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How Plants Know When to Rise and Shine |
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Unusual weather in several regions this winter has many gardeners
concerned about the fate of their perennials; specifically,
whether or not plants, shrubs and trees came out of dormancy and
got zapped by the subsequent return to low temperatures.
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In climates that experience four seasons, crocus
blooms commonly signal the first signs of spring.
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While nobody welcomes the negative effects of abnormal weather,
at the least it shakes us out of our complacency about how nature
works and inspires questions such as, "How do plants know
that winter is coming? What do they do to survive? How do
they know when it's time to wake up in the spring?"
In temperate climates, perennial plants have adapted over the
millennia to survive freezing weather, so what exactly is the
problem? Basically, when water freezes, not only does
it not flow, it also expands. This process is hazardous for
plants because their main component is water. So, when a plant
cell freezes, it does what a frozen water pipe does: it bursts.
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To avoid this situation, perennials follow a to-do list for
shutting down their systems in preparation for the cold. It includes
stopping growth, setting buds for next year, dropping leaves,
moving water from inside cells to spaces in between cells (leaving
within the cells a mixture of sugars and other substances that tolerate
cold without freezing) and storing energy reserves in roots.
To know when to start these preparations, plants rely on environmental
signals such as falling temperatures and/or shortening days. These
conditions trigger changes in plant hormones (for example,
increases in a growth inhibitor called abscisic acid or ABA) that
kick-start the fall to-do list and result in plant dormancy.
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In fall, plants store energy reserves in their roots as they enter a dormancy period for the winter.
In spring, when conditions are right, the plant will utilize those reserves to kick-start growth.
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