Other species such as maize, the smaller cereals and many legumes such as beans
and clovers will germinate in either light or darkness. The variety Grand Rapids lettuce
is inhibited by “far red” light (wavelength about 730 nm) but is stimulated by red light
(wavelength about 660 nm).
Breaking Seed Dormancy
To avoid the problem of dormancy seed may have to be processed in some way to break
dormancy, such as by using machines to scratch the testa or by leaving the seed moist
and at temperatures between 1°C and 10°C for several weeks.
As soon as the food producer or seed company understands the dormancy
mechanism of a certain species then it is relatively simple to mimic the appropriate
conditions of temperature, water and light so as to deceive the seed into breaking
dormancy.
- Germination and Temperature
Seed will only germinate between certain temperature ranges. For example, if lettuce
seed is planted in soil at 2°C or at 30°C it will not germinate, or only poorly. This is not
true dormancy but a characteristic of plants to improve their chance of survival by not
starting to grow in hostile conditions.
In hot conditions: to overcome this problem, which is at its most critical 3 or 4 hours
after sowing, plant the seeds in the cooler, evening temperature. Vice-versa in cold
places.
A dramatic example of the effect of temperature on germination is shown below.
Figure 8. The effect of temperature on germination of tomato seed- Styles of Germination
As shown in the drawings below, seed develops into seedlings in one of two ways: