Lavenders originate from the Mediterranean region. This includes the Middle East, Southern Europe, Northern Africa and many of the islands in and around the Mediterranean. Consequently they have adapted to fairly harsh and dry conditions. Also many of the soils in these areas, and parts of France and England where much of the early cultivation was done, have high a Calcium content. Calcium is a key secondary nutrient for plant development.
Various nutrients have different specialist functions.
Plants generally grow best when there is an ample supply of both primary and secondary nutrients. Some cannot grow if there is a deficiency of one or more of them. Other plants cannot grow if there is an imbalance between the nutrients, eg Grevilleas and Phosphorus. What this creates is ranges of plants that have adapted to specific soil types, and thus require modification of any soils into which they are planted. This is the case with Lavenders that have evolved on soils high in Magnesium and Calcium, having developed a need for greater amounts of both these nutrients than the average plant.