JARS v50n3 - Tips for Beginners: Hybridizing Notes, Part II

Tips for Beginners: Hybridizing Notes, Part II
Jim Barlup
Bellevue, Washington

In "My Way of Hybridizing - Part 1" (Spring 1996 issue), I ended with making a cross of Rhododendron 'Nancy Evans' and R. 'Mrs. Furnival'. I used a truss from 'Mrs. Furnival' that produced a reasonable amount of pollen as the pollen parent. Generally, plants have a similar amount of pollen in each of their trusses. However, there are plants with no pollen at all, while others will have pollen in only some of the trusses of which 'Mrs. Furnival' and 'Lem's Cameo' are examples. One truss may have no pollen and another one on the same plant may be dripping with pollen. Searching for pollen can be frustrating, but don't give up until you are sure that none of the trusses is hiding it. I've been known to check gardens other than my own for elusive pollen. Please ask for permission before you take pollen from someone else's plants.
After you harvest the pollen, you may want to store it for use next week, next month, or even next year. One-inch No. 00 gelatin capsules work well for storage. Place the stamens with the anthers first in the capsule and cut off the stems that extend beyond the end. Label the capsule with the name of the pollen parent. I use a color code to indicate the year collected. If it is valuable pollen, you may want to fill five or six capsules. Fill the capsules about one-half full and place them, uncovered, in a dry place until the stamens are dry, usually three to four days. Then close the capsules and store them in the refrigerator until needed. Freeze the pollen that will be sent to the Pollen Exchange and the pollen that won't be used until the following season. When you are ready to hybridize, remove several of the stamens and tap them on the side of your hand to release the pollen. You may need just one or two stamens or you may use half of your supply for one pollination. Return the capsule to the refrigerator when done. This year I received pollen capsules from an Eastern hybridizer that contained only the anthers. This was a new method for me, but I understand that it is the accepted method for the Pollen Exchange. The Western hybridizers with whom I exchange pollen store the pollen with the stamens intact. The apparent reason for storing anthers only is to reduce the risk of fungus. I have never had a problem with fungus. My challenge is to cover the capsules before the stamens become brittle. When hybridizing with anthers only, I use tweezers or a camel hairbrush to place the pollen on the stigma.
I'm thinking ahead to next spring. I want to cross 'Independence Day', a larger sized July bloomer, with ( R. yakushimanum x 'Lem's Cameo'), a smaller sized May bloomer. I want to use the smaller plant as the seed parent to increase the chances of creating a smaller, late blooming plant. This means I will have to have 'Independence Day' pollen available in May. I collect the pollen in July, dry it and place it in the freezer. At the end of the hybridizing season I freeze all the pollen for next year's hybridizing. My collection may number from 50 to 80 varieties. I store the capsules in a quart mason jar. Fill the jar one-third full of silica gel and place a pad of cotton over the gel. Then fill the jar with capsules. Cover tightly and place in the freezer until you're ready to start hybridizing again. At this time, transfer the capsules from the jar to a bowl in the refrigerator. Newly collected pollen goes in the same bowl with its respective color code. I've had some pollen last for three years, while other pollen loses potency before the end of the first season.

rhododendron graphic
Drawing by Gary Strong

Many experiments are necessary to learn which rhododendrons have viable pollen and which plants do not. 'One Thousand Butterflies' is sterile as a seed parent, but its pollen is viable, whereas 'Nancy Evans' is just the reverse (it can be used as a seed parent but not a pollen parent). The majority of plants will work both ways and can be used as the pollen parent or the seed parent. If you have selected two plants to cross and you aren't sure about their fertility, test them by using each plant as a seed parent and as a pollen parent. At least half my crosses are experimental. An example of my experimentation is a need to know if a particular cross has any plants with viable pollen. ('Nancy Evans' x 'Mrs. Furnival') would normally produce plants with sterile pollen since 'Nancy Evans' pollen is sterile. Are all the offspring going to be sterile? The only way to know is to try every plant of this cross. Of 16 plants that bloomed, four did not have pollen and 12 did. I used pollen from all 12 of these plants on seed parents that are known to set seed easily. One of these 12 crosses has viable pollen. The chain of sterile pollen plants was broken. The resulting offspring from that plant can produce more plants with viable pollen.
Since I have been speaking of the cross ('Nancy Evans' x 'Mrs. Furnival'), let me explain the progression. The first cross produced three keepers, a pink, a white, and a small flowered yellow. They are adequate but not wonderful. The second cross produced some beautiful bi-colors, some excellent deep yellows with red to brown blotches and one exceptional pink. I have three more plants from this cross that have yet to bloom. (It's things like this that make hybridizing so exciting!) These plants are so good that I decided to plant the seed from the third cross. I used only one plant of 'Nancy Evans' but three different plants of 'Mrs. Furnival'. I am curious to see what color line the new cross will produce.
Be persistent with a plant you're using for hybridizing until you know it won't work. This could take a few years of experimentation. Plants such as 'Gomer Waterer' and 'Taurus' can be almost impossible either as a pollen parent or as a seed parent, but that doesn't mean it can't be done. You may find a way. I remember someone saying that the only way he got any pollen out of 'Anna' was to place a truss in the back window of his car in full sun. That would shake a truss up! I used pollen from ('Nancy Evans' x ['Whopper'* x 'Lem's Cameo']) for crossing with many different plants for two years. Not one cross took. Cuttings of this plant bloomed in three years. I had to try it again. Much to my surprise the pollen was viable and took on every plant I put it on. I don't understand why this reversal occurred, but I'm grateful. If you have a goal in mind, don't give up. You may find a way. Have a successful hybridizing season.

* Name is not registered.

Jim Barlup is a member of the Cascade Chapter and the hybridizer of 'Fire Rim', which received an ARS Conditional Award in 1995.