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Big Chill: The Vernalization Process

Winter is coming! Winter is coming!


With spring upon us, nothing better illustrates the season than pregnant flower buds giving way to prolific blooming. These beacons of springtime bloom thanks in part to a process called vernalization.

Vernalization is the exposure of plants to a defined period of cold temperatures in order to enable flower production. This means that some plants, mostly those in temperate areas, require an interval of cold within their life cycle to initiate flowering. The appropriate duration and temperature of this cold period varies between genera.

Every plant that depends on exposure to cold as part of its seasonal workings does so due to a set of genes called VRNs. In the absence of VRN genes, vernalization isn’t needed to initiate a reproductive cycle. Vernalization can take place in perennials, biennials and annuals alike. Familiar perennials that use vernalization to flower include species of phlox, euphorbia, anemone, columbine, coreopsis and lavender.

Vernalization is a critical seasonal cue. Without it, many plants would flower erroneously, meaning instant flower death due to improper environmental conditions and a failed reproductive cycle.

Light also plays a decisive role in blooming. Plants that do not use cold to discern flowering time generally rely on photoperiods instead. The measure of daylight hours compared to hours of darkness induces flowers either by long or short days. Some plants that undergo vernalization will also incorporate photoperiods to calculate seasons.

Vernalization can take place within one season or stretch over two. Perennials will flower, fruit, seed and become dormant for the winter, returning the following year to repeat the process. Biennials, however, will only produce leaves and roots in the first year, then flower, fruit and seed after a winter season. Many of these biennial plants are agricultural staples such as cabbage, broccoli, kale, beets, carrots and winter wheat.

Botany has found its way around this problem, modernizing agriculture and horticulture to how we know it today. Agricultural vernalization has shortened biennial crops to one season by discovering that a partially germinated seed that is chilled for a time will result in productive crops within the same year. In horticulture, understanding temperatures and chill periods particular to plant species means the ability to manipulate seed and flower output throughout a growing season and the cultivation of attractive, flowering plants to send to market.

Vernalization is a critical seasonal cue. Without it, many plants would flower erroneously, meaning instant flower death due to improper environmental conditions and a failed reproductive cycle. Plants have also come to bloom at determined times in order to coincide with pollinators. Blooming on time is crucial to maintaining synchronization with bees, moths, beetles, wasps and other insects. Both seasonality and pollination are most likely responsible for the evolutionary development of vernalization in plants.

Curiously enough, devernalization is also possible. To devernalize a seed, first keep it chilled and then expose it to high temperatures before sowing. This deflects energy to root and leaf development, and is especially useful for vegetable pro-duction, namely onions.

Nature has finely tuned itself over the course of millions of years, thereby delivering the joy of seasons and thus flowering, all part and parcel of vernalization.

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Chilly winds are coming for your flowers!
Last modified on Friday, 21 June 2013 19:57

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