Due to the ongoing drought gripping much
of Australia native grasses have become very popular as garden
plants due to their drought tolerance.
However, even though the average native
grass is vastly more drought tolerant than the average exotic
plant, there is still quite a wide range of drought tolerance
among them.
Poa labillardieri
Poa labillardieri has become a
very common native ornamental grass and there is the wide
spread perception that it this particular native grass can be
planted any where and it will thrive and look great.
Unfortunately this is far from the
truth. Poa labillardieri is at the lower end of the
native drought tolerance scale. In fact it is normally found
growing in areas that are quite moist on average.
Such areas include:
- Riparian zones, or in other words
flood zones on the lower banks of streams and billabongs
etc.
- At the bottom of hills and in
depressions where rainfall accumulates.
- In drainage channels where rainfall
drains from gentle slope.
Such areas are usually very hot and dry
over summer but, not withstanding drought, they become quite
wet over winter.
Where to plant Poa
labillardieri
Poa labillardieri will indeed
easily withstand hot dry summers and will almost certainly
withstand periodic droughts as long as it gets its feet wet
most winters. It is highly unlikely to survive long term in
permanently dry sites like steep exposed hills, e.g. freeway
embankments.
So when deciding whether or not to plant
Poa labillardieri and where to plant it in your garden,
you must consider the hydrology. Ask yourself where is rain
water likely to accumulate. Look for clues like lush plant or
weed growth in defined areas. Watch where water is pooling
when it rains. Dig down into your soil and look for
particularly moist patches. These are the areas where Poa
labillardieri is likely to thrive.
Native grasses that you might consider
for permanently dry areas include Themeda triandra /
Kangaroo Grass, Bothriochloa macra / Red Leg Grass, Dicantheum
sericium / Silky Blue Grass and Chloris truncata /
Windmill Grass.
Maintenance of Native Grasses
Native grasses, and ornamental
grasses in general, are not maintenance free. Over time spent
flowers stalks and foliage build up, increasing the content of
dry matter in the tussocks.
In fact if this dry matter is
not removed by grazing, pruning or fire it can cause the
tussocks to become senescent or dormant. This results in dry
dead looking tussocks that look very unattractive.
But that is not all. The build
of of dry matter, particularly in senescent tussocks, makes
the grasses highly flammable. Hence you garden can pose a
significant fire risk.
A mass planting of Poa on
the Princess Highway, as it enters the city of Geelong, has
been removed for this very reason. Motorists flicking
cigarette butts out of their vehicles were frequently setting
off grass fires in summer.
There is one very simple
solution and that is to prune your native grasses back
annually, in summer to eliminate the dry matter and encourage
the grasses to re-sprout as moisture level improve from late
April on. This can be done with a brush cutter, hedge clippers
or hedge trimmer. It is also a good idea to singe the stumps
if possible as this provides an additional stimulus to
re-sprout. Splash a bit of metho or turps over the stumps and
let them burn for a minute or so.
If you are unable or unwilling
to carry out this annual maintenance regime then the grass
like Lomandra are a better choice. These are slower
growing but do not produce as much dry matter nor burn any
where near as ferociously.
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Planting New Plants
- Dig the hole, bung the plant in,
backfill and then water.
The problem with this technique is
that the garden soil mixes, used to create garden beds,
often become extremely water repellent once they dry out. If
you look closely you will notice that the water tends to
pool on the soil surface or run off with very little
actually penetrating significantly down to the root zone of
your new plant.
So potentially your new plant has
received little or no water despite the hose gushing water
over it for several minutes. As a result the plant will
suffer transplant shock and die within a few days.
How do you fix this problem? Dig the
hole and fill it with water as many times as necessary for
the water to penetrate the surrounding soil and thoroughly
soak it. Also soak the pot in a bucket of water prior to
planting. See "Water
Repellent Soil" for tips on how to make your soil
easier to wet.
- Leaving the surface of the potting
mix exposed to the air.
The potting mixes used to propagate
plants are highly porous and very prone to drying out. So
planting such that the surface of the potting mix is exposed
to the air will result in the root ball of the young plant
rapidly drying and killing the plant. Tube stock is
particularly vulnerable due to the small volume of potting
mix.
Make sure you wet the surrounding soil
thoroughly and cover the surface of the potting with a layer
of garden soil and preferably some mulch as well.
- Over fertilising Australian native
plants.
Most Australian native plants are very
well adapted to soils with poor fertility. Frequently
fertilising them with lots of fertiliser can in many cases
be harmful to them.
In particular many Western Australian
plants are so efficient at gleaning what little phosphorous
there is in the soil that they will actually suffer
phosphorous poisoning if you use fertilisers with a high
phosphorous content on them.
Organic fertilisers, such as blood
& bone, are ideal for many Australian native plants as
they act as slow release fertilisers.
Many Australian native plants will
respond nicely to a good hand full of blood & bone at
the time of planting. But make sure you place it at the
bottom of the hole rather than sprinkling it on the soil
surface after planting.
Once established you should fertilize
them perhaps once a year. If you use green waste mulch on
your garden beds then you probably needn't bother
fertilizing your garden beds at all. The rotting green
material will provide all the nutrients that the plants
require.
There are very few 'heavy feeders'
among our Australian native plants and regularly and/or
heavily fertilising your garden beds is more likely to harm
native plants as well as encouraging prolific weed growth.
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Incorrect Assumptions
- Assume that Australian native
plants are highly drought tolerant even in nursery pots.
The drought tolerant nature of many
Australian native plants is due in a large part to their
deep root systems that can reach moisture deep down in the
soil profile.
So clearly a newly planted plant, with
a root system only a few centimetres deep, is not going to
be particularly drought tolerant and will require periodic
watering to get it established.
This also applies to Australian native
plants in containers. Their root systems are severely
restricted and they will require more frequent watering than
if they were planted in the ground.
- Australian native plants require
no maintenance.
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Cause
This is a major problem with garden soil
mixes available from landscape material suppliers. The problem
arises from the fact that their soil mixes often contain lots
of sand, lots of organic matter but very little clay.
The sand particles become coated in a
layer of fine organic material rendering them hydrophobic or
'water hating'. There is really only one way to solve problem
this permanently and that is to increase the clay content of
your soil. Clay particles are hydrophilic or 'water loving',
and being so minute, they will eventually penetrate the
hydrophobic coating on the sand particles and break it
down.
You increase the clay content of your
soil by obtaining some black or yellow clay, soaking it in
water and then pouring the resulting slurry over your garden
soil. You may have to do this many times to build up the clay
content of the soil.
Granitic sand is a good alternative for
the regular soil mixes. Despite being a sand it has a high
clay content and is very easy to wet, even when bone dry. You
can mix it with lots of compost or your existing garden soil
to prevent it forming a hard surface crust. It costs any where
between $40 and $70 per cubic metre from most landscape
material suppliers.
The other benefits of granitic sand
include being low in nutrients, ideal for native plants, as
well as being weed free. The regular soil mixes from the
landscape suppliers nearly always contain copious amounts of
weed seeds, often including declared noxious weeds.
Another way to add clay to your soil is
with a product called Volclay bentonite:
This is purified clay
that comes in granulated form and is normally used by farmer
to seal leaks in their dams and by the wine industry as a
fining agent.
It be can easily mixed through
dry garden soil with a rotary hoe at a similar rate as you
would use gypsum in clay soils. If you combine it with plenty
of organic matter then the worms will do the rest of the job
and mix the lot into a rich water absorbing top soil.
If you have an established garden and
can not easily mix the stuff through the soil then here is an
alternative method. It you take a cup of bentonite, mix it
with several cups of water and leave it to soak overnight you
will end up with a paste with the consistency of smooth peanut
butter. If you then add several cups more water, mix it with
the bentonite paste and leave it to soak overnight again you
will end up with a paste with the consistency of yoghurt.
If you keep going then sooner or later
you will produce a thin slurry that you could pour from a
watering can. Simply water your garden with this slurry and it
will incorporate into your soil nicely.
Or you can simply use the bentonite
granules in place of water crystals. One 25kg bag, at around
$30, will go a much further than a small and expensive packet
of water crystals. Bentonite is also a natural product while
the water crystals are made from synthetic polymers.
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There are 3 things that must be taken
into account when considering using grey water on your garden.
They are the sodium, phosphate and pH levels.
Sodium
Salt is, in reality, a general term used
in chemistry to describe ionic compounds. Copper sulfate or
bluestone as well as sodium carbonate or washing soda are both
salts. However, in the minds of the general public, the term
salt has become inextricably bound to sodium chloride that we
sprinkle on our food every night.
High levels of sodium are toxic to
nearly all plants except for those that live in marine
environments like sea weed and mangroves.
Most washing detergents contain sodium
in two forms. As sodium carbonate or washing soda along
with sodium laureth sulfate that is the actual detergent
in the mixture. The sodium carbonate produces a high pH at
which the sodium laureth sulfate works most efficiently.
The amount of sodium in sodium laureth
sulfate is quite small and nothing to worry about. However
many washing detergents, in particular the powders, contain
very large amounts of sodium carbonate and you normally use a
large amount of the powder in each washing cycle.
Phosphate
Dish washing detergents can also contain
high levels of phosphorous in the form of phosphates. These
salts act as a chemical buffer system that maintains the high
pH during the washing cycle.
For most plants this will probably be
beneficial. However for some Australian native plants, most
notably Banksias from Western Australia, the large amounts of
phosphorous could become quite toxic to them.
Such plants grow in soils with very low
phosphorous levels and have evolved extremely efficient ways
of gleaning what little phosphorous is available. So in soils
with abundant phosphorous they absorb so much that toxic
levels accumulate in the plant.
pH
pH consists of a scale of 0 to14 and
gives a measure of the acidity or alkalinity of a substance.
Strongly acidic liquids like hydrochloric acid or 'spirits of
salts' will have a pH of 0. Strongly alkaline salts like
sodium hydroxide or 'caustic soda' will have a pH of 14. Tap
water is generally neutral and will have a pH of 7.
Decaying organic matter produces humic
acid will therefore absorb and neutralize most of the
alkalinity in laundry water. Hence gardens that have plenty of
compost or mulch are ideal for irrigation with grey water.
None the less the high pH of laundry
grey water can be an issue for sensitive acid loving plants
like Rhododendrons. However for most plants the temporary rise
in pH will not be an issue.
Choosing a washing detergent
Please refer to the Lanfax Laboratories web
site in order to choose the most appropriate laundry
detergent. This company has done an analysis of the sodium,
phosphate and pH levels of average washing cycle, both top
loading and front loading, using a large range of wash
detergent products.
It is a simple matter of examining the
graphs and choosing a product that has the lowest sodium
levels per washing cycle.
Grey Water Irrigation Systems
The simplest means of irrigation with
grey water is to gravity feed it out through the inspection
port of your pipes that drain your bath and shower,
laundry trough or kitchen sink.
This obviously requires that the pipes
are accessible and that there is sufficient vertical
separation between the inspection port and the garden bed. And
you will need to move the end of the hose around to different
locations on a regular basis.
Use 25mm hose rather than the standard
13mm hose and you will find that the drainage rate is the same
or at least very close to normal.
Rubber funnel
PVC drain diverter with a rubber funnel
The most abundant sources of grey water
in the average household are the laundry and the bathroom, and
for these sources it is well worth while incorporating a pump
to distribute the water more broadly.
This can be done via a polypipe
irrigation system to which you can attach a standard garden
hose, through an ordinary garden sprinkler or a soaker hose.
With a pump, vertical separation between
the PVC outlet pipe and the garden bed, is no longer an issue.
The inlet of the above pump is attached to a household outlet
pipe that is at ground level.
Laundry water contains a great deal of
lint that will clog your irrigation system so filtering is a
must.
A sieve in the plug hole of your laundry
trough will catch the coarse lint and is very easy to clean
after each wash. It may be necessary to weigh this down to
prevent it being dislodged by the flow of water.
An inline filter before the pump inlet
will catch any remaining finer lint and will require cleaning
every few washing cycles. If you forget about the sieve then
the inline filter will become completely clogged very quickly
and thoroughly and you may well have to clean it more than
once per washing cycle and with difficulty.
A simple system like this will cost you
between $120 and $200, using the above inexpensive pump.
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With the benefit of a
university education and highly varied work experience I am
able to better analyse every day things and every day
situations.
As such, it is always amusing
to me how people assume that common household products are not
chemicals, in the same way as the herbicides I use regularly,
and therefore completely without environmental side effects or
health risks. E.G. Vinegar as a herbicide.
Allow me to familiarise you with the key component of vinegar
and you will never look at it in quite the same way again.
It is acetic acid, also know as ethanoic acid, and derived
from the artificial or natural oxidation of ethanol or common
alcohol. Acetic acid is also one of the two raw materials in
the manufacture of asparin or acetylsalacylic acid.
In its pure form acetic acid is a highly corrosive, highly
flammable and highly volatile liquid. It is comes into contact
with the skin it will cause severe burns while the fumes can
cause severe to fatal burns to the mucous membranes of the
nose throat and air passages. If swallowed in sufficient
quantities it is fatal. The liquid and fumes can be explosive
under certain conditions.
Potential Health Effects
Inhalation:
Inhalation of concentrated vapors may cause serious damage to
the lining of the nose, throat, and
lungs. Breathing difficulties may occur. Neither odor nor
degree of irritation are adequate to indicate
vapor concentration.
Ingestion:
Swallowing can cause severe injury leading to death. Symptoms
include sore throat, vomiting, and
diarrhea. Ingestion of as little as 1.0 ml has resulted in
perforation of the esophagus.
Skin Contact:
Contact with concentrated solution may cause serious damage to
the skin. Effects may include
redness, pain, skin burns. High vapor concentrations may cause
skin sensitization.
Eye Contact:
Eye contact with concentrated solutions may cause severe eye
damage followed by loss of sight.
Exposure to vapor may cause intense watering and irritation to
eyes.
Chronic Exposure:
Repeated or prolonged exposures may cause darkening of the
skin, erosion of exposed front teeth,
and chronic inflammation of the nose, throat, and bronchial
tubes.
Aggravation of Pre-existing Conditions:
Persons with pre-existing skin disorders or eye problems, or
impaired respiratory function may be
more susceptible to the effects of the substance.
Environmental Effects
If you spray sufficient quantities of vinegar
in your garden, over a sufficiently long period of time, then
you will lower the pH of the soil and potentially kill many
plants.
If you neutralise the vinegar with garden lime then you will
end up with calcium and magnesium acetate. Acetate salts of
the alkali earth metals are highly soluble and easily moved
around by water.
Acetate is clearly not a plant nutrient and I am unsure about
what long term effects large quantities of acetate will have
on the health of plants, of the soil and of local water ways.
But it would be very interesting to find out.
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