http://www.pwilson.demon.co.uk
Phil Wilson mentions 'tufa' as a ping substrate. Just click 'cultivation,' then 'growing Pinguicula.' Tufa is defined as 'the calcerous and silicaceous rock deposits of springs, lakes, or ground water;' also, tuff, 'a rock composed of compacted volcanic ash varying in size from fine sand to coarse gravel.'
My current Mexican ping mix is 1:1:1:1 peat/sand/perlite/vermiculite. To this I add a bit (pinches) each of dolomitic limestone and gypsum. I do not use chalk.
I DO fertilize them: Epiphytes Delight at 25% misted onto their foliage once monthly.
About lime...the June '02 CPN, p61, has an old quote from Joe Mazrimas: "...I noticed a dramatic improvement in the growth and flowering of Mexican
Pinguicula after a one-time watering of lime water. A thimbleful of hydrated agricultural lime was added to a pint of deionized water and shaken vigorously for two minutes. A cupful was poured into each pot and I tried to avoid splashing any on the plant leaves. Most of the plants are growing in an even mixture of perlite and living sphagnum moss. I continued to water them with deionized water and I noticed a rapid spurt of growth after about 3-4 weeks followed by the production of many flower spikes."
Intrigued, I quickly watered a couple expendable P. moranensis and P. agnata x gypsicola with lime water. We'll see what happens a month from now!
BTW, Tony, I have my N. northiana in 2:1:1:1 vermiculite/perlite/sand/lava rock. Perhaps I should change it next time I repot...what would you suggest? Thanks. I remember Catalani recommending 100% sphagnum, but he seems to say that for every species.
Chris