Thanks for the info Hongrui!
I suppose humidity, time and again, is indeed the culprit to my failure in growing amps. Therefore I think the only solution is getting them to grow in enclosed environment, like in a tank. The only thing I don't understand is where some humidity-loving plants can still grow well in my garden. Plants like moss and ferns grow like weeds and phalaeopsis orchids seem to do well too.
Oh well, exceptional circumstances can limit the plants you can grow
