Having tried to successfully pollinate Petrocosmea flowers hundreds of times over a period of tens years, it is difficult to describe the joy of being able to say "I'm harvesting Petrocosmea seeds today!" This is my third annual seed harvest and the crosses this year have me excited about the potential for attractive, new foliage and flower characteristics...and maybe even some new colors or at least new "shades" of color. This season, so far, if my counts are accurate, I've applied pollen to 323 flowers. I've collected 21 seedpods so far, all with seeds inside, although some had a precious few seeds. I accuse me of being a bit of a fanatic about Petrocosmeas, I guess. But it is harmless fun and very exciting. I'm learning so much about this genus.
So what am I learning? Here are some observations about hybridizing Petrocosmeas and successful seed set. First, I must say again, that for me, the two key factors in my success, I believe, are making the crosses and allowing the flowers and seedpods to develop in cool temperatures (cold by some definitions) and high humidity....(100% if I can get it). Most of the failures this year, also served to prove this point for me. The early bloom season this year began in summer, when we were quite warm. The plant room was in the mid-70's F. The plants were growing out in the open shelves with the humidity at about 60%. All of those attempts failed. I did get seedpods to form on some P. begoniifolia flowers that were covered, but again they were growing in warm temperatures. All of those seedpods were empty when they ripened. As the plants continued to flower, and the temperatures began to drop with the arrival of autumn, I did not begin to have success until November 29, when I made several crosses in temperatures in the 40's F and most all took! These plants were all enclosed inside my humidity domes, so humidity was 100%. Since then, with the cool temps, I've had nearly 90% success with all species EXCEPT the P. minors...which still refuse to be seedpod parents. I have limited success with this species as a pollen parent and got one more cross this year with P. minor veined leaf form as a pollen parent onto the species P. rosettifolia #3. That was it. Excluding this species, I'm now having excellent results with high success rates if I observe the rules above.
In the photos above and below, you see the seedpod of Petrocosmea rosettifolia #3, which I feel in many ways, is the showiest of all of the forms of this species. The seedpod ripened in 62 days and was FULL of seeds, which can be seen in the second photo below. The seeds are large and plump, so I'm hoping they germinate! This exciting cross using P. rosettifolia as the seedpod parent and P. minor veined leaf form as the pollen parent, was made in the hopes of getting the darker green, and bright yellow veining of the leaves of P. rosettifolia #3 crossed onto the highly glossy, deeply veined leaves of P. minor veined leaf form. Also, I'm hoping that the purple flowers of minor will get some of the deep yellow in the throat of P. rosettifolia #3. I'm also hoping the ease with which P. rosettifolia #3 accepts pollen and sets seed will come through in fertile progeny to be used for further breeding. Who knows what I'll get, but then, therein lies the fun of hybridizing!
A bountiful seed harvest from P. rosettifolia #3. Other forms of this species are reluctant to hybridize or self. This form is almost always successful as a both a pod and pollen parent. Note that the seedpod splits along opposite sides from tip to base. 
The large, showy, snow white petals of P. rosettifolia #3 surround a bright lemon yellow throat. Happily, it is a great parent. Flowers on this form are the largest of any form of P. rosettifolia. 
The mother plant of the seedpods shown above. This photo was taken on the day that I began to make crosses with the plant. I'm hoping that the deep green, yellow veined, and glossy leaves come through in the hybrids. This form also is reluctant to form offsets, whereas other forms of the species form them quite readily. Flowers are large and showy, and present in an attractive fashion over the well-shaped crown of leaves....In many ways, a perfect parent for hybridizing.
The pollen parent of the cross which produced the seedpods above. This is the flower of P. minor veined leaf form..... a fragrant flower! This species has consistently been reluctant to serve as a pod or pollen parent with other Petrocosmeas, or it's siblings, or when selfed. It just doesnt' want to cross. Likely, the problem is that I have not yet discovered some peculiarity about it's fertility. You can bet that I'll keep trying. It has been successful as a pollen parent only twice before....crossed onto P. sericea, P. forrestii, and now P. rosettifolia #3. I'm hoping that the latest cross will infuse some yellow into the clean white throat of this flower for some tricolored flowers in the next generation. If it passes the fragrance along, I'll be happy with that too!!Other things I've learned..... Petrocosmea crosses seem to take a minimum of 60 days for seedpods to ripen. A couple of crosses have taken up to 80 days to ripen. The two top species for successful crosses have been the prolific little P. forresttii in the number one spot, and P. rosettifolia #3 in the number two spot. P. sericea and sp. 'HT-2' would be in the number three spot. All of these have been successful in most all of my attempts to use them as parents. This year, I tried P. parryorum, which bloomed for me with lots of flowers. Not one attempt was successful, and I tried! Believe me I did~~!!! Attempts to use P. parryorum as either pod or pollen parent were all unsuccessful. The pollen was often rotted. I'm wondering now, if perhaps this species does not like the high humidity to pollinate? I'll be trying again next year with plant in both the uncovered and covered areas to see if by lowering humidity I preserve the pollen and maybe have some success? P. kerrii was also unsuccessful, in all but one attempt. Again, little P. forrestii came through for me and produced two tiny seedpods with a few seeds....Now if they will only germinate. P. begoniifolia seems to be the most flamboyant species for producing full, round flowers, with nice ruffling and coloration on the petals. I've used it in several crosses this season in hopes of some breakthroughs in the flowers.
One last observation that I'll mention about hybridizing. Use flowers that have been open for at least four days. It seems to take that long for the pistil to enlongate and the stigma to be mature and receptive. I've gotten to the point that I can tell by looking at the stigma when it is mature. Use pollen from freshly opened flowers, as it seems to lose viability quickly in the high humidity. But, it loses viability much quicker in the low humidity...high humidity rots it, low humidity dehydrates it. I tried storing it in the refrigerator and the freezer...so far, no success using stored pollen.
SO, a fun day, harvesting seeds and getting filled with the anticipation of the new Petrocosmeas to come along as these seeds begin to grow and show their stuff! Stay tuned.......
And you MUST try hybridizing!
