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Cultivation of Alpines:

For a start I should say that NZ alpines can be very tricky. They are very picky when it comes to the conditions they will tolerate. Even when they appear to be growing under optimal conditions they will suddenly keel over and die in a matter of days for no readily apparent reason. It must always be kept in mind that alpines have not evolved to grow near sea level. In the mountains, plants are growing over a much shorter period of the year than they can in our gardens. It may get very warm over the Summer in the mountains but at or near sea level, plants have to contend with all year round (comparatively) warm conditions. Without a cold winter, plants tend to grow all year round. The temperatures they experience at sea level even during winter are such that they think its summer all year round. Certain species cope with this better than others. For example Ranunculus spp. tend to shut down during winter no matter what.  Also an added stress at low altitudes is the generally dryer conditions. In the mountains almost every night there is some kind of fog and or heavy dew. Rain fall is also much higher than at sea level.
Alpines need very good drainage, fungi can attack if they are under or over watered. If they are left too dry and then watered phytophora can attack the roots or the vascular system of the plants, though it being damaged by drought stress. This means that the plant can rot from the top down and once it starts, its too late to do much. Another thing that will kill plants suddenly is removal of the  dead leaves from around there bases. The plant will go from having a few untidy looking dead leaves at the bottom to having 100% dead leaves in a week or two so sometimes neglect is much safer. This is especially true with Aciphylla and Celmisia. I'm not sure why this happens but it may allow pathogens to attack or the plant may dry out much faster. All I know it that I have lost some plants that have been around for several years because I have tidied them up!

So that's the bad news but how can we help NZ alpines, so they grow better for us? The best way is to re-pot plants in slightly bigger pots or renew the mix in troughs often. I have found that plants that are re-potted every 6 months into slightly bigger pots will keep growing and survive much better. I don't know if its the nutrients being used up or leached out or the amount of oxygen available to the roots or diseases and pest building up but regular renewal of the mix helps. It seems as long as the plant keeps growing it can withstand normal stress but once it stalls then things go down hill fast.
Alpines will grow better if they have a cool root run. You can plant them in a cool part of the garden, such as an area with morning sun only. Or you can plant between rocks or under a gravel bed. I use weed mat covered in gravel Some alpines will self seed into the gravel. It also keeps the leaves dry which is important.