Section 5: Plant Growth Requirements

Glossary

Lesson 1: Water Requirements



©iStock


Like all other plants, these flowering cacti are made up mainly of water.
Yet they consume very little water.
How can this be?

Answer: They lose very little water because they have a very low rate of transpiration.

Plants are over 90% water, so it's no wonder that they require water for their growth and sustenance.
But different plants have widely differing water needs depending on a variety of factors, such as the following:
Green leaf plants, that bear fruit, require more water than succulents. For example, tomatoes require more water than cacti.
High temperatures are usually accompanied by higher transpiration rates, meaning the plant will need to take in more water. Prevailing winds have the same effect, again because they cause higher transpiration rates in plants subjected to them. This is true even for succulent plants.
Sandy soils can dry out very quickly. Heavy clay soils retain moisture for a much longer period of time. Also, some soils contain more organic matter, which also facilitates moisture retention. Plants growing in different soils must we watered accordingly.


There is no rule of thumb for how much water
a plant needs that can possibly apply to the
myriad of plant types on this earth.

But there are particular indicators of whether
or not a plant has sufficient water available.

These indicators are a direct result of the role
that water or lack of water plays in plant
growth.



A dying plant indicates a water issue. ©iStock

       Here's a listing of common symptoms of water-related stress on plants:

  • decreased growth
  • small, off-coloured leaves
  • decline from top down
  • early fall colour
  • reduced xylem growth = long-term growth reduction
  • stress may show up five or more years later.

  • root activity slows or shuts down, and plants show symptoms of drought
  • decline in root growth slows plant growth processes
  • leaves may wilt from lack of water uptake
  • root rots are common in some species
  • lower interior yellow leaves