Thursday, May 5, 2011

Kurrajong - The Perfect Shade Tree

Brachychiton populneus
Family: STERCULIACEAE
Kurrajongs are dry rainforest trees which take the “dry” more literally than most. We see them far out on the western plans, as in this specimen in a Western Downs town which is doing such a good job of shading a cool Queensland-style house.

Their deep roots help them survive droughts. Deep roots also mean (as with other dry rainforest trees) they are less likely to create problems for buildings and other structures. However the roots do seek water, so should not be planted closer than 3.5m to water pipes or sewage lines.


Another part of the secret of kurrajongs’ drought survival is the capacity to drop their leaves in dry winters. The degree of leaf drop depends heavily on the availability of soil moisture, so in wet winters they may lose very few of them. This photo was taken near Toowoomba in June 2008, which was probably the driest of all the dry times in our recent long drought.




The species can grow tall, as shown in this bushland example, also near Toowoomba. Usually, rainforest species only grow this shape if surrounded by other trees. It is possible that this very old tree spent its youth in a quite different environment from the grassy eucalypt woodland you can see in this modern photo. A great deal of such country, along the Great Dividing Range and the valleys to the west of it, was once dry rainforest. It was cleared so long ago that we have forgotten it was ever there. The shape of this tree may indicate that this was the case here.


Kurrajongs have a very pretty flower, and unlike some of the other Brachychiton species (notably the flame tree Brachychiton acerifolius), they don’t link flowering with leaflessness.
This photo was taken in October, and the tree had a shady green canopy.
While mature trees can put out a great show of flowers, it won’t happen every year, so the kurrajong’s ornamental qualities are largely based on its cool green canopy.


As with many Australian trees, their juvenile leaves differ from the leaves on older trees. These leaves are from a very young tree.









The shape on the right is the one we most commonly see, while the one on the left only occurs on mature trees.








I photographed this paddock of kurrajongs at Gilgandra. They were neatly pruned, and I wondered why. Then we drove on to visit the Dubbo Western Plains Zoo, where we watched giraffes being fed with kurrajong leaves. No doubt this explained the mystery!

The photo is such a good demonstration of the results that we can get from pruning most of our dry rainforest tree species. You can see how well these Australian native trees would grace a formal garden. They can be kept to a size suitable for the suburbs, and make very good street trees, as seen in Goondiwindi.




This young kurrajong in Crows Nest is being groomed for the job.









Pastoralists have long recognised the value of kurrajong leaves as emergency drought fodder for their stock. Unfortunately they have all too often solved their problem by cutting down whole trees, a curiously short-sighted solution. The result is that, while we see many young trees in the Toowoomba district, large, old ones are rare.


Kurrajongs are host trees for one of our larger butterflies, the tailed emperor (Polyura pyrrhus sempronius). We caught this delightful pair “kissing” in the bushes at Kwiambul National Park last weekend. (Butterflies kiss with their antennae.)


Brachychitons are recognised as being fire resistant. A row of them on a fenceline downhill from the house, in bushfire-prone areas, could make all the difference (though of course no tree will resist a very large bushfire). A green canopy catches sparks, and might just be the factor that saves a house from catching alight.
A “home among the kurrajongs” is a very Australian image, and considerably safer than the one among the gum trees which is celebrated in the well-known song.
Kurrajongs can be transplanted at up to 8 years old.

18 comments:

Stan Lusby said...

Thanks for the info. I witnessed Kurrajong in the drought of 1966. I had only been in the country for five weeks as a young immigrant surveyor and wondered then why they were not used in swathes as fire retardant protection for human settlements against the eucalypt killer fires like you have in NSW at the moment.

"Ignorance is not lack of knowledge but the mischievous desire to ignore."

Stan Lusby
Hsven Street
Moeraki
South Island NZ

Patricia Gardner said...

Hi Stan.
I am interested to hear your point of view. This is certainly a tree that performs well in the drought.
We do see Brachychitons used as minor firebreaks far more than you would have seen in here in 1966.
The problem with them is that they are not useful, in enough other ways, for it to be regarded as financially viable to sacrifice the amount of land that would be needed for firebreaks on a scale would have any effect on the kind of fire they're having in NSW at present. A hot fire in Eucalyptus country can jump many kilometres through the air to another stand of eucalypts. One would need great, long belts of kurrajongs many kilometres wide - not really a practical proposition.
A nice thought, though.
Cheers,
Trish

Anonymous said...

Hi Trish
I am planning to grow kurrajongs as an ember catch break around our house in the Adelaide Hills. Can the kurrajong tolerate frosts?
Thanks in advance.
Jules

Patricia Gardner said...

Hi Jules.
They are said to be able to tolerate frosts to at least -5°C.
do you know how cold your frosts are?
If you haven't already done it, next winter you might like to leave a maximum-minimum thermometer outside overnight in winter, in selected places (on a stake so it sits a few inches above the ground).
there are always quite wide variations in the temperatures around any given site, depending on the degree of slope and the amount of shelter. It is likely even to include some frost-free spots. Knowing your frosts can be a useful tool in choosing the right plants for the right places.
Of course another way of discovering whether a plant is likely to survive in your area is to find out if it grows naturally there. Choose a site with similar slope, aspect and degree of shelter, and Bob's your uncle!
Here's hooping Kurrajongs work for you!
Cheers,
Trish

margy.gill said...

We have a currajong in our front yard and love it. One problem is it drops a huge amount of sap which sometimes looks like rain and is very sticky. I assume it is because of the lack of rain. Is there anything we can do about it?

Patricia Gardner said...

Hi Margy.
Nice to hear from you.
I'm afraid I can't offer you any instant solution for the sap problem, which is not one I have come across, with kurrajongs.
Sticky sap is usually a sign of plant damage. Are you able to track down where it is coming from?
Is it an old tree?
Trish

Anne E said...

Hi, just had many ladies to my garden for a monthly garden club meeting. Many said the name of my unknown tree was a Kurrajong tree. However after reading and looking at google entries I'm not so sure. The tree has 3 prongs like the pictures, but it certainly doesn't tower. Do you think it could still be a Kurrajong?
Anne O'Brien
Toowoomba

Patricia Gardner said...

Hi Anne,
Kurrajongs don't necessarily "tower". The street trees in Goondiwindi are quite small, despite apparently being old. The problem with tree height is that tree size varies with the soil and available water, but especially according to what is growing around them. They stretch tall if they need to compete with other trees for light, but stay low, broad and compact if they're getting plenty of sunshine. Kurrajongs (like bottle trees) are particular prone to this variability.
I find internet statements about the height of trees sometimes irritating. The writers seem to want to boast that they've found another even taller one, which was probably in a gully in a forest somewhere, stretching to match the canopy on the nearby hillside. The height may even have been a historic record, from the days when Australia had rather more in the way of forests and old trees.
The same plant in a garden might be a happy, healthy tree which reaches its maximum at a third or even a quarter of the claimed height. These extreme height descriptions do put people off planting them in their gardens, which is a pity. If we're growing a plant in a garden, we don't want to know the record height. We want to know what it's likely to do in a garden.
Better understandings of the likely height of garden plants come from plants which have grown in the open since they were tiny, such as those in streets, parks, and gardens.
The first photo in my article shows a huge tree in a garden in Millmerran. I have only ever seen another one of similar size that I could be reasonably sure was a planted specimen. (It is in the Helidon State School grounds) I suspect it would take 100 years or so to reach this kind of size.
The other characteristic which helps identify kurrajongs is the rather soft wood. As with bottle trees and flame trees, they sound a bit hollow if you knock on the trunk. It hardly even counts as timber, being the kind of thing cattle can eat. You wouldn't want children to climb any of these trees, as the branches would break fairly easily.
Hope this helps.
Trish

Robyn Bird said...

How long does it take a Kurrajong Tree to mature?
I'm really interested to plant more because I like the comment about them being fire resistant. i live on a bush block in a fire prone area.

Patricia Gardner said...

Hi Robyn.
The question is difficult to answer, as like so many "dry rainforest" type trees, kurrajongs are capable of being slow to the point of seeming to hibernate, or quite fast, depending on conditions.
For fast growth, they need to be kept moist in the root zone, (meaning the soil deeper than about 15 centimetres). The less water you waste on the surface, where most will be lost to evaporation, the better.
The soil moisture levels in much of the local region are perfect for planting right now, after the good rain. And to plant while the weather is still quite hot gives the little plants a reasonably long first growing season before winter sets in.
In drier times I have had excellent results from burying a large plastic bottle with a hole in the bottom beside each of my small trees, and filling them with water as often as possible for their first season. This wasn't with kurrajongs but with another dry rainforest species, but I think the effect would be much the same.
It's important to keep grass well away from all young trees, of course, and a layer of mulch both helps keep soil moisture in, and encourages healthy soil fungi which can make all the difference to young trees.
I think kurrajongs are a great choice for fire-prone areas. All species of dry rainforest-type trees are pretty good for this, too, so they're the sort of thing to look at if you want some variety.
Eucalypts and pine trees are the high fire risk plants, so are best avoided where fires might be a problem.
Cheers,
Trish

Anonymous said...

Hi Trish. I live in Mackay, Qld. I have two Poinciana's which unfortunately have to be removed due to root systems causing damage to the house so I am looking for a shade tree to replace them. Would the brachychiton populneus grow well here do uou think? And is the root systen invasive? Thanks, Toni

Patricia Gardner said...

Hi Toni.
I suspect kurrajongs wouldn't be very happy in your coastal climate. I can't remember seeing them when I was up there, and I think it would be too damp for them.
There are a lot of lovely shade trees native to your local area, which might suit your purposes better. I think you could probably get some good ideas and advice from the rather wonderful botanic garden you have there in Mackay.
There are also some very good books on tropical gardening. such as "Across the Top. Gardening with Australian plants in the tropics" by Keith Townsend, and others. You could try the shop at the botanic gardens, and maybe bookstores in town, for them.
Hope you find something wonderful to grow.
Cheers,
Trish

Tim Allen said...

Hi thanks for all this great info . I live on the coast the soil type is sand and ph level is 8.0 , do you think a
Kurrajong would be suitable ? . many thanks.

Patricia Gardner said...

Hi Tim,
The pH shouldn't be a problem, but the sandy soil might, and kurrajongs might also dislike the humidity of a coastal climate. This is a plant that likes its air dry.
There's nothing to stop you giving it a go, but it may be a long-term disappointment.
I am a person who loves to see plants growing in their own place in the world, where they participate actively in the web of life we call "the ecology". I would suggest that you think of exploring your local native flora for something else that might suit you better.
Australians are often surprised at just how rich their local plant diversity can be, once they start investigating. The result, should you choose this option, is a plant which loves to grow at your place. Robust good health always makes a plant more beautiful, and as a bonus, you get a plant that isn't an ecological "passenger".
Cheers,
Trish

Ed said...

I live in Tucson,AZ USA and the local nurseries here are selling these. I bought 10 of them that were already 5 years old. I've noticed on one of them that the leaves are a little wilty. I'm suspecting it's from lack of water. As soon as they were planted I watered them with drip emitters with 24 gallons of water each day for a week. Then I taperered off to every other day. 9 of them are doing great, but one of them is larger and showing wilty leaves. I'm watering that one every day still to see if that's the reason.

Patricia Gardner said...

Nice to hear from you, Ed
Are these plants in pots?
As you would have gathered from my blog, my experience is with growing them in their own native range, and of course we only grow them in the ground,where they flourish through our worst droughts. I have never seen them grown in pots.They have a large tuberous root, and I can't imagine that they would take very happily to long term pot culture. Deformed roots might make them prone to disease.
They would also hate to be overwatered, and could suffer from fungal diseases as a result.
However, it sounds as though yours are soldiering on despite their less than optimal conditions. Long may they continue!
Cheers,
Trish

Carolyn said...

My trees are planted with grass surrounding them. I am trying to water my grass and not over water the trees. The trees are losing leafs at a rapid rate and I think this is not good. Please help me!

Thanks,

Carolyn

Patricia Gardner said...

Hello Carolyn,
You don't say where in the world you are, so although you are writing in June I have no idea whether you are in early winter (southern hemisphere) or early summer (northern Hemisphere)
It is normal for kurrajongs to drop their leaves in early summer.
They don't do it every year, and sometimes the leaf-drop is only partial. Sometimes it is more complete. It usually means that the tree is going to flower (something they also don't do every year). If the flowers are pollinated, they will then produce seeds, which you can grow, to make more trees. If you do this, check the roots as they grow to make sure they have enough room in the pot. Kurrajong seedlings have a large tap-root like a fat carrot, and need plenty of room for it.
You can also eat the seeds (lightly roasted) or make a coffee-like drink with them, but make sure that you rub the seeds well (with gloves on) to get rid of their hairy little coats. Those little hairs are prickly and will leave tiny prickles in your mouth!
Don't worry that you might be over-watering the ground your tree, unless your soil is rather soggy or swampy. Kurrajongs are very tolerant, and happy to be given some water if the soil drains well, especially when they are making new leaf after a leaf-drop.
Let me know how it goes after a few months.
Cheers,
Trish