Winter rest

Winter rest [ Botany - Horticulture ]	Dictionary of botanic terminology - index of names
Synonyms: Winter dormancy, Growth Arrestment, Overwintering, Winter quiescent period, Wintering, Hibernal dormancy, Hibernation.

The quiescent period when a plant naturally stops growing from autumn until spring. Winter rest is a survival strategy which temperate climate species are generally believed to have to survive winters.

In temperate zones as the autumnal temperatures slowly drop and days become shorter ( See: Photoperiod), plant begin to go dormant, sugars are converted to starch for storage in the roots, and cells undergo changes that will allow them to withstand freezing temperatures. If a plant has the genetic potential to do so, when it is dormant, it can survive. The amount and severity of cold that a plant can withstand is a function of its genetic makeup, the type of environment that preceded the plant into dormancy, the amount of environmental protection that the plant , and the severity of the winter. The type of dormancy that a plant can develop also influences hardiness; plants are most hardy when they enter "rest" or true dormancy.

Cactus overwintering:
Almost all cacti need a long cold winter rest with very limited, if any, watering to set flowers.
It is generally accepted that plants kept at too high a temperature or watered too much during the winter rest period will not bloom the following year.
Without this cool winter period (0-10° C) they normally wont get many buds.
The importance of a long cool winter rest where water is completely withheld needs to be highly emphasized with this plants. This are plants which can be at risk for fungal rot even with the slightest amount of water during theirs winter rest. A long winter's rest prepare cacti for the Off-season.

In the wild some species cannot tolerate temperatures below 10 C, other like it best around 5 C and some prefer sleeping under a snow cover.
The overwintering of cold hardy cacti is a process in which them must to dehydrate to survive the cold. They wrinkle up, pulls themselves down into the soil, turn purple and look like death warmed over for the rest period. The worse they look, the better they are doing. Then in spring, they fill back up and look good again.

In cultivation most species like cool night time temperatures around 5° C, although a few degrees under zero during a very short period would not be a problem. But it is not recommend to grow cacti for long periods below zero as this could damage them. Generally in a heated greenhouse no water is given for five-six months between September and April, or between November and March, according to the climate one live in.
Two other important factors to ensure for plant health during overwintering time are sun exposure and a very good ventilation.

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