Cactus soil and fertilizing

Although cactus are plants that grow naturally in very poor soils, they do better if growed in a soil with more nutrients.
There are many cactus mix formulas which are good for growing cactus, but many have ingredients in their formula which are difficult to obtain.
There is a big diversity of soil needs within the Cactus family. However, after seeing them growing well in different kinds of soil, we conclude that we can set a soil formula adapted for the majority, adjusting this formulas to each particular species need.
We are going to name standard mix, to the general use soil mix.
This mix must have all the conditions that are essential for a cactus soil; porosity, moderate nutrients, and medium water retention. Several kinds of formulas could be given if we are guided by the previous conditions. A good start would be a soil made up of four parts of coarse sand or gravel (particles of between 3 and 4 mm.) and 2 parts of potting mix.
Adjustment of these mix is made by adding more coarse sand/gravel or more potting soil, depending on each species particular need.
Fertilizing of the standard mix can be made by adding a spoonful of bone meal by liter of mix. This way, we do not need to fertilize again until the next pot change.
Fertilizers with high proportion of nitrogen on its formula must be avoided in cactus, since they cause weak and fleshy tissue growing, as well as a diminish of the number of produced flowers or even their appearance.