What triggers the flowering of durians?

Based on observations of 110 durian plants, researchers have discovered that around 15 days of dry weather can trigger the flowering of durian plants. The flowering occurred around 50 days after an approximately 15-day dry spell, independent of whether the plant was grafted or grown from a seed. The study covered both seed-grown and grafted plants, and focussed on the timing at which individual plants flowered, measured against an extensive survey of weather conditions. The team found that durian plants flowered approximately 50 days after a prolonged period of dry weather. These dry spells needed to be long enough to show up in moving average traces, specifically periods where rainfall averaged over 15-day windows was less than 1 mm. Previous work had hinted at some correlation between either dryness or low temperature. This is the first time that the exact conditions had been pinned down with such accuracy, though they found no correlation with maximum or minimum temperature. They proposed that there was some relationship between the flowering of durian and the more general burst of flowering seen in the tropics following long dry spells. But such general flowering events require a longer dry spell of around 30 days to occur. This explains why durians tend to flower multiple times a year, while synchronised flowering across species occurs once every few years.