[Music playing]
(Kevin Handreck) No wonder these plants in
the Adelaide Conservatory look so lush,
there’s an automatic watering system that
provides them with as much water as they need.
But more importantly there’s a fogging system
that maintains very high humidity around their leaves all the time.
And that means that they’d lose very little water.
The plants in our gardens are nowhere near as fortunate as that.
Australia’s sunny skies and often very low humidity
means that our plants lose large amounts of water,
and what rain doesn’t replace we must provide through our sprinklers.
The question is how much water do we need to provide,
or put the other way around,
in a country where water is very expensive
and there’s not that much of it,
how little do we need to provide to just
maintain our plants in the condition that we would like them to be in.
Think of the soil under your garden as a large reservoir of water.
Some of the reservoir space is taken up with solid particles of soil,
but between them are holes called pores
that are filled either with air or water.
When rain falls, or when we water our garden,
the water moves down through these pores.
A rain shower giving five millimetres of water will on average
wet the soil to a depth of amount 20 millimetres.
[Music playing]
Most of the roots of typical garden plants
are within the top 500 millimetres of the soil,
so that’s where we need to put our water.
Now it would take about 125 millimetres of water
to percolate down to about that depth.
To get the most out of the water that you’re putting onto your garden
you must know the rate at which your sprinklers are delivering that water.
Now for a lawn like this,
the simplest way of getting that rate is to use a can test.
You can see here we’ve got a grid pattern of cans
all over this lawn here;
they can be any shape and size of can, as long as they’ve got straight sides.
What we’re going to do is to turn the sprinklers on here for an hour
and measure the depth of water that is put into each of these cans.
[Sprinklers watering the lawn]
Well the sprinklers have been on for an hour now.
What we need to do now is
to measure the depth of water in each of the cans.
Now I’ve done this before and I know that these sprinklers
deliver about 20 millimetres of water each hour.
Now if I want to moisten this soil to a depth of 500 millimetres
I need about 125 millimetres of water,
so these sprinklers need to go on for about six hours
to fill up that soil to that depth.
That amount of water will keep this lawn going for three to four weeks
in a typical Adelaide summer.
In most parts of Australia water is becoming more expensive,
and we’re paying for every drop we use.
That’s a very good incentive for keeping use to a minimum.
The most powerful way of reducing water consumption in your garden
is to delay watering until the plants are wilted, like this one here.
What happens then is that the plant can’t get water from the soil,
or it can’t get very much, and so it sort of shuts up shop for a while.
Of course it grows more slowly,
but at least it uses a lot less water than it
would otherwise if you kept the soil very moist.
Now this sort of strategy is not for you if you want a lush garden.
[Walking through the bush]
The second most powerful
way of reducing water consumption in the garden
is to have a thick mulch on the surface of the soil.
A mulch such as this here can reduce evaporation of water
from the soil by about 70%.
If we dig down here we can see that the soil is still reasonably moist,
even though this is the middle of the summer.
So the important points to remember are these –
know how much water you’re putting onto the soil,
fill up that reservoir to its total content,
and then let the plants dry it down to as far as you dare go.
And of course in the garden beds, have a good mulch right over them.