The Effect of Water Temperature on Bean Seeds

Temperature Effects on Germination

• Four major environmental factors influence germination: temperature, water, gases and light. Temperature is the most important factor and regulates the timing of germination. Temperature plays a role in dormancy control and is effective at different degrees, depending upon the plant. Every plant has three temperature points: minimum, optimum and maximum, and beans are no exception. The minimum temperature beans can germinate at is 60 degrees Fahrenheit, with the maximum temperature at 95 degrees Fahrenheit. The best germination will come from the optimum temperature range, between 60 and 85 degrees Fahrenheit.

Water Effects on Germination

• The uptake of water into a dry seed is called imbibition. Factors influencing the rate of water uptake into the seed include the following: pore structure (texture) of the germination medium; media compaction; and the closeness and distribution of soil-seed contact. The relationship between the soil and the seed is the number one reason why a bean seed may or may not germinate. If the bean seed were to soak up all the water immediately available around the seed, and the soil had large gaps or air pockets, the seed would not obtain any further water for imbibition.

Why Water Temperature Is Important

• Water and temperature play different roles in the process of germination, but the combination can also be studied. A simple science experiment taking beans and germinating them with different temperatures of water will have different results. Beans will have a better germination percentage given room temperature water and less with chilled or heated water. Understanding the different roles that water and temperature play in germination, this can be explained. The water temperature will change the temperature of the soil, affecting the dormancy of the seed, which will allow for germination to begin or for the seed to remain in a dormant state.

Digging Deeper

• How temperature affects dormancy is an interesting science. It not only involves a physical change in the seed, but also involves a major change in the seeds metabolism. When a seed is developing, it is synthesizing reserve foods around the embryo. In germination, it is the breakdown of these food reserves that is vital in sustaining the cotyledon (first leaves) until it reaches the surface and starts to photosynthesize. Temperature is thought to activate enzymes to start the metabolic machinery for initiating germination. Another interesting fact comes from a study done by Bruce M. Pollock that shows the relationship between initial seed moisture and temperature effects. If a bean seed is imbibed 20 percent before planting, the effects of soil temperature will not have as great an impact on germination percentage.