Mammillaria bloom encourage

Greetings to all mammillaria growers!
I got two small mazatlanensis seedlings in 2011. They have been growing quite all right so far (into a solitary and bushy forms). But I haven't got them bloom yet. Are there any actions I can do to encourage them bloom? I've got some other species (boolii, fraileana, sheldonii) that show their beautiful flowering on a regular basis located on the same spot. There are some other (pretty mature) plants unwilling to bloom (microcarpa, candida); do these ones have something in common concerning their cultivation?
Would be happy to get any tips!
Oleg

Not sure it will help but: a drought stress (a dry winter) usually helps my Mammmillarias to bloom.

THis is a common question, but the answers can be quite varied. At the moment I have boolii and its ilk flowering well, and the grahamii, sheldoniii, mazatlanensis complex also coming into flower. I don't feed them much, but they do get good winter light.So my recommendation would be dry them off in early October, keep them cool,over winter (4-5C) in good light, restart watering (small amount at first) and in late June onwards you shoud get them into flower. I water about every three weeks, and sometimes a good drench can give them a kick into flower too.

There were somr flower buds on my mazatlanensis plants, but they were not opening, we had 9 days holiday and they didnt receive any water in that time. After i came back to work, i gave them plenty of water and the buds started to develop.
These flower photos are from 9th of june.

Yes, watering after a period of dryness can promote flowering. It's one reason I don't water too frequently.its like the plant says to itself "at last, food! Now I can become fertile as there will be water for my baby seeds".

As I am in Brazil, my winter is not really cold (it is cooler than summer, nights are cold, but seldon below 12 degrees Celsius). Nevertheless, I keep my Mammillarias dry during winter. I start the dry period in late Autumm (May 15th) and they keep completely dry until early/midle winter (August 1st) (late winter is already too hot and I cant wait until spring).

As a result I have many flowers , even before resume waterings. Many species such as M. pectinifera, lasiacantha, mercadensis, brachytrichion, meissnerii, dixantocentron, longiflora, leptacantha, sinistrohamatha, pseudocrucigera, are in bloom curently in July (winter) (they are without water since May 15th).

Other species will bloom after I resume watering such as longimamma, candida and others I cant recall now.

My doubt now is: when is the best time to resume waterings? Is it better to give them a shorter dry period (30 - 45 days) , or a longer one (60 -75 days)? I presume that probably 30-45 days would be sufficient to induce flowering and they would benefit from receive watering earlier...so they can produce more flowers... however, considering the number of plants in bloom now, totaly dry, maybe this long period of drought is benefical for Mammillarias to bloom. So I never know when to resume waterings.