Once you attain the desired hue of blue, you need to determine what PH Level your soil currently has and you will need to re-apply your ammendments when new measurements show that the PH Level has become more alkaline. In between checks, you can probably add a smidgen (a tbsp or so) or once every week to 4 weeks (your choice). The "proper" amount is variable and is a function of many things, such as your geographic location, soil type (sandy, normal, clay), local weather (rainy, ...), etc. Increase the frequency and/or amount so it will yield the proper blue hues and maintain your soil Ph at the same level.

Luis