JARS v50n4 - Tips for Beginners: Hybridizing Notes Collecting, Cleaning and Storing Seed

Tips for Beginners: Hybridizing Notes Collecting, Cleaning and Storing Seed
Jim Barlup
Bellevue, Washington

The collection of rhododendron seed pods begins in mid-August and continues throughout the fall. I allow the seed pods to form for a minimum of 100 days after pollination, preferably 120 days, before harvesting. Some plants are very slow to form seed pods, while others, such as 'Nancy Evans' and her offspring, are very quick to form pods. In fact, the seed chambers on 'Nancy Evans' begin to swell in three to four weeks after pollination. Thus I can use it as a test to check pollen viability. If there is no change in the size of the seed chambers within five weeks, I can assume that the pollen used in the cross was sterile and discontinue its use.
Pick the seed pods when they have grown to maturity while they are still in the green or green-brown stage before splitting occurs. The size of the seed pod is not always a reliable indication of maturity. Some plants have small seed pods even when mature. Some plants leave you wondering if they have set seed at all. I collect the pods from these plants as late as possible, hoping for an increase in size.
Working with one cross at a time, I pull the seed pods (eliminating the pedicels) and place them in a container with a tag that shows the cross. (List the parent plant first and the pollen plant second.) I place the pods in 3" tall baby food jars. A 12" x 16" x 4" cardboard box holds from 24 to 30 jars. I stack the boxes on top of each other in opposite directions and keep them at room temperature. The 4" high box allows for air circulation throughout the top of the jars. The jars remain untouched until November or December. (Seed to be sent to the ARS Seed Exchange must be cleaned, labeled and shipped prior to Dec. 1.)

Rhododendron graphic
Drawing by Gary Strong

During the months that I'm waiting for the seed to dry, I have an opportunity to look at the yield for the entire season. Since I generally make more crosses than I want to deal with, I evaluate each cross in terms of the overall picture. As a result of this process, I discard the seed pods for those crosses that have less potential.
After the seed has dried completely, it's ready to be cleaned. My tools consist of pliers for cracking the seed pods open, a tea strainer, 8" x 11" white paper and 2" x 3" coin envelopes. A pair of tweezers or a knife is useful for picking out vagrant chaff. A good, bright light is essential (as well as lots of patience and durable fingers!). To clean the seeds, place the tea strainer on a piece of white paper and work with one cross at a time. Break the pod open in the tea strainer. Some pods can be opened easily with fingers; others are difficult to crack and require the use of pliers. By gently shaking the strainer, the clean seeds drop through to the white paper. Pour the seeds into an envelope and label it with the cross, the year and any other relevant information. It's important to clean the pliers and the strainer and to wipe or replace the paper for each cross in order not to contaminate the seed. Since I harvest over 300 crosses each year, this process keeps me occupied for many rainy evenings. Store the envelopes in a covered plastic container (Tupperware works well) in the refrigerator.
I have had successful germination with seed that has been refrigerated for up to seven years. Seed kept for 10 years didn't germinate at all. Freezing as opposed to refrigerating may increase the life. I read that freezing can cause seed to deteriorate, so I am reluctant to experiment. The seven year time period gives me time to evaluate my crosses. My goals change and seed from crosses made earlier may no longer meet my objectives. With my current focus of using Eastern hybrids, I am in the process of eliminating seed from many of my earlier crosses.
Planting the seed in late December or early January works best for me. You may find that planting earlier will work better for you. But then planting is the subject of another "Hybridizing Notes."
Happy collecting!

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