Grass trees / Xanthorrhoea
Where to plant Poa labillardieri
Maintenance of native grasses
Appropriate native plants
Planting new plants
Water repellant soils
Weed seed bank
Cut & paint
Using grey water
Choosing a washing detergent
Applying grey water to your garden
Grass trees grow in very arid areas with dry stony or gravelly soil and they are absolutely intolerant of wet feet.
On top of this they, along with a number of other native plants, are extremely sensitive to the introduced soil fungus called Phytophthora cinnamomi which can thrive in the damp to wet soils of suburban gardens.
Phytophthora cinnamomi has been introduced to Australia since European settlement and it is the small pox of the plant kingdom. A number of Australian native plant species, along with citrus fruit trees and avocado trees, have little or no resistance to this fungus which absolutely decimates their populations once introduced to an area.
It is readily spread by Earth moving equipment, four wheel drives, trail bikes, mountain bikes, hikers, running water and by ignorant individuals within the nursery industry transplanting grass trees! So if you are intending to purchase a grass tree, I suggest you be very careful who you get them from. Ask the seller if they have been officially verified as Phytophthora free.
A Phytophthora infection gradually creeps through the soil and you will notice any susceptible plant species progressively succumbing to the fungus as the infection radiates out through the soil from the source:
Elimination Phytophthora cinnamomi is difficult and by no means guaranteed. But if you notice your grass trees etc. suddenly starting to yellow then you need to act quickly. The recommended method is to treat the soil around and beyond the affected plants with Fongarid.
If you are in and area with clay, loamy or silty soils, then the best way to plant grass trees is in large pots with some sort of gravel that you might otherwise use to create a path or a driveway - low in nutrients and free draining. Alternative you can create some sort of raised garden bed filled with gravel and plant the grass trees in that such that their roots are completely above the existing soil.
However if your existing soil happens to be already infected with Phytophthora cinnamomi then it is unlikely that this will protect the grass trees from it in the long term. In this case you would be better off planting a native species that is resistant to Phytophthora.
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.
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.
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 dry matter, particularly in senescent tussocks, makes the grasses highly flammable. Hence you garden can pose a 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.
- If you have a new garden bed that was previously infested with large weeds then don't immediately plant small ground covers and bedding plants unless you are prepared to put in a large amount of weed control effort to keep the weeds at bay for the first few years.
- If you turn your back on the garden beds for any length of time then you will find that your native plants are swamped by weeds and struggling to survive.
- If you are unlikely to be able to put in the required weed control effort then plant larger denser shrubs that will have a better chance of competing with the weeds.
- 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.
- 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.
- 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 centimeters 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.
It may be the case that many native plants don't require constant watering and fertilizing as do many exotic species, but the one thing that most native plants do require is regular, though not necessarily frequent, pruning.
Many native plants have a tendency to get quite straggly if they are left to their own devices for many years. But most do respond well to pruning and many to quite harsh pruning. Hence they need to be regularly pruned to maintain a compact and aesthetically pleasing growth habit or to remove any dry foliage and spent flower stalks.
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.
Yet 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.
If weeds have been growing in area for a significant period of time then the soil will be full of dormant seeds from those seeds. Not all the seeds are 'timed' to germinate after different periods of dormancy. This is called a 'seed bank'.
The result is that you can't just spray all the existing weeds once and then assume the job is done. In actual fact it can take decades for the last of the weed seeds have germinated and the seed bank becomes exhausted. And this assume that, in those decades, the weeds have not been allowed to make further deposits of seeds into the seed bank.
It is therefore important that you do follow up weeding for as long as it takes to exhaust the weed seed bank. And make sure you do the weeding when the weeds have begun flowering or before. Don't wait until they have dropped another few hundred thousands seeds into your soil.
Unfortunately herbicides are a necessary evil unless you have many hours available and the will power to hand weed. But, in Australia, all herbicides are biodegradable and will not do any long term harm to your soil or yourself unless you are spraying them constantly on an agricultural scale.
Herbicides should be views as a means to an end and always combined with other weed suppressing techniques to minimize their use as far as possible. One other weed suppressing technique is maintaining a thick layer of mulch over your garden beds. As long as the mulch is several centimeters thick when your first lay it then plastic weed mat is completely unnecessary.
Let's look at glyphosate as an example.
The full name of glyphosate, in chemical nonclemature, is N-(phosphonomethyl)glycine. Note the 'glycine' bit - sounds as scary as the rest of the name doesn't it. Glycine is in fact one of the amino acids that forms proteins in the tissues of all animals and plants. So glyphosate is nothing more that chemically modified glycine.
When a plant tries to make its proteins with glyphosate molecules, rather than proper glycine molecules, it is like constructing a building with defective construction materials. The protein falls apart and the plant eventually dies as a result.
Now glyphosate is certainly not a health tonic for humans but nor is it particularly poisonous to us. Sensible precautions that you would use for handling your laundry chemicals is adequate to safely handle glyphosate.
Glyphosate will also have short term effects in the soil however it rapidly biodegrades and those effects quickly diminish and disappear.
Hand weeding is a useful technique for those weeds that you can pull out easily - mainly annual weeds.
However don't waste your time trying to hand weed rhizomatous weeds like couch and kikuyu because you will never be able to remove all the rhizomes and they will rapidly re-grow from those remaining behind in the soil. Glyphosate is really the only practical solution to these two weeds in particular. The glyphosate is translocated (or moved) through all the rhizomes and kills all or most of them.
Nor should you waste your time trying to hand weed those weeds that have deep bulbs like soursob and onion grass. Again metasulfuron methyl is the best herbicide for these weeds. This herbicide is slow acting and allows enough time for it to be translocated into the bulbs before it starts causing symptoms. If you use glyphosate on these type of weed all you will do is burn the foliage off and new foliage will soon sprout from the bulbs.
This is a useful technique to use on woody weeds. You cut them down as close to the ground as possible, with a chainsaw or loppers, and then, within seconds, paint the stumps with neat glyphosate (not the ready to use stuff). Nine time out of ten the weedy tree or shrub will not recover and, if it does, you simply repeat the process on any re-growth. You only need to paint the bark ring and not the entire cross section of the trunk.
This has the additional advantage of tightly targeting your use of glyphosate such there will be little or no effect on the soil.
This is a useful technique for annual weeds, that only live for one year, and where all you need to do is prevent them from setting seed. It is handy where it is difficult to use herbicides without damaging other plants that you want to keep alive.
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.
Salt is, in reality, a general term used in chemistry to describe ionic compounds. Copper sulphate 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.
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 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.
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.
Be aware that grey water is full of lint that will clog filters, sprayers and drippers very quickly so it is best to simply run the grey water through an open hose directly on to the garden. Even the expensive grey water collection systems you will still have major problems with blockages due to lint so don't bother.
Also be aware that, if you use a simple hose, you need to move it around different parts of the garden so that sodium and phosphate etc. does not build up to high levels over time. And also mix grey water irrigation with tank water or mains irrigation.