What can we expect from a Petrocosmea when it flowers? How much bloom is the plant capable of? When we look at a Petrocosmea entered in a flower show in bloom, how do we assess if the plant is meeting it's potential for bloom? As an admirer of this fascinating genus, and as both and exhibitor and Master judge for the Gesneriad Society, I am often faced with these questions. When I give a presentation on Petrocosmea, I am often asked how to "make them bloom". So for the past couple of years, I've done a bit of personal research and study on my own plants to assess just what it takes to get the plants to bloom at their full potential. I thought I would share my findings and thoughts with you here.The plant in the photograph above is Petrocosmea grandiflora (or duclouxii, or floribunda...depending upon the source you obtained your plant from...genetically, they are all turning out to be the same species). This plant is my own plant, and the photo was taken this past January, as one all five of my mature plants of this species came into flower. This one is typical of those that I grew in the basement, in rather cold conditions, with humidity between 45 and 70%. The plant is in a 5" pan pot, where it has now been for four years. I have only top dressed the plant with new soil...it has not been repotted in that time. Starting in August, this plant was given plain water, only watered about once a month, and kept rather dry in between these monthly waterings. At times, the soil dried to the point that the leaves wilted a bit. Temperatures in December and January were as low as 35 degrees F and and as high as 52 degrees F. This is it's bloom potential under these conditions. Other plants of this same species, of the same age, in the same potting mix and pot size, that were kept warmer, and given more frequent waterings, (one was wicked on a reservior of dilute fertilizer water) all flowered significantly less than this one. The plant on the reserviour of water had less than half as many flowers, but did have more leaves on the rosette.
So this is what I got with the cold, dry, humid, and no fertilizer treatment described above. Other species given identical treatment all flowered heavily. They are pictured below.....
Petrocosmea minor smooth leaf form was also kept cold, dry and humid. This is the most this plant has ever flowered for me in several years. This species does not appear to flower heavily at one time, but instead seems to flower over a longer period of time, with a few flowers open at one time. This plant is also in a 5" pot and has been there for three years now without repotting.
The above photo is a showplant, a first place winner, grown by the master gesneriad grower Bev Williams of Canada. Her plants are always grown and shown at full potential. The plant is a lavendar flowered from of Petrocosmea rosettifolia. This species always seems to put flowers out along the outer edge of the rosette, rather than clustering the flowers toward the center of the rosette as some species do. Note the flowers here....when entered in bloom, this is what an exhibitor or judge of Petrocosmea should consider in deciding on the points value of "Quantity of Bloom". Many Petrocosmeas entered into shows here in the USA in flower are in my opinion, entered as either immature plants or they have been grown in such a manner that full bloom potential is not acheived. Often Pets in shows have four or five flowers and they score pretty high on the "Quantity of Bloom" section of the score sheet. This is something that judges should begin to consider and "adjust" when the evaluate Petrocosmeas entered in bloom.....again, just my opinion........
A mature but rather small plant of Petrocosmea sp. 'China 2005' in it's third year in a 3 1/2" pot. This plant was also given the cold, dry, humid, plain water treatment described above, and flowered much better this year than ever before. This plant stays much smaller at maturity than other species, so I grow it in a smaller pot. It's bloom potential makes it a great candidate for hybridizing with the goal of producing hybrids with more bloom potential. Cold and dry seems to to the trick with this one too!
A blooming plant of Petrocosmea sp. 'Yumebutai'. I've only had this plant for three years, and it has remained in a 4" pot since I got it...never repotted. When this plant was given to me, the grower said that he'd never been able to flower it. I've also heard this about this species from one other grower. The plant did not flower for me last year, when it was grown warmer and watered more often. But, this year, the cold, dry, and humid treatment worked well. This photo was taken in early February of this year.
SO, what factors worked best for me? Well, the cold is definitely a positive factor in at least increasing the flower count. I've heard from a correspondent in China, who has seen Pets growing in habitat many times, that the plants often experience short periods where they are covered with snow. My basement gets down to the mid-30's F range. Now, I realize that most growers who grow in the living areas of their homes cannot allow the temperatures to get down into the 30's.... but I'm just saying that it definitely helped in my research. Yes, plants in the warmer areas did flower...just not nearly as much as those in the basement where it was cold.
Secondly, plain water helped. The rationale I used for this is that fertilizers might be forcing more foliage growth at the expense of flower buds. Maybe so, or maybe not. But that was a factor in my experiment and those plants did seem to have more flowers and smaller rosettes. I began with the plain water when the plants were beginning to form buds.
Third, high humidity. I feel this helps the buds to mature and not to blast. In the warmer areas, with more heat, the humidity was lower. I occasionally did see a loss of some flower buds in that situation. But, then I advocate high humidity for Petrocosmeas all year long. Why, because my plants with higher humidity look better, grow better, flower better and set seeds better than those with lower humidity. That's good enough for me!
Fourth, infrequent repotting. I won't go so far as to say that Petrocosmeas resent repotting. I've never had a Petrocosmea show any apparent negative effects of repotting. I'm just saying that I don't think it is necessary. I get great results by leaving them along. As long as the mix is draining well and not washed away, my Pets seem very happy staying where they are. Also, I'm not aware of anyone or anything in nature that repots the Petrocosmeas in the mountains of China? Are you?
Last, maturity. By that I mean that I now feel that it takes three or four years of growth for a newly propagated Petrocosmea to reach it's full potential. My plants clearly perform better with each year of life they have...my older Pets perform the best every time! So, again, when considering a show plant....is it mature? This can be difficult to tell since the grower may have kept the plant smaller intentionally, and should therefore not be faulted for choosing to do so. However, bulk seems to improve performance....perhaps the larger root mass and foliar mass support more flower production?
So there you have the results of what I am seeing as I study these plants more closely over the past few years. I hope these observations will help those who are struggling with getting their Pets to bloom......and judges!!!.....consider bloom potential when awarding a Petrocosmea entered in bloom.
