Maybe you remember? Last year a number of AquaMinerals staff members tested the use of aluminium coagulation sludge for the blue colouration of hydrangeas in their own gardens. And it worked. Time for a follow-up.
Since the hydrangea growing season and colouration begins in September, we’re taking advantage of this moment to carry out a pot test. Over the next four months, working with a blue hortensia nursery, we’ll be studying whether, and under what (real) conditions, the blue colouration occurs. We’ll use sludge from many drinking water locations, and vary the composition and dosages in tests on several (potentially) blue species. In addition, we’ll examine whether humic acids from drinking water production support the blue colouration process; after all, we know from other research that the same humic acids provide for a better uptake of aquafer (and therefore probably do the same for aluminium). We will then compare the results against the control group.
What we know already
The release of aluminium and its uptake by the plant is decisive. It is a possible that coagulation sludge is a slow-release substance. The question is how quickly the aluminium is converted in the pot’s (acidic) environment. An overly rapid release will poison the plant, while an overly slow one will result in rose flowers. Other factors that can affect the colouration include the accessibility through the roots, the presence of iron/lime and the fertilisation.
We hope that the tests will demonstrate that there is an impact, so that we can then proceed with targeted follow-up research. It is possible that the sludge could replace the current ‘blueing agent’ (aluminium sulphide and potassium alum from the mining/chemical sector) used by professional growers and consumers.