water
Water is an essential source of life and, likewise, soil water is of vital importance for plant growth and survival. Soil can be described as a ‘leaky’ storage place for water. It leaks through evaporation, transpiration (water absorption by plant roots), run-off, and drainage. Hence the quantity of water left behind in the soil is available for use by plants, and is termed PAW, which stands for Plant Available Water.
Plants need water to support them in an upright position. In the absence of PAW, the plant starts to wilt. At this point, if additional water is not supplied to the soil speedily, plant tissues will loose their ability to recover and these plants will die.
Soils hold water in two different ways:
| 1. | within the soil organic matter, i.e. in dead and decaying plant and animal remains as well as the humus (partially decomposed organic soil material) in the soil; |
| 2. | held in a thin film upon the surface of each of its mineral particles, i.e. sand, silt, and clay. |
How do you improve soil
water holding capacity?
Whether your garden soil has a greater proportion of sand or clay, there is a ready way to improve its water storage ability. The solution is adding more organic matter.
Organic matter
Can be added in the form of mulch (a thick layer of organic matter applied to the soil surface) and:
- acts as an insulating layer
- reduces surface evaporation of water from the soil surface
- recycles nutrients back into the soil
Too much water is bad for your plants
Plant roots need air to breathe. As water drains through soil it takes fresh air down with it, renewing the air in the cavities and spaces between the soil particles and providing plenty of air for plant roots. However, if there is too much water for a prolonged period of time the plant roots will suffocate and the plant will die, unless the plant is of a type adapted to waterlogged conditions, e.g. water lilies.
How much water do I need to apply?
In general you only need to apply water during the months of spring (September-November) and summer (December-February), when the quantity of water evaporated from plants and soil (potential evapotranspiration (PET)) usually exceeds the quantity replaced by rain. The current levels of PET and rainfall are usually published in your local daily newspaper. See below for the method used to detect the levels of water you need to apply:
| Total rainfall over a given time (e.g. week) | – | Total PET over a given time (e.g. week) |
= | Amount of water needed to be applied at the end of a given time (e.g. week) |
Note: As a rough guide, the maximum amount of water your garden needs per week is around 15 mm (rainfall plus irrigation) in October, and this will increase (dependent on weather conditions) up to about 35 mm (including rainfall plus irrigation) per week in December and January.
Can gardening cause water contamination?
YES! Over-watering that occurs when you let the water run too long or when water is applied faster than the ground can absorb leads to run-off and leaching (downward movement through the soil of a dissolved substance). Water run-off tends to contain soil, pesticides, and fertilisers that can contaminate our waterways and oceans. Leaching can contaminate ground water with fertilisers and pesticides.
- Contaminants make water unsuitable for drinking (e.g. excess nitrate levels in drinking water caused blue-baby syndrome), recreation, agriculture and industry.
- Residues from fertilisers can over stimulate aquatic plant growth, making the water unsuitable (e.g. depletes oxygen level in the water, reduces sunlight penetration) for fish and other aquatic life
- Contaminated water can reduce or wipe out aquatic life by killing or reducing its reproductive ability.
- Consumption of fish and other aquatic life from contaminated water can result in human heath risks
- Water plants only when they really need it.
- Hand water your plants whenever possible.
- Check your soil and weather forecasts before watering your plants.
- Avoid run-off by applying water slowly.
- Water plants on calm days, either during the morning or the evening, and reduce water loss evaporation.
- Reduce lawn areas and plant trees, shrubs, and groundcovers instead because lawns require more water.
- Choose low water-use plants – ask your friendly garden shop assistant.
- Apply mulches, grass clippings and straw to conserve ground moisture and discourage weeds from germinating.
- Avoid using sprinklers if possible, because they result in water run-off.
Instead use soaker hoses or drip irrigation.
Collect rainwater from your roof and use it to water your plants. - Avoid watering frequently in small amounts because they tend to make plants more susceptible to drought by encouraging shallow rooting.
- Use low flow sprinklers.
- Use a timer on irrigation systems.
- Use an irrigation timer fitted with a ‘rain switch’ so that the sprinkler will automatically switch off when it detects rain.
Save our precious water by minimising water run-off from your land. In
return, your garden will flourish with improved soil/plant health and
reduced weed growth.