A brief lesson in photoperiodism...

Moonflowers are Short day plants

 Photoperiodism is the effect of the length of day and night on plant growth and development.

The effect of photoperiod on flower development is diverse among plant species.  Not all plants respond the same. There are three distinct groups: Short day, Long day and Day neutral plants.

Short day = Long night

Long day = Short night

Long nights (Winter) and short nights (Summer) are really the basis for this effect in plants.  It is generally spoken of in terms of day length when in reality it is the amount of DARKNESS that triggers the flowering response. 

Moonflowers (see 10/1/2010 post) are one of the Short day plants we're very fond of...