The ability of weeds to spread their germination over a long period of time is vital to avoid unfavourable conditions. This is the phenomenon of seed dormancy.

Weeds may be contrasted with most crops which have been selected both consciously and unconsciously by scientists for rapid, uniform and immediate germination without any dormant period. Such behaviour in an annual weed would mean that it could be eliminated entirely by one or two years of careful cultivation.

Dormancy in seeds is often considered to fall into three categories.

Innate dormancy (dormant when shed from plant)

Induced dormancy

In this form of dormancy seeds that would normally germinate are prevented by an unfavourable environmental parameter. However, when the seeds are returned to a favourable environment they are unable to germinate.

Enforced dormancy

In this form of dormancy seeds are prevented from germinating by the lack of a key environmental factor such as moisture, oxygen, or low temperature. However, the seeds are able to germinate when the missing factor is supplied. Many weed species show a marked periodicity of germination because of enforced dormancy during part of the year.

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Steve Adkins