Growing Australian Trees

Australian Trees: Why not grow your own?

You may wonder why an article on Australian trees is smack in the middle of a Travel Blog?

Well I'm sure many travellers, like us, have an interest in native flora and we have often grown our own plants from seeds collected on our travels around Australia. Yes, it's a fairly loose connection but if you are not that interested you can always scroll on down or navigate around the article using the links in the side bar on the right. But for those still interested, please read on...

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As you travel across Australia in your Oka, you can't fail to notice that there are quite a few trees growing around the place. You may also have come across large areas where there are now none,  but there were some once, and where there could be a lot more in the future. Places such as the huge area of partly cleared scrub land in central Queensland or over-logged areas of Tassie.

You can't revegetate central Queensland, but you can help by growing tree seedlings for your own back yard or for friends and rellies. Many Australian trees grow quite tall so they need a lot of space but there are plenty of smaller varieties for average back yards.

Help is needed, it shouldn't be like this. This forest in north western Victoria seems to be missing something. You could see the wood for the trees here, if there were any.

Growing Australian native trees is easy and cheap, and a very rewarding past time. Its just the thing to take your mind off work (or that Oka problem) at the weekend and improve the environment at the same time. There are plenty of stimulating articles on native plants on the ABC's Gardening Australia site, and the Australian Native Plant Association has all the information you could ever need.

Greening Australia wants us to plant 1 billion trees by the year 2020 and I can’t do it all alone. At 10 trees a weekend it would take me 38 million years, but we can at least make a start. Australian natives are quick growing, very drought resistant and require no expensive fertilisers, in fact they hate fertilisers. That's why they've become weed trees in some countries (Israel and in California). It was interesting to see neatly manicured bottle brush (Callistemon) being used as street trees in Beverly Hills. Natives come in all shapes, sizes and colours for all types of environments from a small suburban backyard to a large scrub block.

Types to grow

Eucalypts, Acacias, Banksias, Hakeas, Callistemons and Melaleucas (paper barks) are the most common and easiest varieties to grow from seed yourself. Cuttings are rarely successful with natives without the use of exotic hormone treatments. You can even try desert oaks (Allocasuarina ) and native pines (Araucariaceae). They will germinate but they tend to need very deep sandy conditions to thrive away from their normal habitat. Likewise seeds from tropical areas may well germinate but not thrive in southern climates.

The best trees to grow are those already thriving in your area but seeds collected from any part of Australia can be germinated with a bit of care. The seed from most species can be collected at any time of year, except for acacias, since the seed pods/nuts don’t open while they are still on the tree. They only open when they have dried out, either through fire or death of the parent tree, and it’s easy to simulate these conditions.

Pick a handful of the older looking seed pods or gum nuts (the previous years are best) from a healthy growing part of the tree, not from the ground, and put them into a paper bag (not plastic) for a week or so on a window sill to dry out. (Keeping a few leaves and/or flowers as well will aid later identification). There is no need to heat or burn the seed pods (except banksias) and after a few days the valves will have opened and the seed can be shaken out.

Banksia nuts can be dried in an oven or on the BBQ, simulating a bushfire, until they open and the seeds drop out.

Acacia seeds are much larger and black and if you miss the pod's ripening/opening period, they can usually be picked up off the ground a few weeks after flowering, before the ants carry them all away.

Germinating the Seedlings

With some exceptions, such as Tasmanian Blue Gum (E. Globulus) and Mountain Ash (E. Regnans) which naturally grow in wet boggy conditions, Australian natives prefer light well drained soil but are usually quite adaptable. Seedlings of all types will germinate adequately in standard Woolies or K-Mart potting mix (which are the cheapest), mixed with some dry sand.

Most Australian plants are designed to survive in conditions of extreme heat and drought so they generally grow very long roots which do not like being disturbed. So although they will germinate, growing them in small flower pots is not ultimately successful, as the roots will curl around the pot and stunt their growth. For this reason, never buy tall natives in small pots from nurseries.

I have found that the humble 1 litre cardboard milk carton (or similar) has all the necessary attributes for raising seedlings. They are tall so seedlings can develop long roots; they are biodegradable (the thin plastic outer coating keeps them together just long enough before it rots); they are square so they stack together well, and most importantly they’re free. Obviously 2 litre cartons can be used but require a lot more potting mix. 

Don’t cut the tops off, just open them out square so they remain as tall as possible and punch 2 or 3 drainage holes in the base. Seeds of natives can be sown at any time of year but will grow fastest through the warmer months. Thoroughly wet the potting mix (use wetting agent) in the milk cartons before sowing. Most native’s seed is very fine and can be mixed with dry sand for ease of distribution. Sprinkle the seed sparsely on the top of the potting mix and cover with a thin layer of seed raising mixture or fine potting mix. Water gently with a fine mist spray and keep moist.

Acacia seeds have a very hard coating which can be softened by dropping them into a cup of boiling water for a few hours before sowing. It won't harm them.

Place a sheet of glass over the containers to keep them moist and keep them in the shade until they germinate, which will take one to three weeks depending on the variety. Remove the glass after germination, as they can withstand full sun as soon as they germinate, move into full sun and keep the emerging seedlings moist. If kept in the shade after germination they will quickly grow tall and lanky.

When they have 2 or 3 sets of leaves and are around 3-5 cm high (their roots will be twice that length), thin them out to one strong seedling per container. Transplanting small seedlings is possible but not always successful due to their long roots. To try this and avoid wasting seedlings, cut the potting mix containing the seedling into a block around 2o mm square and as deep as possible using a long knife or chisel and carefully move to a new container. This often works but don't disturb the soil around the roots, which will be surprisingly long. Water in well and refill the "hole" left in the original container with new potting mix.

Franklin Riverside, Tasmania

Planting out

The best time for planting out is at the end of the dry season just after the first heavy rains. In Adelaide this means planting out between May and July unless you can guarantee water to the young seedlings through the hot dry periods. Any later and the trees may not generate sufficient root growth to survive the long hot summer.

Where you can provide regular attention, seedlings can be planted out when they are around 10 to 20 cm tall. If they have to fend for themselves, they should be left in their milk cartons until they are around 30 cm tall, but no more or the roots will bind around inside the container. Deep holes are best with some but mulch to keep the moisture in.

You can plant them still in the milk cartons if you like, but I usually remove the (now rotting) plastic outer shell so I can check on the root growth and straighten them out a bit if necessary but don't disturb the root ball too much. Provide protection against wind,  rabbits and sheep in country areas. I usually stake them loosely, partly for support but mostly so I can find them again after the long winter grass has grown.

Watching them Grow

Australian natives require very little attention after germination except to keep them watered, weeded and in full sun. Snails and caterpillars can be a pest but natives are quite resilient and healthy seedlings will regrow even after being badly eaten by insects. Where necessary, chemical sprays will fix the problem, but will kill all other life forms as well.

You can grow the seeds from Grass Trees but they do take 20 years to grow 20 cm. These in the Warumbungles are hundreds of years old.

I have raised over 500 native seedlings of 50 different varieties this way over the last 10-20 years with around a 95% success rate and most are now approaching maturity. 10 acres of our 20 acre block now has  a good covering of native vegetation (including a lot of feral olives), where there was none when we moved in. You can take a closer look in Google Earth at these coordinates, 34° 45.655'S, 138° 42.421'E.

Our block is outlined in white. rural living but close (too close) to "all facilities". The lower 10 acres and the area around the house have been planted with home grown seedlings. The central area is a bushfire buffer zone kept clear by neighbours sheep, in theory. It's too steep to slash.

The "Men of the Trees" or "Trees for Life" organisations in each state can provide seed distribution and tree growing kits for a small annual membership fee, to help people get started.

Growing trees is a rewarding past time which is cheap and satisfying as well as ecologically sound. I recommend it to everyone.

© 2011 David Ribbans