A perfectly healthy seed may not germinate for a long time; months, or possibly even years. There are multiple factors that determine the timing of germiantion. Through the beginning of the life cycle of a plant; the period between pollination to germination, there are several factors that essentially slow down, or delay the reproduction process of a plant. Most of these factors, that slow or delay the process, are actually helpful to the plant species.
How do these delaying factors actually help the seed? Seed germination requirements essentially help the seed grow under ideal conditions. The seed does not usually germinate until the conditions meet the requirements.
One of the biggest factors that delays seed germination is season. There are different plant species that can thrive in the different seasons throughout the year, however, one given plant species that thrives in spring may not be able to survive through winter. This factor slows the germination of a seed, and if the seed somehow germinates anyway, the chance of survival is low. The limitations of the seasons are ultimately beneficial to the plant species.
Another significant germination-delaying factor is food/water supply. If there is not enough nutrition in the environment, the plant will struggle, and may not survive, thus this is an important limiting factor. Germination should not happen if there is not a stable food supply. If there is lack of water in the environment, like nutrition, the plant has a low risk of survival. However, unlike nutrition, too much water can also be harmful to the plant species and can effect the timing of germination.
These are a small few of the many factors that delay or slow down the germination of a seed, there are many more factors that play an equally important role.