Xanthorrhoea johnsonii is one of 28 species of grass trees in Australia. They have a trunk that is typically black as a result of bush fires, hence the nickname “Blackboy”.
Grass trees are extremely hardy IF well cared for in the initial stages of transplanting from the wild. Only a small number of reputable companies successfully transplant grass trees. It can be difficult to see whether a tree has been correctly transplanted for many months until their reserves are slowly depleted. Our trees stay here in the nursery until they display strong root growth and significant new top growth. This can range from 4 months to several years. We will only sell them once we are completely satisfied that they have successfully survived the traumatic transplant process and while they are healthy and actively growing. This is why we have the reputation for quality.
In poor bush soil the trunk of a grass tree will grow approx 9mm per year. A tree with a metre high trunk could be 100 years old. In better soils, growth can be faster and trees are more likely to grow multiple heads.
Xanthorrhoea johnsonii are typically single trunked specimens that grow up to 5 metres tall. Minor changes in their trunk direction are usually caused by new growth after the tree flowers. Major bends or multiple heads in the the trunk of a grass tree can be caused by accidents – eg another tree falling on to the apex or pushing the grass tree over. Usually it will attempt to continue growing vertically. Every tree is unique and has years of history reflected in its shape.
Your tree may have hard lumps of resin near its base. During bushfires, the intense heat melts the natural resin in the trunk and this oozes out and solidifies. 100 years ago this resin was extracted and used as gunpowder, in shellac, and as a source of phenols. It is still being used to stain timber.
To establish your newly planted grass tree as well as possible, we suggest the following advice.
1. Proper drainage is very important. If you are unsure if your soil drains well enough, dig a decent hole where you plan to plant the tree and fill it with water 2 days in a row to simulate lots of rain. If the water drains away, then you’re fine. If the water does not drain away or you have heavy clay soil, create a drainage solution, like raised bed of soil.
2. Disturb the roots as little as possible. Rather than pulling or rolling the tree to get it loose from the pot, try gently laying the tree over. Cut the base of the pot off and carefully place the tree in a hole which is larger than the root ball. Cut up the side of the pot and lift away from the root ball. Do not disturb the roots.
3. Back fill the hole around the roots firmly with a well draining soil mix, and water in well. Trees need to be firm. If they are tall and unstable they may need propping until roots grow more extensively.
4. Water in well. Until the roots are established (at least 12 months) your tree will need a regular deep watering. Maximum once a week during hot, dry periods. Less often in cooler, wetter times of the year.
5. Fertilise with a seaweed fertiliser. Monthly doses of a seaweed fertiliser will keep the tree nutritionally healthy and promote root growth in the initial stages after planting.
6. Feed with a slow release fertilizer for natives, especially during flowering.
7. Keep mulch back at least 15cm from the base of the trunk to avoid rot.
Once established and growing vigorously, our grass trees are maintenance-free. Although, like anything, they don’t mind a drink when it gets really dry.
Caring for potted grass trees
Feed with about 30ml of slow release Osmocote for natives in Spring & Autumn. Remove the flower spike to encourage continuous growth, or be prepared to sit out its dormant period (See the section about Flowering below).
About once a month, to maintain the health of your tree while it stays in its pot:
1. Spray the leaves with seaweed solution & add 2 cupfuls to the pot (water in lightly).
2. Keep an eye out for scale (especially during Autumn and Winter) and treat the leaves by spraying with white oil.
3. Whenever you can’t find any moisture 5 cm deep, give it a thorough watering. Allow the top 5 cm of soil to dry out and don’t use a saucer except perhaps for short periods of time in very hot, dry conditions.
In the wild it is rare for a tree under 800mm to produce a flower spike. However, In good soil and growing conditions, they can flower sooner and even produce more than one spike, which may then develop into more heads. Look out for a grub that bores into the spike and into the heart of the tree. If you see that a grub has bored into the flower spike, remove the spike by cutting or snapping it towards to bottom of the spike. Then treat with a pyrethrin spray.
If there is no grub in your flower spike, there is no need to manually remove it. We encourage you to let nature take it’s course. It will fall or be blown over eventually.
As the flower spike is the active growth point for the tree, after flowering, it is natural for the tree to remain dormant and not produce new leaves for months or even years. DO NOT PANIC. Don’t over water or over fertilise as no assistance is needed. Just be patient. Your tree has already survived for a long time often by shutting down like this for long periods. Burning the old growth in spring or summer can sometimes encourage your tree out of dormancy. If you would like to encourage continuous growth and avoid the tree going dormant, you can remove the flower spike as soon as it appears and feed the leaves and roots with seaweed fertilisers. But dormancy is not to be feared. It’s a normal protection mechanism.
Brown outer leaves are normal, but if the ends of the new green leaves are going brown, the soil is too dry.
Loose trees should be stayed until established and stable.
Keep a look out for scale (spray with white oil and rub leaves together).
Keep debris out of leaves to prevent fungal attack.
Look out for grubs in flower spike (see above – “Flowering”).
Trim or burn the old leaves to keep a ‘maintained’ look if desired.