Acacia phlebophylla, a type of acacia also known by the names Buffalo Sallow Wattle and Mountain Buffalo Wattle, is a straggling shrub to small, twisted tree reaching up to 5 m in height. It is a close relative of Acacia alpina.It has large, elliptic, flat, commonly asymmetrical phyllodes 4–14 cm long, 1.5–6 cm wide, with coarse veins, a leathery feel, prominent nerves and reticulated veins. Deep yellow rod-like flowers appear in spring (June–December in Australia), widely scattered on spikes 4–7 cm long, followed by 7–10 cm long legumes in November–March, narrow, straight or slightly curved, releasing 5-10 elliptical seeds, 5-7.5 mm long. Solitary or twinned spikes, to 6 cm long. Only known from the high altitude granite slopes of Mount Buffalo National Park, Victoria, Australia, where it occurs above 350 meters in woodlands and heathland often amongst granite boulders (From Wikipedia)
For many years this species has been regarded as being extremely difficult to establish outside its native range and in cultivation. Several cultivation attempts using different media and even tissue culture have failed dismally. I assumed that the degree of difficulty in establishing this species in cultivation may have been due one of two factors; unable to replicate native climatic conditions (although A. phlebophylla would be assumed to be quite resilient as it clings to a mountain side and can be subject to very high and very low, even snowy conditions at times of the year) or the lack of a rhizobial bacteria or mycorrhizal fungi symbiont that is important or critical to their well being.
Mycorrhiza are fungi that live in the soil, or within plant roots, that form a mutualistic relationship with the plant, allowing the plant greater access to nutrients and water and in return the fungi receives carbohydrates. More info here : http://en.wikipedia.org/wiki/Mycorrhiza
Rhizobial bacteria live in the soil and can take up residence in special root nodules that are unique to those in the legume family and include Acacia, Soybean, Bean, Pea amongst thousands of important crops. More info here: http://en.wikipedia.org/wiki/Rhizobia
I tried a few batches of seed I had received as a gift with different treatments. With limited success simply subjecting the seeds to hot water treatment gave a few seedlings with varying survival, most not living very long. Hot water treatment and mycorrhizal fungal treatment provided similar results. Hot water treatment and a commercial Acacia rhizobia inoculant provided good germination over a period of 6 months (this is normal i find with A. phlebophylla, seeds can lay in the soil untouched by insects or bacteria, fully imbibed with water, simply waiting for an external trigger, which I often found to be a good thunderstorm event). From germination onwards the seedlings were strong and healthy and have continued to grow well under 50% shade conditions in SE QLD Australia, summer 2013-2014, a particularly hot and low rainfall summer so far.
The inoculant was supplied by Becker-Underwood, and when I recently tried to purchase more was told that they had ceased to make this particular inoculant. More searching and it looks as though no one in Australia is now making an inoculant for Acacia, which does sound as ridiculous as it is. Luckily, Acacia phlebophylla does not appear to be worried about having a particular rhizobia and a promiscuous species or mixed strain inoculant can do the job.
For the trial the seeds were prepared as follows: subject to hot water treatment (boil kettle and pour just boiled water over seeds and let stand overnight), slurry of inoculant was applied to seeds and once seeds were planted, they were watered in with remaining inoculant slurry, which is often called inoculation by soil enrichment. Once seedlings emerged, they were mulched with a 7mm basalt gravel and this appears to help them by stopping moss growth and perhaps providing micro nutrients. It’s also aesthetic!
Whilst it is as simple as it sounds, I hope this technique enables this important species to be grown more widely in different parts of Australia. It is probably the most beautiful Acacia I have seen, especially in habitat.
Potting media for Acacia phlebophylla
We’ve settled on the following potting mix for Acacia phlebophylla:
- 30% washed coarse sand
- 30% pumice 1-4mm
- 20% fine coco peat
- 10% blue metal granite gravel 5-7mm
- 10% medium perlite
Fertilising Acacia phlebophylla
Acacia phlebophylla can be fertilised from very early on and it appears to be of benefit to the young seedlings, especially before they may have made a relationship with rhizobia. It may actually increase the biological activity of the potting media and enhance uptake of a rhizobia by directly feeding the soil life. We suggest fertilising with either an Australian native slow release fertiliser or an organic well rounded fertiliser. Fertilise sparingly initially and at probably 1/4 – ½ strength.
Update 3/3/2014: The seedlings are progressing well and a few have been sent out to growers around the country. No losses in the nursery so far. I have noticed they benefit at this stage by going into a more open position, 100% sun for at least a few hours per day. The root system is well established in the plants pictured in pots above, many nodules were observed on the roots and the typical sharp/vinegar smell associated with rhizobia bacteria was present. A notable feature was the absence of a tap root on the ones I have sent. This could be advantageous to this species being kept in pot culture as a tap root is not a benefit and the longevity could be maintained without the need to be planted out. Living on the side of a granite mountain, Acacia phlebophylla would benefit from a branching root system with no central tap root, a strong rhizobial partnership and most likely a mycorrhizal association for added nutrient and water uptake.
Update 17/7/2018: Its been four years since this post about Acacia phlebophylla seed germination and cultivation; time for an update! Over the past few years I have been experimenting with some new techniques for germinating this species. One of the most promising is a cold stratification of the hot water treated seeds. Being a sub-alpine species, Acacia phlebophylla does appear to benefit from a cold stratification period subsequent to hot water treatment. This is typical of many alpine and sub-alpine species. Seeds were hot water treated (kettle boiled and water poured over seeds and allowed to soak for an hour. Seeds were then put into a ziplock bag with moist coco peat and placed into a normal fridge for a period of time or until germination was noted to have taken place. A chilling time frame of between 500-1000hrs @ 5ºC was the limit of this particular experiment. Seeds were then removed and sown as normal. Seeds have been germinating erratically over the last 2 months but it appears the cold stratification has helped significantly. Especially after more subsequent nights under 5ºC and warm days up to 20ºC. In comparison to a control, double the number have germinated and emerged.
More trials are needed. Another method used to overcome cold requirements is the use of gibberellic acid (GA3) in various concentrations and in conjunction with or instead of cold stratification. These will be the subject of future trials.