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:

Autumn: Transplanting time for Pacifica Iris

Kathleen Sayce 

September 20, 2015

Many irises are easy to transplant at any time of year. Dig them up, divide, cart to new homes and tuck in. Clip off some leaves to reduce moisture loss while the new roots form, and away they go. Not so for PCIs. Treat them this way, and they go root tips up before you can find your watering can.

Healthy PCI transplants:  new fans, and healthy new white roots. Both of these I. douglasiana pieces are ready to plant. 

There are two times of year to successfully transplant PCIs: Autumn and Spring.

At these times, PCI roots are in active growth. Check the roots, removing soil gently around the base of a fan or two. If there are white roots, one to four inches long, then get out the shovel and start digging. It's time.

New fans on a PCI, but no new roots yet; this plant needs to wait a few weeks before being divided.

Why Autumn and Spring for root growth? Pacifica Iris are native to the West Coast of North America, which has a Mediterranean climate––during the drought period each summer, these and other native species go dormant. In mild winter climates, PCI may have live roots all winter, but they dry down and wait out dry summers.

Summer drought duration depends on latitude, the farther south you are, the longer the duration, which varies from less than three months to more than ten months on the West Coast. I garden at 46°N, so droughts usually last less than three months, though this year it was more than five.

If you water regularly, PCI initiate new roots earlier in the fall than do those depending on rain. You can divide and transplant much earlier in the fall and later in the spring.

This flat of PCI seedlings has been watered regularly all summer, and is ready to move into the garden.

PCI seedlings in pots are tough, and can stand being transplanted several times in the first year or two of life. Even larger plants, one to five gallons, can withstand transplanting slightly outside the Autumn or Spring periods. These have all had regular water, as they must to live in pots.

Other tips:

Mulch after planting to keep roots cool

Amend soil with carbon, such as compost and biochar

Move plants on cool cloudy damp days rather than on hot sunny days

Add 'Superthrive' (a registered vitamin formula for plants) to the watering can

Water well for a few weeks after planting

Use a dilute liquid fertilizer when watering

Every Autumn I host a 'Come and Dig PCI' day in my garden, to share out plants to other gardens in my community. I checked my plants this week; new fans are starting to form, and new roots are short. I'll wait a week or two, until new roots are more than an inch long. 

There are exceptions; one variety has long white roots and could be divided now, but it will tolerate moving in a few weeks. The seedling PCI can be planted anytime from now until early November. They are much tougher than fan sections, which is why growing PCI from seed is so successful for many gardeners. Society for Pacific Coast Native Iris will hold its seed exchange from 1 November to the end of the year, so now is the time to be thinking about what species and hybrids you'd like to grow in your garden from seed. 

New white roots, this PCI is ready for a new home.

For western gardeners, Autumn is the best time to plant many native plants, not just Pacifica Iris. Trees, shrubs, perennials, ferns and grasses all do well if planted now (late September to early November), as the weather cools and moisture arrives from the Pacific Ocean over western North America. This gives the plants a jump on growth for the coming year by establishing good root systems first, with much less water use now and in coming years. 

SIGNA SEED EXCHANGE by Jim Murrain

    Along with James Waddick, I am co-chair of the Species Iris Group of North America (SIGNA) Seed Exchange. Every year we accept, ask, and beg for donations of Iris seeds. While we prefer to get species and species crosses, being a fund raiser, we welcome any Iris seed. Every year we are amazed by the number of rare and unusual Iris seeds that are donated. There are usually a few that are impossible to acquire any way other than by growing from SIGNA seed donations.

    As the seed arrives we make note of the species, cultivar, location, and donor. Once we think all or most have arrived we assign a number to each package of seed. Most packages have far fewer than a hundred seeds, but quite a few have several hundred, while some even have thousands of seeds. We have thought about offering a few kinds by the pound!

    We have seed of all kinds of irises, from bearded and beardless iris, to crested and bulbous, desert and water species, even miniature and giant irises. There is something for every garden.

    Once all packages of seed have numbers we can begin to create a list. I believe several donors must be doctors as their hand writing can be a challenge to decipher. Once the list is complete we send it to SIGNA's editors for publication and to SIGNA's web master to prepare for internet offerings. 

    The next task may sound easy but it is the one I most dread. Printing thousands of labels for the seed packets. Most years we print around six thousand labels! Then we must separate them and pair with the correct package of seeds.

    The entire house is given over to seed counting and re-packaging. A 'spare' bedroom becomes the heart of the operation. Thankfully, members of The Greater Kansas City Iris Society and The Pony Express Iris Society volunteer to help every year. Counting is done in the dining room. Here Ken and Rita Kieff are working diligently away, along with others.

    And in the living room, L to R; Debbie and Scott Hughes, Chuck Robinson, GKCIS President Brian Chadwick-Robinson, and James Waddick. I miss my living room this time of year!

    Finally, boxes of Iris seed ready to send to anxious members of SIGNA. You must be a member of SIGNA to order seeds, but we allow anyone to join at the time of placing an order. Donors will get preference in fulfilling orders as both a thank you and to encourage them to donate again.

    Packets have a minimum of four healthy looking seeds but most have many more. Quite a few have as many seeds as will fit in the glassine envelopes we use. In addition to Iris, there are many seeds of other members of the Iris family such as Geissorhiza, Herbertia, and Moraea. The list will be posted at signa.org later this week if you are interested in seeing the variety available.

    Have you grown irises from seed?  I encourage you to join SIGNA and try growing a wide variety of Iris.