Lovely interaction among plant, hormones and spring (season)

Photo: Nature in Spring (Esetge)

Background:

Have you ever wondered how a plant knows it's time to wake from its winter slumber? Or how all those spring flowering bulbs you planted last fall know it's time to begin that journey upward.

Go Inside:

To understand how this spring phenomenon happens, we have to know what causes the plant to go into dormancy in the first place.

A plant's dormant cycle begins in autumn, when daylight hours shorten and temperatures begin to drop. These key environmental changes cause a bit of hormonal upheaval in the plant, resulting in a slowing to almost a standstill of its metabolism.

Internally during this slowing-down process, the food manufactured and housed in the leaves during active growth relocates to the root zone, converts to starch and is stored for winter. At the same time, physiological changes are occurring inside each cell to keep the plant from freezing. Once all these stages are complete and the temperature remains near freezing for a particular length of time, the plant is said to be dormant.

Each plant species has its own requirement for time spent in the "chill period." Once reached, the plant is ready to stretch its buds.

It's believed that during the fall, a growth inhibitor hormone called ABA builds up in the plant as it goes into dormancy, causing growth to halt. Once the required number of chill hours are reached, ABA begins to break down.

For the bulb planted underground, this is precisely how it knows to begin inching upward. The growth inhibitor is no longer present in a high-enough quantity to stop growth. Ever wonder how a particular perennial could emerge so quickly once the frost leaves the ground? The same principle applies: The growth inhibitor is no longer present.

To complete the breaking of dormancy, as the surrounding soil and air begin to warm, more hormones kick in. These are the growth hormones known as gibberellin (responsible for stem elongation) and cytokinins (responsible for cell division). For all plant material -- bulbs, perennials, trees, shrubs and germinating seeds -- these hormones are crucial for the development of stems, leaves, roots and flowers.

You can fool Mother Nature into thinking spring has sprung.

Many spring-blooming shrubs, such as forsythia, quince, deutzia, honeysuckle, pussy willow, flowering almond, bridal veil spirea and viburnum, can be forced into bloom right now because they only need a relatively few weeks of chilling time. You also can force trees such as flowering crab apples, fruit trees, shadblow and dogwood.

Simply cut a branch and pound the cut end with a hammer before placing it in a bucket of water. This is a trick used by florists to increase the water uptake of woody stemmed plants by breaking the cambium (water vessel) layer.

Acknowledgment: Seattlepie, Britannica