I've been growing my phals in temps around 64 in winter, and have been told that those temps are much too cold. I have to say that it's not so in my case as the past 2 years I've had the best growth and flowering ever. I've been growing 7 years now, and have had more success with mine (30) providing bottom heat and staying in low to mid 60's thru winter. I grow indoors only, 17 under ligjts, the rest in an East window.