Starting a Hybridizing Program

It's an exciting time for me, getting back into iris hybridizing again after a long hiatus. Since I have to wait for spring to make crosses, my focus now is on preparation. Here I share some of my preparation activities, in the hopes that others starting a breeding program will find this of interest.

Setting Goals

Some people like to plan all their activities in detail ahead of time, others prefer to be spontaneous, trusting that they'll know where they're going when they get there. Some hybridizers start out with a very specific goal, perhaps even a mental image of an iris they hope to create. At the other extreme are those who go into the garden and decide what to cross on impulse. I fall in between, but more toward the advance planning end of the spectrum. For myself, it is important to have some notion of what sorts of crosses I intend to make, as this affects what plants I acquire, and whether or not to save pollen from early blooming plants. On the other hand, I say "what sorts of crosses" in a quite broad sense. I think of types of irises (e. g., tetraploid arils) and then keep on the lookout for particular varieties that fit the bill.

My original inspiration in hybridizing is to create fertile arilbred dwarfs and medians. I've always had a special interest in the smaller arilbreds. I'm intrigued by the way dwarf and aril characteristics combine, I love their charm as garden plants, and I would love to see many more of them. It seems that great progress could be made with arilbred medians if only we had fertile families of them to work with. The two possibilities are the families that would result from breeding I. pumila with tetraploid arils and 48-chromosome dwarfs and medians with tetraploid arils. There are only a scant few examples of these two families at present, so the goal of fertile small arilbreds implies building up these two families from wide crosses between the parent groups. This brings another goal into view, as the tetraploid arils presently available are mostly Regelias and RCs with strong Regelia characteristics. To get a wider range of types for my arilbred medians, it makes sense to also work on expanding the tetraploid aril family. Likewise, the 48-chromosome medians today are based almost entirely on I. aphylla, and it seems a good idea to expand the base by using other species, particularly the smallest ones.

So in this way, one goal implies several supporting goals. The supporting goals are also valuable objectives in their own right: new tetraploid arils could be used in many ways, not just for breeding arilbred dwarfs and medians.

With this outline in mind of what I want to do, it becomes possible to identify which varieties will be helpful as parents, and to take advantage of opportunities to acquire less common varieties.

Preparing the Garden

I was fortunate in that I was already putting a lot of work into preparing flower beds before deciding to start hybridizing again. We have a new home on basically undeveloped land, so it was a goal from the beginning to transform the backyard (at least the parts near the house) into an attractive, enjoyable outdoor space. So when my irises started arriving in August 2010, everything was ready for them.

The challenge will be to keep ahead of things in future years, as I not only acquire new plants but (I hope!) have to accommodate a substantial number of seedlings. I put in some time most weekends breaking new ground somewhere on the property. Not all will be used for irises (I promise, really), but it's a good discipline to keep bringing new areas into cultivation and managing the growth of the weeds.

I'm a great believer in the importance of soil preparation. I use lots of organic matter, and dig with a shovel rather than a tiller. I've found from past experience that it's a big mistake to plant in ground that has not been properly prepared. Although it's tempting to think that the 'hybridizing garden' can be out somewhere in the back forty and receive less attention than the places visitors are likely to see, the plants I'm hybridizing with also need to be growing and blooming their best to ensure their survival and good seed production and seedling growth.

Acquiring the Plants

I find I take quite a different attitude when acquiring plants for the breeding program than I do when just adding to my iris collection. If I'm buying an iris just to enjoy it in the garden, I will usually order just one and wait a few years for it to grow into a nice clump. If I intend to breed with an iris, however, I will usually order three. This serves as insurance in case one doesn't survive, and it also gives (potentially) more blooms to cross with the first spring. It essentially saves a year. In a hybridizing program, time is an important asset - important enough to trump some concerns about expense or garden space. Exceptions to this "buy three" philosophy are society plant sales and growers that list an iris as being in short supply. In these cases, I feel it's best to give as many people as possible the opportunity to grow the iris.

Because I have chosen to work with species and other irises that are not very widely grown, I'm quite sensitive to the need to take advantage of opportunities to acquire the rarer ones. I don't take it for granted that they will be available whenever I want them. So I spend a fair amount of time looking around on the web for sources of the irises I'm interested in, often going outside the usual iris specialists. I'd rather overextend myself in acquisitions a bit early on than spend years regretting not having an iris I could have obtained but didn't.

I've also joined the AIS, ASI, and SIGNA, and their online discussion groups. It's good to learn what others have tried, what they are growing, and what they've learned in their own efforts to acquire and grow the irises I'm interested in.

Additionally, I'm making it a practice to acquire the top Award of Merit winner in each bearded and arilbred class each year. This serves a two-fold purpose: keeping me acquainted with the current standards and expectations for each class, and providing potential breeding material of modern vintage.

Species from Seed

Why grow iris species from seed? It will likely be three years or more until they bloom, compared with one year for a plant, and open-pollinated seeds from a garden may not come true. A few reasons are obvious: seeds are usually less expensive, and you may not be able to find a source of plants for a species that is available as seeds. There are some other important reasons, too, that may not be so readily apparent. First and foremost, seeds give you the opportunity of raising a small population of the species, not just a single clone. If you are planning to use the species extensively in breeding, this genetic diversity is an important resource. It increases the possible different traits the seedlings may show, and ensures that genetic weaknesses do not become ingrained into your breeding lines. Furthermore, the diversity provides an opportunity for selecting forms that are best suited to your own climate. This touches on yet another advantage: irises raised from seeds are automatically acclimated to your own garden conditions, which can increase the odds of success.

Finally, each iris grown from seed represents a "fresh start", free from virus or any other malady a long-lived clone may have acquired over the years. Periodically rejuvenating your species populations from seed ensures vigorous stock in the long run.

Alpine and rare plant specialists often offer seeds for sale, as do rock garden societies, SIGNA, ASI, and MIS.

Having come to iris breeding from the world of vegetatively propagated named varieties, it can be easy to think of a species as just another cultivar to use in breeding. I'm trying to adjust my mindset to a more ecologically informed point of view, in which species are populations of plants with varied genes, periodically renewed and adapting.

Keeping Records

Yes, it may sound very geeky, but I enjoy planning how I will keep records of my hybridizing. I worked out a system of seedling numbers, and made a spreadsheet for tracking things like pollination success rates, seed germination rates, and so on. I also have a pretty good idea of what I'll be jotting in a notebook as I'm outside making crosses. Some of this preparation is probably a result of my wanting something to do before the irises are actually in bloom, but I like to think it will help everything work more smoothly next spring and in future years.

Seedling Numbers

Every hybridizer seems to have their own system for numbering crosses and seedlings. Since I am interested in working within several fertile families, I came up with a system that identifies the family, then assigns each cross within a family a serial number, and finally assigns each selected seedling its own serial number:


n is a letter representing the family (A=AAAA, B=AATT, P=PPPP, Q=AAPP, S=PPTT, T=TTTT), xxx is the cross number, and yy is the seedling number. If the cross is diploid, a lower case letter is used for n. Crosses between families use two letters. Thus SDB x AB = SB.

I opted not to use dates in my seedling numbers because I may be making the same cross in several different years, and because I expect protracted seed germination, especially of the aril seedlings, to render the cross year relatively unimportant.

Fertility and Germination Data

I track the fertility of the different irises and crosses, and the germination rates of resulting seed. Therefore, the spreadsheet has a place for the number of pollinations made for each cross, the number of pods formed, the number of seeds produced, and the number of seedlings sprouted after 1, 2, 3, and 4 years. The spreadsheet automatically calculates percentages as the data is entered.

Pedigree Research

For some of the irises I intend to use in breeding, I have researched pedigrees using the online Iris Encyclopedia at the AIS website. Although the online encyclopedia is not yet as comprehensive as the printed Registration and Introduction volumes, it has enough information to go back many generations in most cases. Although this is an interesting exercise, I think most of the value comes from researching the first three or four generations at most. I think there is something to be gained in learning whether irises you are crossing derive ultimately from the same breeding lines (such as the Fay/Hall pinks, the Cook amoenas, or the Hager aphylla line).

The Hybridizing KitIris hybridizing kit

I've assembled a modest collection of paraphenalia for hybridizing. I use gelatin capsules for storing pollen (size 0 for small anthers and 00 for larger ones). The capsules are kept in a peanut butter jar with packets of desiccant to keep the pollen dry. I will also be trying glassine envelopes for pollen, as it seems these may be less airtight and help in keeping the pollen dry. (Update: I now use the envelopes exclusively.) The jar is kept in the fridge during bloom season, and then transferred to the freezer to store pollen of late bloomers for use the following spring. Pollen should be dry before closing the capsules. Old Altoid tins hold the capsules or envelopes when I'm using them in the garden.

Tweezers are for plucking the anthers from the blooms. Many people prefer the reverse-action kind that stay closed unless you squeeze them, but I prefer the simpler ones, which are more intuitive to me. I have brushes to apply pollen, and alcohol to clean the brushes between pollinations. I've been mostly using toothpicks rather than brushes, which have the advantage of not requiring the cleaning. I do use brushes when pollen is scarce and I need a little more control.

Price tags are used to label the crossed bloomstalks in the gardem, although this is not usually necessary since I usually put the same pollen on every bloom of a clump. The notebook is for recording the crosses: cross number, parentage, dates, number of blooms pollinated, and any other pertinent notes, such as which stalks in a clump were used, if not all stalks were used for the same cross. The notebook records are transferred to computer files (spreadsheets) for permanence. Recently, Iive been forgoing the notebook entirely and entering information directly into the computer wehn I come in from the garden. And finally, of course, there is a box to tote all this stuff out to the garden!


 Tom Waters

September 2010

updated February 2019

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Unless otherwise noted, all text and illustrations copyright Tom Waters and all photographs copyright Tom or Karen Waters. Please do not reproduce without permission.