As gardeners know all too well, as soon as the soil warms in spring, there will be a plethora of new weeds to contend with. These are the progeny of last year's flowers, and they have bided their time until conditions were just right for germination. By delaying germination until spring, they will maximize their growth before having to contend with their first winter.
Seeds use various chemical and mechanical means of inhibiting germination until the time is ripe.
But not all seeds go through a dormant period. Most seeds sold commercially through catalogs and nurseries have been hybridized for generations and will usually come up as soon as planted. Where the gardener is likely to encounter problems is with seeds of native and woody plants. But for seeds with thick, hard walls, even commercial seeds may need some help. In most cases, what is needed is a little faux winter.