Wattle It Be? By Seed or Cuttings?

Tracey Perrott

Propagation of Australian wattles is traditionally done from seed, which is perfect for growing a huge range of Acacia species. Unfortunately seed propagation is not effective for selected cultivar forms, as seed from these plants is not always produced, and will rarely grow true to the parent.

The prostrate selection of Acacia baileyana is a great example of this, as some years it will set quite large amounts of seed, yet the resultant seedlings are usually upright and quite variable. This is where propagation needs to be by asexual means, such as cuttings, to maintain good selections with desirable flower and foliage colour, or growth habit. Growing acacias by cuttings is not hugely difficult if you have good material, and there are many species and forms that can be grown fairly easily in this way.

There are basic growing conditions that will make the job easier, although some experimentation will be needed to find the best method that works for you. Selection of cutting type, rooting hormone, hygiene, and date of taking cuttings, are other factors that may influence success or failure.

The main limiting factor is provision of ideal cutting material. By far the most consistant results are achieved from using container grown stock. This material tends to be less stressed, contains higher levels of plant nutrients and sugars; and is therefore able to sustain itself as a cutting much longer. By using healthy vigorous material, the cutting will have an extended life-span to survive until it is able to root and sustain itself.

Acacia 'Austraflora Cascade' Acacia 'Scarlet Blaze' Photos: Brian Walters

Acacia 'Austraflora Cascade' will strike reasonably well from cuttings off fresh young plants in pots, yet cuttings from garden grown plants may have a very high failure rate, and tend to drop all or most of its foliage.

The best material to use is fresh new growth that has just hardened off, with the stem still quite green and flexible. You can of course use garden grown material, but to maximise results you need to provide additional fertiliser and water so that it is growing very strongly. Keep in mind that new growth on larger plants that have not been recently pruned, (whether in ground or in pots), will be less successful than the fresh growth following a hard prune. Use of more juvenile material will always produce better results, and good success can be obtained with shoots cut off fresh tubed stock.

The cutting environment can vary depending on your region and the location of your propagation area. The ideal growing conditions include provision of misting, which is critical in the warmer weather, particularly with Acacia cognata varieties. However in cooler periods, it is helpful to be able to switch off the misting system. Rooting is enhanced with use of bottom heat, although this should not be above 20 degrees Celsius. Your propagation area should have medium light intensity, not located in full sun, nor completely heavy shade. Success is possible without the use of bottom heat and misting, but rooting will take longer, and cutting stress is more likely.

The propagation mix used with good success with most Acacia varieties consists of 10 parts propagating sand, 6 parts perlite, and 1 part peat.

Overall, good results are obtained using tip, stem, and heel cuttings of young material. Wounding can be beneficial, and some species respond well to foliage cutting to reduce evaporation, although others may react by dropping their leaves. If the tips are very soft, they are better removed to prevent leaf scorching.

A well known wattle is Acacia 'Scarlet Blaze', which must be grown by cuttings to maintain the stunning red wattle flowers. During propagation trials, this plant was found to strike well from very young soft material taken from igloo grown stock. The shoots have barely hardened off, and the long leaves are not cut back. Use of garden material can have a very high percentage of losses.

Most acacias will strike well with the use of IBA hormone rooting powder, at the strength of 1000 ppm, or 3000 ppm, for more mature new growth. Preliminary trials show some success with the use of IBA and NAA (1000/500 ppm) hormone combination rooting powder, and also with dipping in liquid hormones, at the medium softwood rate of 15 mls/litre. There is some indication that rooting would occur without the use of hormones, although the percentage struck is usually much lower. Acacias with grey or hairy foliage are better treated with 1000 ppm IBA powder, and not kept for long periods under mist.

The best time to take Acacia cuttings is when the material is really good, usually in late summer and early autumn. Most species can be propagated in January, February and March (under mist) with good results. Basic hygiene of using clean material and equipment, adequate cutting spacing in propagating pots/trays to maximise ventilation, and use of a fungicide post propagation time is beneficial.

Propagation of acacias is not highly technical. With the right material you can achieve good results with a wide range of garden cultivars. The following table lists some of the plants I have had most experience with. I hope this information encourages people to have a go at this wonderfully diverse group of plants.

From the newsletter of ASGAP's Acacia Study Group, March 2008.

Australian Plants online - 2008
Association of Societies for Growing Australian Plants