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:

Winter Iris Gardening

by Tom Waters

This being the day after Christmas, it seemed appropriate to write something "seasonal" for this blog post. So what does winter mean for the iris grower?

A word to the wise: Iris growers live in many, many different climates. What is true in one climate may be false in another. Be suspicious of any gardening advice on such topics as winter care that is written as though it applies everywhere. In this post, I'll mention a few things that one might want to consider, but I do not offer any absolute advice. For that, you need to speak with other gardeners in your own area or just do some trial-and-error work on your own.

All irises grow in temperate climates. They are adapted to the changing seasons. Most kinds have periods of rapid growth in spring and autumn, but slow down or go dormant in summer and winter. In fact, irises need a distinct winter with cold temperatures in order to bloom; they will not do well in tropical climates.

Selecting irises for your winter conditions. All garden irises are ultimately derived from wild iris species from different parts of the northern hemisphere. The climate where those species live can tell you something about how those irises will do in various climates. Louisiana irises, for example, are native to the southeastern US, where winters are mild and summers are warm and wet.

Among the bearded irises, winter hardiness varies a great deal. The original diploid tall bearded irises come from the species Iris pallida and Iris variegata, native to central Europe, often at rather high altitudes. They have little difficulty surviving cold winters. These diploid types are today mostly found among the miniature tall bearded (MTB) irises. Modern tetraploid tall bearded irises also have species from the eastern Mediterranean in their ancestry, meaning that some of them fare poorly in colder climates. Depending on the particular mix of genes, modern TBs can be utterly hardy or quite tender, or anything in between. So how is one to know? Checking with other growers in your own area is always good advice, but one can also take a clue from the region where the iris was originally hybridized. Irises bred in Canada or in the US midwest are almost certain to be suited to cold winters, while those from the Pacific coast are not necessarily so. Border bearded irises (BBs) have the same ancestry as TBs, and so the same considerations apply.

Among the dwarf and median classes, miniature dwarfs (MDBs), standard dwarfs (SDBs), and intermediates (IBs) virtually all have Iris pumila in their ancestry. This tiny species is a native of central and eastern Europe, growing at higher elevations and in more continental climates than most of the TB species. It is very hardy, perhaps to a fault, because it has a reputation for failing to grow and bloom well in climates with mild winters. Consequently, growers in places like southern California and Arizona sometimes find that these types (the MDBs especially) do not do well for them.

Arilbreds vary in their degree of winter hardiness. The aril species grow in southwestern and central Asia. Although some of these are adapted to the very warm climate of the deserts of Israel, Jordan, and Syria, most arils are in fact mountain plants used to extreme winter cold and extreme summer heat. So why do northern growers find many arilbreds too tender for their climates? The fault is probably in their TB ancestry. The center of early arilbred breeding was Southern California, and the TBs used in arilbred breeding were those that did well in that mild-winter climate.

Having made these generalizations, I encourage iris growers to experiment with types that "conventional wisdom" might recommend against. Every garden has microclimates, and every category of irises has cultivars that are surprisingly adaptable.

Winter care: mulching. Irises are not very different in their needs from other perennials you may grow, so in climates where winter mulch is beneficial, it can be applied to iris plantings as well. The main purpose of a winter mulch is not to keep the plants warm, but to moderate the cycles of alternate freezing and thawing that can push plants out of the ground expose them to risk of winter rot. Snow makes an excellent insulator. If your climate is such that you can count on a fairly thick cover of snow all winter long, you have the ideal natural winter mulch!

I am not so fortunate here in northern New Mexico. We get temperatures below 0 degrees Fahrenheit every winter, most often without any snow cover at all. I do not apply a heavy much, but I do allow garden debris to stay in place over winter, giving the crowns of the plants some buffer against the wind and cold. I also put down a layer of cotton bur compost in the late autumn. Winter weather gradually degrades it and incorporates it into the soil, but in the meanwhile it seems to offer a little protection.

Beware that mulches can harbor overwintering insect pests and can collect water. In climates where these are issues of concern, it is best to forgo mulch.

Winter care: water. In climates where the ground freezes, watering in winter is nor desirable, and often not even possible, so winter offers relief from this particular garden duty. Many gardening books seem to assume this is true everywhere. However, if you live in a dry climate with spells of warm weather during the winter, you should pay attention and provide a little supplemental water as needed to keep the garden from becoming totally desiccated. Not much is needed: remember that the plants are dormant or semi-dormant, and that evaporation is less because of the cool temperatures.

Seeds! For those of us who like to grow irises from seeds, winter is an important time. Like most temperate perennials, irises have seeds that resist germination during the winter, to sprout when spring arrives. The cold and wet of winter are actually part of the preparation they need to germinate. The simplest way to grow irises from seeds is to plant them outdoors in the autumn, where they can overwinter and come up the following spring. Nature is unpredictable, of course, so many people prefer to use an indoor refrigeration process to replicate winter conditions. I'm not really set up for that kind of project, so I plant mine outdoors and let nature do her work.

Seeds from my own crosses get planted around the time of the first frost in autumn. Those I get from seed exchanges or other providers usually come later, in December or January. The longer they have to experience the winter wet and cold, the better. Since winter and spring weather here is erratic, germination is unpredictable. I generally leave the seeds in place for several years.

I hope I've touched on at least a few topics of interest. What are your own experiences of irises and winter?

Reblooming Iris Program: Zone 6: On the Cheap

by Betty Wilkerson

Many of the improvements in irises have been made by the backyard gardener, and some of their creations have won The Dykes Medal. You can spend a small fortune, hunting up fancy tweezers and paint brushes, but it's possible to breed irises without all this. When I started my rebloom program, I had a child in elementary school, and two in high school, so I couldn't justify spending much money on the iris program. I bought a cheap iris colletion from Schreiners and the next year I ran across a really cheap fall blooming iris collection from Fields, a mail order catalog. Then, I bought a few rebloomers from Monty Byers. 

An empty milk jug, cut into strips, and then cut again, made good tags.  I punched holes in one corner, with a hole punch, and used some orange yarn from my crochet bag to make ties. They were neat, but the birds really liked them, too, and used several in building their spring nests. If one was missing, I learned to look to the tree tops.  The tags would glisten and reflect sunshine from up in the trees. After I moved to Allen county in 2003, I switched to strips of plastic venetian blinds shown below.  To prevent fading, I use paint markers. I made 150 tags so I would not have to reuse any during any season. Early on, I bought a couple of pair of tweezers from Wal-Mart. I stressed over the method of pollen transfer until I found I was comfortable with using my ring finger as the implement of transfer.  Works fine for me.

A few years back, I bought a large garden bag that will hold all of my hybridizing equipment, and then some. Before the new bag, I would put everything in a gallon size ziplock bag.  The new bag is lined with pockets on the inside, which is convenient for pollen envelopes, tweezers, seed packets, nozzles for the hose, etc.. It even has a clip for my keys, if I choose to use it.  

Garden Bag

Hybridizing Tags

Lace Bonnets

The first summer I was in Allen County, 2004, a pod went missing.  It was my favorite from 'Strictly Ballroom' X 'Mariposa Skies.' Sorry, I do not have pictures of the irises. I spent way too much time looking for the pod, but with absolutely no luck. The following winter I made a bunch of these lace bonnets to protect my pods from the deer.  Haven't lost a pod since 2004.

Personal Size Envelopes
for Seed

Once the seed are harvested from the pods they are usually wet or at least damp and they need a home until time to plant.  Rather than take chances of getting the seed mixed up, it's just easier to go straight to the envelopes.  I put all of the permanent information onto the envelope, pod parent, pollen parent, and seed count, then I put the seed into the envelopes.  I place it/them on an envelope rack to dry.  I shake the envelope each day and turn it upside down. This is to make sure all seed fall to the other side.  They are usually dry within a week and can rest until planting time at the end of Oct.  The soil must be cool.

Mum Pots for Germination

Chicken Wire

Soil should be placed in the pots about six weeks before the seed are planted.  A natural settling of the soil in the pots will leave air in the soil, important, where tamping does not. In my zone 6 garden it's important to put chicken wire (mine is plastic and reusable) over the pots to keep out the vermin.  In my zone 6 garden the average date to expect sprouts is April 1.

Landscape Fabric

As I've grown older and more crippled, I've adjusted the way I care for my iris. The cost of my operation went up at the same time.  DeWitt woven landscape fabric is really good.  I buy it in big rolls that will cover about five beds.  I like the stuff with the green lines because it helps make straight rows and I need all the help I can get.  Each spring I must check for crowding and cut the landscape fabric where needed.  I use a thick grade of black plastic for the paths. I use a piece of pvc pipe with paint markers every six inches to measure between plants.

If you want to make some iris crosses, but don't think you can afford the equipment?  Please give it another thought.  Be creative. We need reblooming hybridizers in the middle and cooler states, zones 4-6.  To get rebloom you will need to use really strong rebloom stock. I'm always willing to discuss anything iris!  Just find me on Facebook or e-mail me at bridgeintime@aol.com. Put "irises" in the subject line. Good luck.