A trio of flowers of siblings from a cross of P. 'Asa Blue' x begoniifolia. L to R are P. 'Keystone's Barnswallow', P. 'Keystone's Bluebird', and P. Keystone's Whipporwill'. This cross has had amazing variation among the flowers and leaf types produced. When I saw the first seedpods developing on P. rosettifolia three years ago, I was ecstatic! I litterally skipped around like a little girl who's just been given a new pony! Ten years of attempting to get a Petrocosmea flower to produce seeds had finally paid off....now, the question was...."What did I do differently?" Why had it happened this time and not any of the hundred attempts before? Being schooled as a nurse in a nursing program where the model taught me to consider the environmental factors and stressors as factors that impact outcomes, I decided to take a moment and study what factors in the plant's environment were different this time and how were they different. Without boring you with all the details, when I studied this, I came up with two key differences this time....humidity and temperature. After testing those factors for anther year, and documenting my variables and factors...I am convinced that these two factors must be just right for both successful pollination and germination of the seeds to occur.
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The first flower to open in the P. 'Asa Blue' x begoniifolia cross. This flower is quite large, with yellow, purple, and white in the flower. Petals are six in number, with slight ruffling, and white fantasy splashes in the flowers. I want to test this plant and future bloom cycles to make sure these qualities are stable before naming and releasing it, but WOW, what a flower!Humidity is a major factor in successful pollination. I've now tested this several times and have found that unless the flowers being pollinated are grown in very high humidity, such as is found in an enclosed or terrarium-like environment, successful fertilization is rare, and seed production if pods developed, is zero percent! Only once have I gotten seedpods on flowers outside of an enclosed environment, and that time, all three pods were totally empty of seeds. This was also the only time I've gotten a "false" pregnancy with empty seedpods. Inside an enclosure, I am getting approximately 33% success.
Petrocosmea 'Rosemary Platz', my first named Pet hybrid, named for a beautiful lady and a dear friend of mine. The result of that first cross, which was P. rosettifollia x sericea. You can see that the yellow central veining in the leaves of P. rosettifolia was passed along to this hybrid. Flowers look like huge lavendar P. rosettifolia flowers. The plant got it's leaf size and shape and flower color, from P. sericea.
P. 'Keystone's Bantam',(rosettifolia x sericea) named for my friend Paul Kroll's prized bantam chickens, is the sibling of P. 'Rosemary Platz' shown above. This plant is tiny...never exceeding three inches in diameter. From the point that it germinated, this seedling was always very tiny and a bit of a slow grower. Leaves are deep green with yellow veining like P. rosettifolia, and the flowers are very large for the plant size and pure white with light green throats. The little plant blooms very heavily, although it is a strong seasonal bloomer for me. I selected it for it's miniature size and beautiful white flowers. I have used it in one cross with P. forrestii in the hopes of producing miniature Pet hybrids... SO far, the seedlings are all even tinier than 'Keystone's Bantam'. 
P. 'Keystone's Harvest Moon' (rosettifolia x sericea), another remarkable seedling resulting from the first cross. These leaves are not chlorotic...This plant shows an incredible yellow blushing over the entire leaf surface in good light. The yellow veining is also present in the leaves, but the entire center of the leaf is yellow with a dark green margin. LOVELY! Flowers are lavendar and look great above the yellow foliage. It is now in bud and I hope to post some photos of the entire plant in bloom soon. The second factor that seems to play a major role in successful fertilization is temperature...cool temperatures. Although temperature is slightly less a factor, I do believe it plays a role in both fertilization and germination of Pet seeds. My successful crosses have only occured with room temperatures of 45 degrees F or less. Above that, and I have less success, even with flowers that were grown in enclosed environments. In warmer temperatures, fertilization did not occur. As the temperatures dropped, I once again began having success. With regard to germination of seeds, this has been reproduced by several growers and myself now several times. In warm temperatures, germination was poor or failed to occur. When I placed the seed containers in cooler rooms, germination improved significantly and was even "heavy". Experienced growers of gesneriads from seeds have had the same results when I've shared Pet seeds with them.
I continue to study these factors on a daily basis with my Petrocosmea hybridizing program. I attempt to study the effect of temperature and humidity seperately and together. If you have Pets in flower, you must try to make some crosses. It is great fun and there is so much to be learned about this genus and it's culture. Keep notes of everything you do and the factors observed when you do it. Reviewing those notes in the future will likely be amazingingly instructional.
I'll post more on the factors involved in hybridizing Pets in future posts. Stay tuned!
