year and does not have to be applied only to irises that have already bloomed. An iris can be cut a few inches behind the growing tip with that portion replanted. The remainder of the rhizome can be used to propagate more irises by the procedure described. The replanted iris may or may not bloom that year, but cutting it may stimulate the production of additional offsets, a survival mechanism by a damaged plant.

Bloom Stalk Offset

Iris bloom stalks can produce new plants at the lower bloom nodes but not in the numbers that rhizome cuttings can. Rather like daylilies, iris stalks can be stimulated to produce an offset, and this will occasionally occur naturally on a few varieties, especially those with thick stalks. A new plant can be cut off and planted when it appears on a stalk.

Withered flower atop a seed pod.stalk

There are two methods of stimulating the stalks to produce new plants, but unless additional plants are needed beyond those produced by rhizome division or rhizome cutting, they are barely worth the effort.

The first method is to place the flower stalk in a quart bottle of water so that the water line is slightly above the base of a leaf. If placed in semi-shade, offsets may develop in a few weeks. They can be removed when sufficient roots are apparent.

The second method is to place the stalk horizontally in a box with a mixture of sand and peat or some similar medium with the leaf base covered. If kept moist, offsets may be produced, and they can be taken and potted when sufficiently large.

Rhizome separation, rhizome cutting, and stalk offsets are all vegetative propagation methods. The plants produced will be identical to the parent plant.

Seeds

Growing new irises from seeds is the easiest way to develop the largest number of new plants. For hybrids, the limitation is that seeds from hybrid irises will not yield new irises identical to the parents. Sometimes, they will be very similar, but because today’s hybrids were bred from other hybrids with complex backgrounds, their offspring will usually vary markedly. This attribute makes controlled hybridization and careful selection possible, resulting in the many registrations and introductions of new cultivars each year.

Germinated seedlings in pots.
If the objective is the multiplication of the species, such as for a restoration project, growing from seed will help maintain the genetic diversity of those species. It is a much sounder strategy compared to simply cloning the plants. Whether from the work of the bees or a hybridizer, seed pods will begin to swell up in your garden shortly after bloom. It only takes days for the ovary of a pollinated iris to start growing into a seed pod.

Illustration of a seed pod.
If you don’t want to deal with seeds, the best practice is to cut out the entire stalk to within a few inches from the ground as soon as bloom finishes. You will not want seeds to drop in the summer, creating random new irises in your planting. Furthermore, your garden will look much more attractive in the following months with old, possibly yellowing bloom stalks gone, and the irises can use their energy on the new, attractive foliage.

Seeds in a tub.
But if you do want to try your hand at growing irises from seed, here are suggestions:

Stake the bloom stalks with a bamboo stake or the like. As seed pods grow, they often are too heavy for the stalk to remain upright.

Observe the seed pods for signs of yellowing. The seeds mature about 90 days from pollination, but they should be taken and planted when the pod begins to turn yellow or split. If seeds dry out before planting, they may not germinate in the fall, although they might germinate if held for a second year. If seeds do get dry, hydrate them before planting by soaking them in water for a day.

To remove the seeds, lightly score the pod longitudinally along three indentations using a sharp knife and pry open the pod, removing the seed from each of the three chambers. (A box cutter with the blade exposed only a quarter inch works very well).

Actual seed is a small “pellet” contained within the corky covering and consisting of the embryo that develops into the new iris and the endosperm that nourishes it initially. Some hybridizers recommend chipping the corky material at the bottom end to expose the BB-sized seed within. This may increase the germination rate somewhat by allowing water to enter and dilute any natural chemical germination inhibitors.

Plant the seeds from a pod in in a pot with good quality potting soil, cover to ¾ inches depth, and place the pot in a shady location. Keep moist but not soggy. Make sure the seeds remain covered with soil so they do not dry out and insects do not hollow out the seed.

Louisiana iris seeds do not need a cold stratification period to germinate. Germination should begin in the late fall along the Gulf Coast, but the bloom season for the irises is up to two months later in cold climates. This puts seed germination in a period where hard freezes are likely. Short-term dips into the mid-20s F don’t seem to do new sprouts any harm. If colder or longer term below-freezing temperatures are anticipated, seedlings should be protected. Bringing seedlings indoors under gro lights has been very beneficial.

If in doubt about the winter survival prospects for seedlings, seeds can be planted in late winter so that they can germinate safely in the spring.

The pots of seeds and any newly germinated seedlings need protection in the cold North, but not in the lower South.

Seedlings can be bumped up to a larger container or planted into the garden in late winter or early spring. Bloom on most seedlings will occur the following year.

Hybridization

Hybridization involves cross-pollinating irises and growing the resulting seedlings to develop new hybrids and cultivars, not to propagate or increase existing ones. The handling of the seeds is virtually identical to the process described here, but it is proceeded by significant work to decide on the irises to work with and later procedures to evaluate the worthiness of the resulting plants.