Xanthorrhoea - An iconic Australian native

The Xanthorrhoea or 'grass tree' is endemic to Australia. The plant was called a 'blackboy' for many years as the trunk of the grass tree resembles an aboriginal boy holding a vertical spear. The term 'blackboy' is now considered politically incorrect and 'grass tree' has become universally accepted. Aboriginal names for the plant include balga, yakka or yacca. There are a number of species and several subspecies.

Grass TreeCredit: http://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Kinglake_NP_Austral_Grass-trees.jpg/240px-Kinglake_NP_Austral_Grass-trees.jpg

The plant is very slow-growing, perhaps 1 to 2cm per annum, but it has a lifespan of some 600 years. An accumulation of leaf bases form a hollow ring. A natural resin exuded by the plant holds the leaf bases together which then becomes the trunk. The trunk has a very rough surface. Depending on the species, some trunks branch as a matter of course, some branch only if the growing point is damaged in some way and some don't branch at all.

Blackboy - cross sectionCredit: http://commons.wikimedia.org/wiki/File:Xanthorrhoea_trunk_cross-section.jpg

Long cyclindrical reed-like spikes form a 'skirt' round the bottom of the plant and a long stalk develops from the middle of the skirt. This flowering stalk may grow 2cm daily and may reach four metres high. Flowers appear at the top above a bare section which is known as a scape. Flowering can be stimulated by bushfire; otherwise grass trees flower at different times according to the species but typically every two to three years. After a fire, the grass tree is quick to respond, providing badly needed nutrients for birds, insects and bees. The flowers of the grass tree are tiny. The yellow to white florets become seed capsules containing hard, black seeds.

Blackboy flower spikeCredit: http://upload.wikimedia.org/wikipedia/commons/2/23/Xanthorrhoea_Flower_Mid.jpg

The root system is unique as the roots are surrounded by microbes called mycorrhiza. Mycorrhiza protect the plant from disease and pests. One reason so many grass trees eventually die when transplanted is because there are too few mycorrhiza in the surrounding soil to give it the protection it needs.

The grass tree is widely recognised as an Australian icon and appears on many items destined for the tourist trade. It is also becoming increasingly popular as a feature plant and now graces many a public park or streetscape. It has a coarse, rugged beauty that adds character to both commercial and domestic displays. Added benefits are its low water requirements once established and its low maintenance needs.

If considering a grass tree for your garden, bear in mind that they prefer full sun but will tolerate semi-shade. It is imperative to use well-drained soil. If the soil is sandy, add some garden mix. This will help with water retention and will also supply nutrients.

If planting in clay you will need to take special measures. Make a mound 0.6 to 1 metre high and the same wide. Then plant your grass tree at the top of the mound. Cut down the amount of water you give it and you should have no problems with drainage.


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Once purchased (or dug up) grass trees need to be planted with a minimum of delay. You may be satisfied that your plant is going to live, and so they might for five or six years, then they will show signs of stress and ultimately die. So prepare the hole ahead of time and deep water immediately after planting.

If moving a tree from its natural habitat, you need to excavate a substantial amount of soil from around the plant. Take all soil for at least one cubic metre round the plant. This should pick up the very deep underground roots. By saturating the area round the grass tree, it will be easier to take up as much of the root system as you can manage.

If the plant is dug up with too little of the surrounding material, the plant will eventually die. Mycorrhiza in the soil can be supported by mixing a cup of brown sugar with about ten litres of water. Pour this around the base of the plant.

Grass trees are often sold commercially in large containers or bags. Cut away the bottom (and the top if applicable) and plant the whole thing, ensuring the root ball is at ground level. This will help hold the earth around the roots and minimise disturbance to the root system.

Compact the soil round the root ball. This is to ensure there are no air pockets. Water well as this will help get rid of air pockets too. During the dry season, water thoroughly several times a week. Be sure to thoroughly wet the surrounding area. A plant of several metres height will need 30 to 50 litres of water a week until it is properly established.

Every three to four months, fertilise with a slow release fertiliser. Australian native plants generally need a fertiliser that will supply trace elements without adding too much phosphorous. Such fertilisers are now readily available.

Help your grass tree avoid picking up fungal diseases by keeping the centre free of debris and rubbish. Surrounding trees can drop leaves and spent blossoms on the grass tree and these should be removed. Apply pesticides to the foliage if necessary. Spraying with white oil will kill or discourage scale insects.

For the first year or two, cut off flower stalks and cones. Prune the leaves back. If there are large amounts of dry and brown leaves, trim by up to 50%. This will encourage new growth which, if conditions are optimal, may be up to 2 ½ cm per annum.

To germinate grass trees from seeds, collect seeds when the flower spikes turn brown Tap the spike and the seeds will fall. When ready to plance, scatter the seeds over seed-raising soil, cover lightly and water. These seeds may take up to 12 months to germinate. You may want to label your trays or pots so you are reminded of what treasures they hold.

The grass tree provides many things to bush creatures. Lizards and insects shelter in the mass of foliage. Birds, bees, butterflies and ants are attracted to the nectar provided by the flowers.

The grass tree was of great importance to aborigines in years gone by.

  • The light straight stalk was used for the butt of spears.
    The flower stalk, once it had dried out, was easy to ignite with a drilling stick to produce a fire.
  • The base of the trunk supplied resin. This was melted and used as a waterproofing agent for bark canoes and water vessels. It was also mixed with other elements to make a glue for stone spear- and axe-heads to wooden handles
    Food was obtained from the white, tender leaf bases and juicy roots.
  • Flour was made by grinding the seeds.
  • Edible grubs could be found in the centre of the plant and were indicated by dead leaves.
  • Carpenter bees made nests in the soft pith of the flower stalk. This provided globules of honey.

Early settlers added new uses of their own. The resin was burned during church services giving off a pleasant aroma and was also used as a base for producing varnishes and stove polish. It was used for sizing paper, and in the manufacture of soap and perfume.