Question
For postharvest treatment of lisianthus by the grower, is it useful to use 200 ppm aluminium sulphate plus hypochlorite or is either one adequate on its own to be added to the 3% sucrose? Should the pH of the solution be reduced to around 3.5 using citric acid or is this not necessary?
Answer
We didn't test the different combinations of materials that you are asking about. However, I tend to avoid combining bleach and sugar, since I imagine that the sugar will quickly reduce the hypochlorite present in the solution. Aluminium sulphate forms flocculent hydrdoxide precipitates that trap bugs and dust, and this is the major basis of its action. In addition its hydrolysis reduces the pH which also has a biocidal effect. Acidification seems to be most important with woody stems (roses, lilac, etc.), and you have to be careful combining citric acid and aluminum sulfate since the acid can solubilize the aluminum ions and cause aluminum toxicity (I think that this has been reported in chrysanthemums). As I look at our data, I think that 1.5% sugar is adequate, since it provides most of the carbohydrate benefit and is certainly cheaper than 3%. --Michael Reid