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In winter why do some plants go into dormancy and yet some still produce beautiful often fragrant flowers?

Home / About Ramsgate / News / In winter why do some plants go into dormancy and yet some still produce beautiful often fragrant flowers?

01 February 2019

Gardening in the Winter
Autumn signifies leaf fall in deciduous plants (those that lose their leaves in winter) including evergreens, into a state of dormancy, brought about by temperature fall and light levels. A drop in temperature slows down a plant's metabolism largely because the enzymes that drive these biochemical reactions don't work so well in the cold. Photosynthesis slows, respiration slows and growth stops. Plants are also affected by day length and light levels. This also triggers chemical reactions that induce the abscission layer to close in the axilliary point of the leaf to stem, thus initiating leaf fall.

Plants do almost all the photosynthesis ahead of time when they have leaves, and make enough sugars for the plant cells to survive the winter. The sugar gets stored as starch, plants break this down to use as energy during winter, like a mole uses stored fat when hibernating.

Chilling normally prevents plants beginning growth during warm spells in the middle of the winter. However as climate change kicks in, plants are staying active longer or the time of dormancy is likely delayed or shortened and this could impact on their long term life expectancy due to stress related conditions.

Long prolonged periods of cold can freeze cells in a plant, damage occurs when there is sudden temperature rise causing quick thawing which induces bursting of plant cells, slow thawing largely counters this problem.

If evergreen plants lose all their leaves or the leaves have all gone brown, don't panic, check for green tissue under the outer bark of the stem this signifies healthy tissue. If you are growing more challenging plants in the UK climate, like date plum/kaki (Diospyros kaki) then you may need to give it some added protection during winter.

Some plants will flower on their bare stems during the winter, for example Lonicera fragrantissima, Corylus avellana and Edgeworthia chionantha.

Flowering occurs then, as this gives plants an advantage in relation to maximising pollination potential thus avoiding competition. The native hazel, (Corylus avellana), flowers in winter because it is pollinated via wind borne pollen. Flowering during another period would block the pollen’s potential to fertilise as leaves would form a barrier, limiting pollination. Snow does insulate evergreens from bitter temperatures and the winter sun can dry them out and cause them to burn and go brown. It’s best to leave snow on bows of trees and shrubs unless snow is very heavy and likely to snap the branches. Smaller plants are better left under the snow for insulation.

Haw frost or snow on trees and shrub branches will add to the plants beauty and create a fairyland effect.

All seasons have their beauty. I hope you enjoy and appreciate the winter season too.
Written by:
Kevin Pressland


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