One of the most promising new seed treatments we’ve been trialling for Acacia species, such as Acacia phlebophylla and Acacia obtusifolia, 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 but longer times would be expected for alpine species. 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.
Acacia obtusifolia seeds started germinating in the fridge within 2 weeks and were removed and sown as normal. Healthy seedlings have developed and are doing very well. Acacia phlebophylla seeds did not germinate in the fridge within the time limits of this trial. The seeds were planted out as normal after the chilling time and in comparison to a control, double the number of healthy seedlings have appeared, especially after more subsequent nights under 5ºC and warm days up to 20ºC.
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.