Vernalization is a stage in the development of many plants, most notably bulbs, fruit trees, and nut trees. This stage involves exposure to cold temperatures for a set period of time, followed by a period of increased photosensitivity which allows the plant to start producing flowers. There are a number of reasons why vernalization is important to plants, and it is also useful to be aware of when forcing plants to bloom indoors or to bloom earlier than they usually do.
From the point of view of plants, vernalization is an important trait. It alerts the plants to the fact that winter has passed, indicating that it is safe to start producing buds and flowers for the spring. In plants which depend on vernalization as part of their life cycle, the purpose of this stage of development is to encourage flowering at the right time, while also protecting the plant from blooming at the wrong time.
Some plants experience what is known as obligate vernalization, which means that the plant must be exposed to cold temperatures in order to bloom. Others have quantitative vernalization, using cold temperatures as a cue, but not relying on them to time blooming schedules. Plants in temperate zones often experience the quantitative form of this stage of development, using other seasonal cues in addition to changing temperatures to know when it is time to develop blossoms.
One of the issues with vernalization is that if the weather turns warm for a few days or weeks, plants may start flowering too early. The young flowers and buds will be damaged if frost develops. Commercial growers are sometimes forced to prevent this with the use of blowers and heaters over their crops which are designed to prevent frost from setting in and hurting the growing plants. Residents in regions where fruit and nut crops are grown may be familiar with the sight and sound of crop heaters in the early spring when cold spells are predicted.
People can also use vernalization to their advantage. Bulbs, for example, can be tricked into blooming indoors by being chilled for a prolonged period of time and then exposed to warmer temperatures and bright light. Using this technique, gardeners can grow blooms in the middle of December. Vernalization is also important to remember when planting bulbs: many bulbs need to be chilled in the fridge before they are planted so that the vernalization phase of development will occur.
Plants with chilling or freezing requirements are usually clearly labeled with information in garden supply stores, and the various recommendations for specific cultivars are discussed in many gardening books. New gardeners who aren't feeling confident may want to consider taking a gardening class to learn how to get fruit or nut trees off on the right foot before they plant, as the first few years of cultivation are critical to the long-term life of the plant.