Have we been putting the wrong type of


Author: GUDIN S

Author affiliation: SELECTION MEILLAND, 134 BD F MEILLAND, 06600 ANTIBES, FR.

Published in: Scientia Horticulturae (Amsterdam), volumn 51, pages 139-144, (1992).

Abstract: “Pot plants of Rosa hybrida L. cultivar ‘Meijikatar’ were submitted or not to a 1 month cold treatment just after cut-back. After subsequent culture in a greenhouse, the treatment resulted in an improved production of flowers, hips and seeds resulting either from self- or cross-pollinations. It also determined a specific morphology of the styles and an improved in vitro elongation of the pollen tubes. The cold pre-treatment effect could be explained by its influence on fertility. This influence, although diminishing, could still be demonstrated after pollination on the second flush of flowers.”

I forgot about the quotes in the title bug. The complete title is:

Have we been putting the wrong type of “Bud” in the refrigerator?

Henry, Do you have the complete reference? I’d be interested in knowing what the temperature of the cold treatment was. I’ve got several potted plants of a miniature seedling and this might help it set seed. Wonder how this would affect pollen fertility? This seedling doesn’t produce a lot of pollen either–but it’s got interesting genes.

I’d like to read the complete study as well.

They are referring to vegetative buds. They cut back plants to 3 vegetative buds per cane and just vernalized the plants for a month in a cooler and pulled them out and allowed for regrowth and flowering in a normal greenhouse. They also compared greenhouse grown plants of the same variety cut back the same way and allowed to regrow without chilling and found more flowers and greater fertility from those receiving the chilling. I wrote about this research in an article on repeat flowering in the RHA newsletter a few years ago and suggested that one key point we can get out of this research as breeders is that, if possible, we should be using the first flush of flowers in the spring for breeding. Many exhibitors in warmer areas use the first flowers for shows and then use the next flush of flowers or two for their breeding.

It’s sure interesting that among repeat flowering roses, like this ‘Orange Sunblaze’ that was used for this study, that they are able to place more resources into flowers (number and fertility) early in the season after experiencing winter. This phenomenon seems great for survival since early season flowers should have enough time to mature fruits compared to later season blooms.

What great research indeed.


I found a similar bit of research that started out as a study of the benefits of “split temperatures”, which were intended as a way to reduce heating costs by letting the greenhouse get cooler than usual at night. Instead, the author found a different sort of benefit.

“In general, the number of new breaks, production and quality showed more improvement the lower the temperature regime. This suggested an accumulative effect of low temperature on rose germination.”

Colorado Flower Growers Association Bul. 337 (July 1978)
Split Temperatures and Rejuvenation in Roses
Joe J. Hanan

There has also been some study of “rest”, even without cold. “An Expert” explained how he persuaded the ‘Rose Edouard’ to bloom in flushes and produce finer flowers than usual. He explained, “I will here mention that plants in a tropical climate can obtain rest by withholding water only. A dark, dry, airy building or shed where the sun’s rays cannot penetrate will assist. We must follow nature. In temperate climates cold, frost and snow will give vegetation rest. In the tropics excessive drought, with an arid atmosphere, has a similar effect, which may be seen when the deciduous trees are leafless and the natural indigenous grasses and herbs apparently burnt up, still there is life enough in them when the rains come, which is ample proof of their having been in a state of rest only.”

The Indian Gardener, 1: 266-267 (June 9, 1885)
Rose Edouard
“An Expert”

And another example:

Proc. Soc. Hort. Sci. 7: 33-46 (April, 1911)

Clausen (1959) commented on Cooper’s (1954) experiments with the ‘Wimmera’ ryegrass. Unvernalized Wimmera seed was sown in a heated greenhouse under continuous lighting. It behaved very strangely. Vernalized seed produced plants that were not quite normal, but behaved better under the highly unnatural conditions. Clausen wrote, “The cold treatment apparently starts and equalizes certain gene-controlled processes related to development.”

In other words, even though cold-vernalization was not required for flowering in this cultivated strain, it still stabilized other aspects of development.

It is worth noting that some plants may respond to heat-vernalization, which would occur during summer dormancy.