A Year in the Life: A Tall Bearded Iris in a French Garden

by Sylvain Ruaud

The irises in Les Liliacées (1812) were illustrated by Pierre-Joseph Redouté.

Source: gallica.bnf.fr / Bibliothèque nationale de France

An iris is immortal! At least in theory. Let's say, rather, that it cannot die. It is this faculty that allows us to enjoy an iris in our gardens which was illustrated, described, or selected by Messieurs Redouté, Jacques or Lémon in the 19th century. A predictable process of vegetative propagation gives irises the extraordinary power to clone themselves. Not only can irises live forever, but they also do not age. Irises produced asexually retain all genetic characteristics of the original plant. So, one year in the life of an iris is not much. A healthy iris will live many years and throughout this time it will look very similar except for variations due to weather or tribulations inflicted by humans.

A year in the life of an iris is a perpetual narrative punctuated by the movement of the Earth around the Sun. In France (and other places in the Northern Hemisphere), let’s say the iris year begins in September. This is when temperatures decrease and the iris clump wakes from a period of rest.  It is time for each iris to resume growth and prepare for the future. In our modern irises, those containing I. aphylla genes, the foliage which usually captures energy from the Sun has almost completely dried up. All that remains are short stumps that provide the bare minimum. These leaves will grow a little to facilitate photosynthesis. Just what is needed…a break from fasting. Breakfast!

I. aphylla, a mountain plant, knew not to expose its delicate tissues to frost. The needs of its descendants could be satisfied with a few centimeters of leaf growth. New leaves will remain sheltered within older ones in case of snow. Most new growth will occur below ground and manifests itself by the appearance and development of buds on the sides of the rhizome. These buds are the beginnings of the new plants that will replace irises that lived during the previous season. Assuming sufficient water is available, the combination of rhizome and buds is all that will be required to reproduce identical replacements for a plant that lived the previous year. There is no loss, no degeneration. 

Little by little, the small buds develop into rhizomes. A few weeks after they appear, the round white structures give birth to the three initial shoots at the tip of their tiny rhizomes. These shoots don’t do very much when temperatures are low but enjoy active and vigorous growth when conditions are warm. When the shoots get large enough, three small leaf plumes will spring up from the ground. 

The rhizome is actually a modified stem. As the rhizome grows, lateral plumes become true leaves that frame the central plume. The central plume rises vertically as a cylindrical stem. This stem is also referred to as a bloom stalk; it is solidly anchored to the rhizome in the ground and supports flowers for a new generation. 

Although slow at the beginning, the growth of the iris will suddenly accelerate starting in mid-March (for this latitude). The timing of the growth spurt varies according to the sunshine and the heat of the air, but it is a crucial time in the life of new irises. Plants will not only have to prepare for skyward take-off, but they must also build up flesh in the rhizome. The flesh of the rhizome acts as an energy reserve for the growth spurt that pushes magnificent flowering structures high into the air.  If an open flower is successfully fertilized, then the rhizome must also nourish a seed capsule until it reaches maturity. Necessary materials are drawn not only from the Earth but also from the air around the plant. Leaves must take in a compound necessary for plant metabolism (carbon dioxide) and release a gas produced during photosynthesis (oxygen). Hence it is absolutely necessary that leaves be healthy and well developed. If they are broken or cut, our iris will be weakened.

The stalk that supports tall bearded iris flowers has an exceptionally fast growth rate: roughly 1.5 cm per day! This is the most active period of the year for an iris. To achieve this, the iris draws on energy from the rhizome and water from the soil. Spring rains are essential to transport materials above the foliage and into flowers offering rewards to pollinating insects. When spring arrives a tall bearded iris stem has reached its maximum height: between 75 cm and 1 meter. Although some varieties exceed these dimensions, is not advantageous because of possible damage from wind or rain showers. Neither is lacking in my location. Foul weather may easily knock down a tall iris stem — destroying the efforts of the plant and the hopes of the gardener. 

One may wonder how nature solved the problem of keeping irises upright. Indeed, there is a natural imbalance: most of the load is positioned away from the base, and the rain that falls on the flowers adds weight to the structure. To resist, the iris extends its roots towards the front of the plant. It is like claws that cling to the ground. To perfect this anchorage, the roots differentiate their form based on soil structure. In soft soils, iris roots are long and thin. In rocky soils, they are few but thick. That's why the iris likes stony soils and dreads light soils. In spite of everything, some tall bearded stems fall over. This may be due to genetic weakness in the plant, but the fault is more often due to a lack of water or sunlight. Tall bearded irises require at least half a day of sunlight.

It is now spring, and we are in full-bloom season. The buds open one by one. It is not necessary for many flowers to open at the same time. There are several reasons for this: 1) a staggered opening extends the flowering period for pollinators (and human iris lovers); 2) by opening at the same time, large, showy flowers get in the way of each other; and 3) when many flowers are open, weight at the end of the stalk increases, increasing the risk of falling. Each is something an iris hybridizer examines before selecting a new plant for introduction.  Thus, such imperfections have become rare. 

The big bumblebees, greedy of the nectar of the iris, multiply the landings on the sepals and introduce themselves in the calyx then leave it backwards, carrying their load of pollen towards another flower which they will fertilize…unless a human hybridizer has came along beforehand to dab pollen for a cross of their own. There is a lot of activity in the garden, but it will not last long! The iris season is short...

This brings us to the month of June. Most of the flowers have faded and the plant, which has made an intense effort, enters summer dormancy. With its duty accomplished, the iris forgoes growth processes and instead will focus on keeping existing structures healthy. As temperatures rise throughout the summer,  iris leaves may dry up. Meanwhile, processes underground prepare the plant for the following season. The rhizome slowly reconstitutes its reserves and prepares a new set of buds. Above ground, mysterious work continues within the ovary of the fertilized flower. The watermelon-shaped capsules swell as seeds inside develop. At the beginning of August, seeds approach maturity until one day the capsule containing them bursts open.  The attentive gardener will watch for this event and harvest the seeds he covets before they fall to the ground and scatter. Meanwhile, under the crust of earth warmed by the summer sun, nature completes the development of new rhizomes, those that will be responsible for renewing the initial variety.

The annual cycle is completed. Our iris is ready for the new season...

Growing Irises from Seed

by Tom Waters

We usually propagate irises by division: digging up a large clump, breaking apart the individual rhizomes, and replanting. This method is easy, and because most irises increase rapidly, within a few years you will have plenty of them. This post is about a different way of propagating irises: planting seeds. This is a process that has some challenges, but also has some wonderful rewards. If you've never thought about growing irises from seeds, or have wondered about it but are unsure how to start, read on!

Why?

If you are hybridizing, you will necessarily be growing irises from seed. Hybridizing refers to cross-pollinating irises to produce new varieties. When you cross two different irises, the result is a pod of seeds. Each of the seedlings will grow into a new individual, not exactly like any other iris. Propagating by division only creates exact copies of the original plant, whereas progagation from seed creates only brand new plants, different from either parent. Even if you are not intending to embark on serious hybridizing program to create new varieties to sell commercially, making crosses and raising seedlings can be fun and interesting.

Woohoo! Iris seeds just arrived from Czechia

But hybridizing is not the only reason you might want to raise irises from seed. Some types of irises may just not be obtainable from commercial growers as plants, but you may be able to acquire seeds from a collector or from a seed exchange. This is especially true of iris species, the wild irises from different parts of the world. It can be very difficult to import live plants from other countries, but importing seeds is usually much easier. I've gotten seeds of iris species from collectors in the Czech Republic and from seed exchanges run by the Species Iris Group of North America (SIGNA), the British Iris Society (BIS), the Scottish Rock Garden Club (SRGC), and the North American Rock Garden Society (NARGS). Although the seedlings from a given offering of species seeds will all be different, in subtle or obvious ways, they will all still be plants of that named species, unless the person providing the seed misidentified the plant, or unless it was accidentally cross-pollinated by a different species growing nearby.

Growing irises from seeds also has some other advantages: you get a wide variety of different plants, so you can choose the ones that do best in your climate or whose appearance you prefer. Growing from seed is also a way to eliminate virus infection, should that be a problem.

Finally, growing irises (or any plant) from seeds is a very satisfying experience. It connects you with the whole process of growth, from its very beginning. There's nothing quite like seeing the first bloom of a plant you've grown from seed yourself.

How?

The process of growing irises from seeds is not (usually) very difficult, but it does require patience and attention to factors that you might not have considered if your only experience of raising plants from seeds is growing vegetables or annuals. There have been many articles written on special ways to grow iris seeds; you can find a number of them on the web. In this post, I am not going to suggest one particular method as superior, but just give you an overview of the basics, so that you can get started and learn what works for you.

There are two requirements for germinating iris seeds:

1. They must experience several months of cold temperatures, followed by a warming period.

2. They must have adequate moisture.

Seeds planted into pots sunk in the ground
 (gravel on top protects from washout
and animal interferenece)

The simplest way to meet these two requirements is to plant the seeds outdoors in the autumn or early winter, and let nature take its course--assisting with supplemental water if natural precipitation is insufficient. Seeds can be planted straight in the soil, or in pots sunk into the ground or just left on a porch or in a cold frame. A planting depth of 1 cm or 1/2 inch is suitable for most seeds. Germination usually occurs around the time of iris bloom in the spring.

Some growers prefer to give the seeds their cold treatment ("stratification") indoors, by putting the seeds in baggies with slightly moist vermiculite, perlite, or other sterile medium and refrigerating them for 60 days or more. The advantage of indoor stratification is greater control over the conditions, and the possibility of getting germination a few months earlier. The disadvantage is that you need to be prepared to grow on the seedlings indoors under grow lights for some time, until they are ready to be hardened off and planted outdoors.

Newly sprouted seedlings!

I prefer the outdoor method, as it is less bother and easier to manage with large numbers of seedlings. If I had an extra refrigerator to use for seeds, I might prefer indoor germination.

Whatever method is used to germinate the seeds, they should be transplanted to a semi-permanent seedling bed outdoors when they have at least three leaves. Some may bloom a year later. The year after that, most should bloom and you can decide which ones to keep and which to discard.

The reason the period of cold temperature is needed is that irises, like many perennials from temperate climates, cannot easily survive a winter while still small seedlings. When germination occurs in the spring, rather than in the fall, the young plants have the best possible chance of survival. In contrast, most annuals are fast-growing, opportunistic plants that can grow, flower, and produce seed whenever there is a few months of warm weather.

Dormancy

Even if the requirements above are met, not all the seeds will sprout the first year. With garden variety bearded irises, the percentage will usually be more than 50%, and can approach 100%. Most of the remainder will sprout the following year. At the other extreme, aril irises may sprout a few at a time over a period of 10 years or more. Why is this? It is nature's "insurance policy" against calamities and harsh conditions of various sorts. If all seeds sprouted at the same time, a drought, flood, fire, or other disaster could destroy the whole population. By having the seeds sprout over the course of several years, it is virtually guaranteed that some will survive.

For the gardener, however, such protracted dormancy is a frustration. Few of us want to wait a decade for the seeds we plant to sprout! In irises, dormancy has at least two causes: the hardness of the seed coat, which makes it mechanically difficult for the seedling to emerge, and chemical germination inhibitors inside the seed itself. In nature, the action of water and the cycles of freezing and thawing serve to gradually weaken the seed coat and to leach away the chemical inhibitors.

Some growers have success by planting seed fresh, before it has a chance to dry out. For some types, at least, this can bypass dormancy and result in immediate germination. Of course, one then needs a way to care for the seedlings over winter.

A variety of techniques are used to overcome dormancy artificially. One can attempt to leach out the germination inhibitors by prolonged soaking or use of running water. One can overcome the hard seedcoat by abrasion or chipping (cutting away the seedcoat to expose the embryo). This "forced germination" procedure is often recommended for difficult oncocyclus seeds. The ultimate procedure is to excise the embryo under sterile conditions, and germinate it on a nutrient agar medium. This "embryo culture" can be used to germinate seeds that will not germinate any other way, but it is very demanding work and the young seedlings are very vulnerable.

Whether you choose to use any of these techniques for overcoming dormancy will depend on whether the basic method is giving adequate germination for the types of seeds you grow. I think the best advice is to try natural germination first, and then move on to progressively more invasive and difficult techniques if you need to.

The Payoff

I encourage everyone to trying growing irises from seeds at least once, whether it's making a cross or two in your own garden or ordering a packet of seeds from a seed exchange. It's an adventure, and the first bloom of an iris you've raised from seed yourself makes it all worth the wait!

Here are three seedlings from the same cross, arilbred 'Aztec Prince' (Tasco, 2009) X Iris pumila: