How to grow grass trees

Growing grass trees in Perth

The grass tree Xanthorrhoea is a uniquely Australian plant, which epitomises the Australian landscape and is as tough as old boots. The Australian grass tree (formally commonly referred to as Blackboys) are indigenous to Australia.

If you have ever wondered how to grow grass trees in Perth then look no further. Grass trees are a relatively easy plant to grow, and there are a few tricks to successfully growing grass trees in Perth, Western Australia. Get these right and you will be laughing.

When to plant grass trees in Perth:

The best time for planting or transplanting grass trees is from autumn to early spring, as there is no risk of frost. With the right care you should be able to do it at almost any time of year in our Mediterranean conditions.

How much water do grass trees need:

If you are wondering if you can over water grass trees. The answer is yes. Once or twice a week is usually enough during summer, but make sure that you keep the actual trunk of your grass tree as dry as possible. Water on the trunk can soften it, leaving it vulnerable to pests and diseases.

Types of grass trees:

Xanthorrhoea is a genus of about 30 species of flowering plants endemic to Australia. Species are known by the name grass tree. Choosing which grass tree variety to plant is all about personal taste. Some descriptions of the more common grass tree varieties are provided below.

  • Acanthostachya grass tree – Xanthorrhoea Acanthostachya is native to South Australia and known as the spiky Grass tree. It has a short trunk with one or two crowns. The leaves are a grey green and shorter than other species, with a prickly flower spike that blooms between August and November.
  • Australis grass tree – Xanthorrhoea Australis is also from South Australia and known as the Australian Grass Tree or Kangaroo Tail due to its long, thin, grass-like leaves that grow up to a metre. It can take about 30 years for the leaf tuft to grow above the trunk. This is one of the slowest growing species with a growth rate of no more than two centimetres per year.
  • Glauca grass tree – Xanthorrhoea Glauca, known as the Grass tree, is widespread in eastern Australia. Its trunk can grow over 5 metres in height and its common to find this species with multiple branches. It makes a unique garden specimen with tall, rod-like flower spikes that rise above the foliage to produce masses of tiny, white flowers.
  • Gracilis grass tree – Xanthorrhoea Gracilis, nicknamed the Slender Blackboy, comes from West Australia. These Grass trees do not form a trunk but has tufted perennial grass growing from branches that form on the stem underground. The leaves grow up to 2 metres with a flower spike that produces creamy white flowers between October and January.
  • Johnsonii grass tree – This Western Australian species is a spectacular caudiciform plant with its leaf bases creating a trunk, similar in appearance to that of the cycad. Typically, they are single trunked specimens growing up to 4 metres, although multi-trunk specimens have rarely occurred. The Xanthorrhoea Johnsonii is toxic to cattle that graze on its leaves and its thought that the chemical produced by the plant is a natural deterrent so the juvenile plants can reach maturity.
  • Macronema grass tree – Xanthorrhoea Macronema is tufted and trunkless with flexible linear leaves that are 1 meter long and rise from the ground. Its long cream flower spike blooms from spring through to summer. This Grass tree is native to Queensland and New South Wales.
  • Preisii grass tree – Another species found in Western Australian is the Xanthorrhoea Preisii, known as the Western Blackboy. It has an unusual and striking trunk that becomes naturally blackened due to frequent bushfires and flowers in late Winter or early Spring.
  • Thorntonii grass tree – Xanthorrhoea Thorntonii is commonly known the Cundeelee Blackboy. These Grass trees are the only species to be found in central Australia, including the Great Sandy Desert, Great Victoria Desert and MacDonnell Ranges. It has a trunk reaching up to 5 metres, topped with perennial grass and a flower spike, which is over one metre and blooms between August and December.

How to grow grass trees at home:

If you are wondering how to plant a grass tree in the garden then look no further. Growing grass trees in the backyard has become increasingly popular over recent years.

  1. Choose a place in the garden that gets full sun to part shade to plant your grass tree. Prepare the planting area well by digging in a quality soil improver and plant fertiliser.
  2. Dig the grass tree planting hole twice as wide and to the same depth as the root-ball.
  3. Carefully remove the plant from the pot ensuring not to disturb any of the roots.
  4. Position the grass tree in hole and back fill, gently firming down down the top soil. Form a raised ring around the plant, creating a well so that water will go where it’s needed most at the base of the grass tree.
  5. Mulch lightly around the base of the plant with wood chips and water in well.
  6. Feed in Spring and Autumn with a quality Soil Improver and plant fertiliser to ensure strong healthy root development.

How to grow grass trees in pots:

Growing grass trees in pots is a great idea if you want to grow a relatively small grass tree. I love to grow grass trees in pots because it gives you the flexibility to move them around the yard for maximum impact.

  1. A grass tree in pot will need a pot that is at least twice the size of the selected plant. The best position to place is the pot is in a location that receives full sun to part shade.
  2. Fill the pot with a quality potting mix.
  3. Carefully remove the grass tree plant from the pot ensuring not to disturb any of the roots.
  4. Position your grass tree in hole and back-fill, gently firming down the top soil.
  5. Mulch the top of the pot plant lightly with wood chips and water in well.
  6. Feed in Spring and Autumn with a quality Soil Improver and plant fertiliser to ensure strong healthy root development.

How to propagate grass trees:

If you are wondering how to grow grass trees from seed then this is what you need to know.

  1. Seeds develop in capsules on the flowering spike in the months after flowering.
  2. As they grow, the capsules start to stick out from the surface of the spike and are easily visible. The grass tree seed is ready for picking when the capsule begins to open.
  3. Depending on the variety, there are usually 2 to 3 seeds per capsule.
  4. Grass tree seeds fit tightly in the capsule on the spike. You can prise the seeds out with tweezers or if the spike has fallen from the plant you just tap the whole spike on a plastic sheet until the seeds fall out. The seeds are around 5 mm and easy to handle.

Seeds can be sown all year round, but spring or autumn is best, as these months have less extreme temperatures for germination. The seeds germinate well without special treatment, but not all seeds will be viable. Therefore, it’s recommended to sow many seeds to a punnet and then pot up those that germinate.

Sowing Xanthorrhoea grass tree seeds:

  1. Fill a seed tray with a quality potting mix mixed with some sand to improve drainage.
  2. Gently compress the potting mix and moisten.
  3. Place the seeds flat (with widest part) on the surface.
  4. Cover the Xanthorrhoea seeds with a thin layer of soil (2–3 mm).
  5. Water the seed tray again with a spray bottle to ensure the seeds remain in place.
  6. A transparent plastic take-away container is a good place to put your seed container. Closing the lid will ensure moisture levels stay constant and help with germination.
  7. When the grass tree seedlings are 5-10 cm you can transfer them to individual pots

How to transplant a grass tree:

The best method of transplanting grass trees is as follows:

  1. Start by securing the leaves of the grass tree with string, to avoid damage to your eyes.
  2. Dig carefully around the base of the plant severing the old roots. You only need to dig around 5 cm away from the base of the trunk to avoid damaging it. Do not push on the top of the plant or attempt to rock it back and forth as you may snap it off.
  3. Wrap the root system of the grass tree in a damp hessian or canvas to stop it from drying out while transporting the plant.
  4. Plant the grass tree as soon as possible at the same depth at which it was growing. Fill in the soil around the root system with a high quality potting mix, keeping a hose running to moisten the soil and eliminate any pockets air.
  5. Make a depression or ‘saucer’ around the plant for future hand watering, to ensure the water goes to the base of the plant and doesn’t run off.
  6. Trim off the leaves, to reduce water loss. Within a few weeks new leaves will appear again from the centre of the plant.
  7. Water the plants regularly until the onset of heavy winter rains and then water once a week, starting in early spring and continuing through summer and autumn until the onset of further winter rain. After the first year once your plant is established it should be drought tolerant.

How to fertilise grass trees:

Grass trees are very hardy plants but if you want them to really thrive, you need to encourage root system development. Regular deep watering can help with this, I also recommend using a liquid seaweed fertiliser for the first few months after planting. Some people recommend applying a mixture of 1 cup brown sugar to 4 litres water to the soil surrounding your grass tree after planting – this feeds the mycorrhiza in the soil, boosting root growth.

When do grass trees bloom:

A common question a lot of first time planters will ask is when does a grass tree flower? This refers to the flower spike that can be up to two metres high which gross from the centre of the grass tree. It is a difficult question to answer as flower spikes often grow after the grass tree experiences stress, such as a bush fire.

As it’s often not practical to light a fire in your backyard, another way to stimulate flower growth is to place a 5-8 cm stone on the top of the growing tip. The stone can often cause enough stress that the flower will form.

As the plant becomes established, removing the flower stalks after the season helps reduce stress on the plant, enabling it to focus on establishing a healthy root system. If you remove the stalk remember to harvest the seeds to propagate grass trees for your friends and neighbours.

When to prune grass trees:

If you are wondering how to trim a grass tree unfortunately the answer is a bit complicated. There are three schools of thought on pruning grass tress. The first is that they do not need to be pruned. The second is that all brown growth should be trimmed away to encourage healthy regrowth. And the third is that grass trees tend to be in areas which have regular grass fires, and that they are healthier after being subjected to a grass fire. Because the third option isn’t that practical in many home location I tend to lean towards pruning back the brown growth as my prefer ed approach to grass tree pruning.

How long can grass trees live:

Most species of grass tree are extremely slow growing. Studies of some of species found that trunk height increases at about 1 cm to 6 cm per year, but this varies depending on growing conditions. In relative terms grass trees are often long-lived; some are even estimated to be up to 450 years old!

Grass trees problems:

Common pests to be mindful of with grass trees include, scale, mealybugs and bardi grubs. Common disease to be mindful of include root rot, foliage disease and anthracnose fungus.

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