Ensuring that your plants are getting the right amount of water

 
All plants need water to grow, and to survive. The amount of water needed however, will vary from plant to plant. The two main things which affect how much water a plant needs are:
 
1. The variety of the plant.
Some types of plants have the ability to retain water within their tissues for later use. Other plants are unable to do this.

2. The environment in which the plant is growing.
If there is plenty of water available around the plant, e.g. high humidity and rainfall and low temperatures, then it will remain moister than a plant growing in exposed, windy, sunny situations.

A plant can suffer from a lack of water. A plant can also suffer from an excessive amount of water. When you water a plant it is important to strike that delicate balance between too little and too much. Over watering can be just as bad as under watering.

Symptoms of Water Deficiency
The first symptom is usually that the rate of growth slows. This is usually a mild case only a slight deficiency.
Stems become slender, leaves become smaller, flowers and fruit become smaller.
If a plant, which has a watery type of fruit (such as a tomato), is under watered, the plant can begin to take moisture out of the fruit (ie. the tomatoes begin to shrivel).
 
Wilting
In extreme water deficiency, the tips of the plant can die back; and perhaps the whole plant might die.

Symptoms of Water Excess
  • Seedlings can become leggy if they are planted close together in the nursery, and if there is too much moisture about.
  • Plant tissue cells can become enlarged and in extreme cases they might burst.
  • Internodes become elongated (ie. the spaces between two leaves on a stem become elongated or stretched out).
  • In extreme situations leaves can blacken, plant can die back or die off completely.

Maintaining Appropriate Water Levels
  • Consider the soil where a plant is growing. If a plant is getting too wet, perhaps the soil should be more freely draining. If the plant is getting too dry, perhaps the soil should have a better capacity to retain moisture.
  • Consider the frequency of watering. Maybe you need to water more often or less often.
  • Consider water penetration. Does the water you apply get absorbed into the soil or does it run off and get lost? Does it land on the leaves of plants and get deflected away from the soil? Does the sun or wind remove it before the plant gets to use it?
  • Is the plant in a shaded situation? Is it in a very hot situation? How much natural rainfall has it been getting?


ESTIMATING PLANT WATER REQUIREMENTS
 
The amount of water required by a plant is affected by many things including the following:
1. The Type of Plant
  • Some plant varieties utilize more water than others.
  • Some plants have a greater resistance to dry conditions (e.g. cacti and succulents are extreme examples).

2. The Rate of Growth
  • If a plant grows rapidly (perhaps because of its variety, or perhaps due to optimum growing conditions in terms of fertility, climate, etc), it will use water at a faster rate.

3. Climate
  • In high temperatures soil loses water through evaporation.
  • In windy conditions both soil and leaves of the plant lose water faster.
  • Higher levels of natural rainfall reduce the need to irrigate. (Make sure you know not only what the annual rainfall is, but also what the distribution of rainfall is throughout the year).

4. The Soil Conditions
  • Does the soil drain freely?
  • What is the soil's ability to retain water?
  • Is there a hard pan or high water table below the soil surface?
  • Does the soil repel water when dry (increasing surface run off)?

Learn more on water requirements for plants in Horticulture I.


Read more on Selecting the right plant for a particular position in the garden- What to Plant Where