Mindmaze,
From the website link you provided...
"The differences, however, between different kinds of laterite are very big. Not every red soil constitutes laterite and by far not every laterite is suitable for aquaristic conditions.
The degree of oxidisation of the different kinds of laterite varies a lot as well. Laterite can be so 'stony' that plant roots are incapable of dissolving iron and other nutrients from it. When searching for the right laterite one therefore has to look out for a specific grain structure of the laterite. Furthermore, the chemical composition of laterite also has to be checked and tuned exactly to the requirements of the aquarium. Important in this context, too, is the correct chemical balance between iron and the remaining trace elements, e.g. manganese, zinc, tin, copper as well as the important macro nutrients such as calcium, magnesium and potassium. The pH-value has to be right as well."
So if you really want to use the stuff in your backyard, I would suggest doing a chemical analysis before testing on your plants. Otherwise, your plants might die.