The seeds of many hardy garden plants germinate best when sown fresh, before the seed coat has had time to harden. Others need a period of cold to coax them into action. Many herbaceous perennials are carrying seeds now, so collect some for sowing. Scatter the seed sparsely in small trays or shallow pots of free-draining compost. Cover with a layer of fine grit to prevent the seeds being washed away and to stop moss and algae growing on the compost surface. Label with plant name, number of seeds and date of sowing. Stand the containers outside in a sheltered, north-facing area where they will not be subject to severe temperature fluctuations.