Since we are planning to cultivate several alpine flowers in our classroom we have to get through one important step when sowing seeds out of these areas, this is the so called stratification which in nature ensures that the plants start to grow in spring:
How to stratify seeds
The definition of stratification originally means a special treatment of seed to stimulate the germination. But in general stratification stands for a clammy mounting of seed. Often stratification is used as a synonym for the handling of cold germinators. Many of the foreign plant species in middle Europe (especially tree seeds) demand low temperatures to be able to germinate. In nature this behavior makes sense because it is granted that the seed will not germinate until the end of winter. During the cold spell many different biochemical processes are executed inside the seed. Thereby substances are generated which are stimulating the germination process. This cold spell normally is called stratification.
In general there are the following steps during the sowing:
First the seed should be sowed in autumn or in the first days of the year. An ideal solution is the sowing in bowls. Also it is possible to sow directly in the garden. But this only makes sense if a huge amount of seed is available because birds or other animals are seeing it as food. As an alternative the cold treatment could be done inside of a refrigerator. This method is more successful for fewer seed than the sowing outside. For the refrigerator it is advisable not to sow the seed in bowls. It is more effective to use clammy sand, perlite or to stack tissues in a plastic bag. This method lowers the danger of mould.
If the cold treatment should take place in a refrigerator the following steps are necessary:
The seed has to be warmed up for two till four weeks at a place with 20 degrees. The substrate has to stay clammy but not wet. Then the seed has to be exposed to cold temperatures (-4 to 4 degree). The refrigerator has to be adjusted to provide this environment. After a cold period of four to six weeks the seed can be removed and can be sowed into a jar filled with soil. It is important to keep the seed away from higher temperatures. The best temperatures are five to twelve degree even if a germination can be seen.