From March to May (spring) and September to November (autumn), Sikkim has pleasant weather with occasional rains. The temperatures don't fluctuate too much.(day: + 14 to + 25 / night +8 to + 18 C). Spring is peak-season for flowers and autumn for mountain-views. In spring you may also enjoy moutain-views in the early mornings.
From late June to August/mid-September, monsoon brings lots of rainfall and humidity with pleasant temperatures (day: 20 - 30 C / night: 17 - 25 C).
Winter is from December to February and comes with colder temperatures (day: +10 - + 18 / night + 5 - + 15) and from January to February with occasional rains. The snowline in winter lies at above 2000 m, in summer at above 4000 m. Bamboo Retreat lies at 1500 m.a.s.l. and well below the snow-line.
The best time to visit Sikkim for flowers and birds with pleasant temperatures is from March to June.
The best time to visit Sikkim for best moutain-views with pleasant temperatures is from October to November.
If you do not mind dressing up warmly, especially at night, the best time to visit Sikkim for mask-dances, calm and less tourists is from December to February.
The best time to visit Sikkim for less tourists, lush greenery and monsoon-feeling with pleasant temperatures is from July to August.