Usual cause is insufficient water at the roots. One of my favourites, Clarkia, haven't grown it for years, nor seen it either.

thanks bamboo, i will take more care when watering, one of my neighbors thought it could be acidic soil or some other sort of soil problem, my sister gave me them as part of a present for Christmas, there was about 5 sorts of seeds, a little book and a few other bits in this garden pack it was lovely and all the seeds have come and are doing well.