Janos, this is not a problem just as long as there is neither salt in sand from the sea shore nor free lime, the ideal pH is between 4.5 to 6.O. Either riverine sand or glaciated sand derived from igneous rock, the courser the better, will be very satisfactory. Try a 50:50 mix with composted bark and gritty sand. There are over 800 + L. martagon and its congeners here such as LL. jankae, cattaniae, pilosiusculum, caucasicum, hansonii, etc, etc, plus virtually our whole collection chuntering along year after year flowering happily. The only caveat is to use a good liquid feed. Slugs and snails hate this regime. The bark must be truly composted but watch out for it locking up nitrogen so try e.g. 24:8:15 or something in the order by way of a slow release 15:10:10 or whatever is available in Hungary along similar lines, it needn't be too precise, its just what works best for us here now, lighten up on the N in late summer or early Autumn. During dry weather remember to stick to a steady water regime and just adapt. If you have a problem, as previously, get in touch. Iain