I am sure most of us know the flowers don’t have scents just to please us gardeners but why? I started pondering this question recently when I noticed that the petunias that I have started from seed (and currently reside in every southern window of my house) have a much more notable scent in the evenings. I have noticed this before; a friend has an orchid that smells delightful in the mornings and like pepper in the evenings, to my nose anyway. Being the science geek and master gardener that I am, I decided to do a bit of research.
Petunias originated in South America and were primarily pollinated by the hawk moth (also known as hummingbird moth) which is more active in the evening. The blossoms actually have an enzyme that regulates this diurnal difference in scent. (Floral Scent Diversity is Differently Expressed in Emitted and Endogenous Components in Petunia axillaris Lines, M. KONDO,1 N. OYAMA-OKUBO,2,* T. ANDO,3 E. MARCHESI,4 and M. NAKAYAMA2) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3292273/ I recommend this reference for anyone that is totally into the chemistry of floral scents, it is on the technical side.
This link is to a fairly short news article about the study and a very interesting quick read, I highly recommend it.
The scents of the flowers play a large roll with the pollinators. Some fruits require repeat visits to be fully pollinated and the scent is one way that the flowers attract and spread the word that they are open for pollination. The pollinator carries the scent and attracts other pollinators back to the flower. One point made is that the scents of the flowers do need to be a part of breeding programs and can help to increase yields. "For watermelon it takes about 12 times to have quality fruit, and it takes 25 pollinations for strawberries to maximize berry size," Dudareva says.
Let me get back to how this started. I have a house full of petunias, violas and alyssum that I have started from seed for an upcoming wedding event. I began all of the work in January and now it is April and cold outside. I had been taking them all out for their daily dose of the “real world” but that has stopped this week with the 2F low we had a few nights ago and snow. But we mountain dwellers know that this too will not last, the temperatures will be all over the place in this month of April, and the flowers will get to go back outside at some point. So in the meantime, I get to enjoy all these great smells that I don’t normally have in April.