Temperature affects the percentage of seeds that germinate and the rate of germination. Seeds kept at higher temperatures are more likely to deteriorate and not germinate. Once seeds start to germinate, higher temperatures stimulate faster germination up to an optimal temperature, after which the speed of germination declines.
The optimal temperature for speed of germination varies by species. Dry seeds are more likely to germinate at higher temperatures, but wet seeds are less likely to germinate at higher temperatures. Alternating between cold and hot temperatures is likely to stimulate many wet seeds to germinate. Some species of seed are stimulated to germinate by very cold temperatures.