Section 5: Plant Growth Requirements

Glossary

Lesson 3: Temperature and Climate



 
 Plants grow well within a limited temperature range.
Temperatures that are too high will result in abnormal development and reduced production.
Temperatures too low can do the same, perhaps worse.
However, simple temperature readings do not tell the entire story.
There are climatic conditions that factor into these ideal temperatures to a surprisingly unexpected extent.
Extreme heat or cold can devastate a tree.

 

Temperature factors that figure into plant growth potentials include the following:

 

  • maximum daily temperature

  • minimum daily temperature

  • difference between day and night temperatures

  • average daytime temperature

  • average nighttime temperature


Proximity of water makes for lesser day-night variations in temperature.
Microclimates can also play a role in growing area temperatures.
Changes in elevation, air drainage, exposure, and thermal heat masses can make an area significantly warmer or cooler than the temperatures recorded for the area:
 
 
A 100 metre rise in elevation accounts for approximately 1 degree Celsius drop in temperature.
At night, cool air drains to low spots. Valley floors may be more than 5 degrees Celsius cooler than surrounding areas on hillsides above the valley floor.
Southern exposures absorb more of the sun's heat than northern exposures, causing significant temperature differences. Buildings, fences, and plantings may also protect from (or expose to) cold or warm winds.
Surrounding rock formations or larger bodies of water can form heat sinks that moderate growing conditions in an area. This can lengthen a frost-free growing season by several weeks.

Influence of Cold Temperatures

Plant hardiness is affected not only by low temperatures, but by all of the following factors:

The natural shortening of the length of day slowly increases a plant's cold hardiness.
Some plants are inherently hardier because they come from hardier stock.
A plant can be injured by a temperature lower than its hardening capability.
Gradually lowering temperatures can induce increased cold hardiness.
A plant can be injured due to a rapid drop in temperature with inadequate fall hardening. Similarly, spring frosts, a rapid change from warm to cold, can kill a plant.
Wet, freezing conditions can heave the soil and push out plants, thereby breaking their roots.
Drying winds can cause water to transpire from the needles of a tree, which cannot be replaced from frozen soils.
Sunscalding is caused by the heating of bark on sunny winter days, followed by a rapid temperature drop which ruptures membranes as cells freeze.
Plant nutrient reserves can contribute significantly to a plant's fitness under harsh growing conditions of high altitude or cold winters.


The Crocus Flower

Some flowers are uniquely adapted to withstand harsh winter conditions and seemingly bloom at impossible times.

Many crocuses are cultivated for their flowers appearing in autumn, winter, or spring.
They are native to areas from sea level to alpine tundra in many parts of the world.