Pollinating PCI

All iris flowers have three sets of petal-like structures.

The largest and lowest set is the falls; the falls fold out and down, and are often the most brilliantly colored parts of the flower.

The next set is the style arms; these are smaller, and have a small lip (the stigmatic surface) on the underside, the style, which is part way out the style arm. Style arms are lined up with falls when looking at the flower from above. Small projections, called the style crests or tips, are visible at the top of the style arms. Looking down on the flower, style arms alternate with standards in a ring at the top of the flower, with the falls curving out and down beneath, lined up with the style arms.

The upper set of petals is the standards; these are upright to spreading, seen from the side, and alternate with the style arms when the flower is seen from above.

The stigma or stigmatic surface is a small lip on the underside of the style arm. Pollen attaches to the stigma, then pollen tubes grow down the style arm to each ovule in the ovary. The stigma is slightly sticky when receptive to pollen. It is delicate and easily damaged if rubbed too hard.

The ovary is the slightly swollen area on the stem beneath each flower, often hidden behind the spathes or bracts. After pollination, the petals will dry and drop off, leaving the ovary to grow and ripen seeds.

Pollen forms in anthers. Anthers hug the undersides of the style arms. In nature, bees and other pollinators land on the falls, wiggle under the anthers to reach the nectar at the base of the flower. When they wiggle into a flower, their bodies pick up pollen, and when they wiggle into the next flower, pollen is scraped off on the stigmatic surface of the style lip. As bees visit several flowers on each foraging trip, they carry pollen from prior flowers around to the next, where the pollen is scraped off on the stigmatic lip.

Acting as bees, gardeners mimic this by collecting pollen in small containers and putting it on specific flowers, then removing the falls so that bees cannot also pollinate those flowers. Old film canisters work well to hold pollen; so do clean baby formula jars or other clean small jars.

Pollen should be dry; this is accomplished under wet conditions by using silica crystals to dry the pollen for a few days.

If the day is dry, and the pollen is ready, you can also rub the anther directly and gently over the stigma. It is easy to bruise the stigma and thereby damage it, so be very gentle. If it is damaged, the pollen tube cannot grow down the style arm to the ovary.

Using a small paintbrush, pick up pollen on a clean brush and gently dab it on the stigmatic surface. To ensure that bees cannot also pollinate the plant, gently break off the falls and pull off the anthers from that flower. For more on drying and storing pollen, see articles in back issues of the Almanac.

The stigma is most receptive when the flower first opens. A day or two later, the pollen ripens in the anthers. This way, most iris flowers reduce the amount of self-crossing or selfing, which is where pollen from a flower fertilizes the ovaries of the same flower, and other flowers on the same plant when helped by insects to move the pollen around.

Label both container and lid with the name of the pollen parent, being careful to use one clean container, one lid, and one clean brush for each variety of pollen. To store pollen for more than a few days, see articles in back issues of the Almanac on pollen storage.

After adding pollen to each stigma, remember to label that flower with a water-resistant tag, indicating the date, the pollen parent and the pod parent, or the crossing code. As successive flowers open on one stem, use the same pollen on each flower, or use different pollens, and remember to label each flower with the right pod and pollen parent crossing codes.

Tips

Crossing codes vary among gardeners. Typically, a crossing code uses a letter code for the year and a number code for the cross, such as AB-37, for the second year of crossing (say, 2008), and cross number 37. These codes keep the labels small and short in the garden. Gardeners track deliberate crosses with crossing codes, and keep track of hundreds of crosses per year with this simple method.

The details behind each cross are written out in a notebook, kept dry and safe indoors, including both parents, the date of the cross, the desired traits the cross is meant to enhance, and any other details that the gardener is looking for. These might include plant vigor, number of flowers, a specific flower color, ruffles, or other flower characters. This can also be tracked on a computer.

Remember to keep that notebook or computer file with your crossing notes up to date!

There are two kinds of deliberate crosses to make:

1. Self-crossing or selfing, where pollen from the pod parent is used on its flowers.

2. Out-crossing, where pollen from another plant is used.

Both of these methods produce seed where the parent or parents are known. Bee pollinated flowers, on the other hand, produce open or out crossed seeds where the pollen parent is unknown.

If you are going to do your own hybridizing, it’s important to know both parents. Happy outcomes do occasionally come about from bee pollinations, but then we do not know where those genes came from.

References

Hubley, Robert P., Ghio, Joe, 1981. Planned parenthood, Pacific Coast Native style, SPCNI Almanac, Fall 1981, p 8.

Hujsak, Dorothy and Witt, Jean. 1981. Questions and Answers (on pollination), SPCNI Almanac, Fall 1981, p 9, with an illustration by Jean Witt of iris flower parts.

Lawyer, Lewis. 1988. Expanding our territory, a project open to every member, SPCNI Almanac, Spring 1988, pp 8-23. This issue focuses on improving PCI hardiness and climate tolerance through breeding programs around the world. Contributors include Dorothy Hujack, Jean Witt, Dora Sparrow, Maureen Foster, Bob Ward, Audrey Roe, Clarence Mahan, Elaine Hulbert, Alan McMurtrie, Jo Tunney, Robyn Gulley, Terry Murata, K. Sahin, Maureen Foster, Roy Davidson, Richard Richards, Tomas Tamberg, and Dick Kiyomoto.

Jean Witt Illustration from Fall 1981 Almanac.