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Why sleeping plants won't always lie

Posted: Wednesday, January 19, 2000

This week is the perfect model of winter protection for our gardens: Enough cold to send the plants into deep dormancy, then the layer of snow to provide insulation to keep them asleep until spring. We will layer spruce boughs over the garden to help keep it cold so that another warm wave won't bring the new growth poking up too soon.

Dormancy is a peculiar state of being. Plants enter it step by step as the shortening days and dropping temperatures trigger responses that were built into the genetic instructions that each organism carries. These instructions are different for each population, depending on where it grows. For instance, a service berry shrub that grows in Colorado may be of the same species as one that grows on Shelter Island, but it's onset of dormancy will be several weeks later since it has evolved in a place where winter comes later.

The signal to enter dormancy is mostly composed by the gradual lengthening of night. Hormones produced during the dark accumulate in the cell. When they are in sufficient quantity, the cell changes it's mode of operation. The cell walls thicken and the very fluid inside the cell gets thicker. The sugar content rises, acting like anti-freeze, and the rate of respiration - a measure of the speed of life processes - drops.

During the dormant period the plant can tolerate much lower temperatures than it can during the more lively part of it's life, but a ticking clock is running. This internal timer counts off the days of dormancy, and once the preset number of chilling days has been reached, it's ready to grow. The temperature is the next signal, and once the plant is ready even a couple of warm days will start the growth processes again. Our highly variable climate means that plants with timers set for short winters can be called out of dormancy in January during a few short warm days. The all too common result is that February's lower temperatures can kill them, or at least burn off the emerging flower buds.

A very common incidence of this phenomenon is with a bright yellow spring blooming shrub called Forsythia. This is one of the very first plants to bloom each year and people come every summer to our nursery asking for them, saying they don't understand why there aren't any in Juneau. Well there are hundreds of them, but they hardly ever bloom. They have a very short dormancy requirement, and are coaxed out of the protective dormant state during January or February. They get ready to flower, but the next week it's back to freezing and all those flower buds are killed.

Seven or eight years ago spring came early; it warmed up in January and never got cold again. There were Forsythia in bloom all over town, and the most spectacular were those huge old plants that line the space between the Goldbelt building and the downtown fire station. They are 8 feet tall and that year they were a solid golden wall as the long limber branches bent over to touch the ground under the weight of their blooms.

That was the only time I have seen them bloom in almost 20 years. They are nice, tough, pest-free shrubs, growing in their neglected state. They are unnoticed and generally unrecognized, although I know a few people who go every year and cut bouquets to force indoors, since they will burst into bloom in a couple of days in an office. Forsythia are plants that are adapted to another climate, if reproduction is the goal of flowering, that would give them a chance for sex every 20 years or so.

Plants that are growing in places that don't warm up quickly, back by the glacier or in shady corners behind the house, will often stay dormant long enough to be in bloom at a reasonable time, but we don't see them very often. When we are lucky enough to go to a house with one in bloom it is a thrill: There is nothing a lovely as this effervescent golden mass hovering over a bed of dark purple crocus, or paired with the clean white Japanese Quince.

This all leads to the reason we cover our plants once they are dormant. We want them to stay cold and frozen and quiet, we are trying to keep them from coming into growth too soon. It is a good effort, but sometimes they are just like teen-age children - they will come on at their own pace.

David Lendrum is a master gardener and, along with Margaret Tharp, owns Landscape Alaska. Any responses or questions can be sent to www.landscapealaska.com.



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