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...