Internal conditions of the seed must be favorable for germination, that is, any physical, chemical, or physiological barriers to germination must have disappeared or must have been removed by the propagator. The first step in germination is absorption of water. An adequate, continuous supply of moisture is important to ensure germination. Once germination has begun, a dry period can kill the embryo. Some seeds will germinate over a wide range of temperatures, others have a narrow range.
Many species have minimum, maximum, and optimum temperatures at which they germinate.
When germination temperatures are listed, they are usually optimum temperatures. Respiration rate increases during germination. The medium in which the seeds are sown should be loose and well aerated. If the oxygen supply during germination is limited or reduced, germination can be severely retarded or inhibited. Other plants germinate best in the dark.