Nerine sarniensis create their flower spikes 2 years in advance, after each flowering a new spike will develop in the centre of the bulb.  We believe that the trigger for flowering is temperature based. We have noticed that the timing of flowering, sometimes earlier, sometimes later, is triggered by day/night temperature fluctuation in August or early September of at least 15 degrees Centigrade between day and night. Pull out the dead spike, do not cut it.