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Seeds are not always directly germinable, but require certain stimuli in order to germinate. For example, so-called cold or frost germs need a cold stimulus before they start to germinate. This cold stimulus can be simulated, namely with stratification. We will explain to you what is behind the term "stratification" and how you can use this method.
Stratify
Stratification is a process that breaks the germination inhibition of certain plants. The term "stratification" comes from the Latin word "stratum" which means "cover" or "layer". This designation is based on the original procedure of stratification, because unlike today, the seed was simply embedded in layers in the substrate. Nowadays, however, a different procedure has been established for interrupting the germination inhibition. Stratification is mainly used in young plant operations and frost nurseries, but hobby gardeners also benefit from this process:
- Seeds emerge evenly
- thus higher harvest yield possible
- fewer low-quality plants
What is germination inhibition?
The germination inhibition is a kind of internal clock of the seeds, which protects them from germinating too early. A good example of this are different trees and shrubs whose seeds ripen in late summer or autumn. If these were to germinate directly, they would have little chance of survival, as they would have to survive the winter and frost. To ensure the seeds have the best possible chance of surviving, sprout inhibition kicks in and prevents them from germinating before winter. But not only trees and shrubs are typical cold germs, because a large number of different plants belong to this group:
- wild garlic
- Sweet Violet
- cloudberry
- plum
- bluebell
- Poppy
Difference between cold and frost germs
Cold germs used to be subdivided into different groups, namely cool and frost germs. The reason for this was that some plants require significantly lower temperatures for germination than others. Nowadays, however, the distinction between cool, cold and frost germs is no longer common, so that all plants are assigned to the cold germs group. However, it is quite possible that cold germs are still referred to as frost germs today.
Stratify cold germs
The stratification of cold germs is used very often and at the same time has high chances of success. The hobby gardener can also try stratification, because this process is relatively simple. The required equipment is also manageable, because only a box, a fine-mesh grid and substrate are required. A sharp-edged screed sand or a sand-peat mixture is suitable as a substrate. You should refrain from normal garden soil or even compost, as there are usually many harmful seedlings in them and thus promote mold. To stratify the cold germs, it is best to proceed as follows:
- Protect crate with fine-mesh grid
- provides protection from mice and birds
- Fill substrate in box
- Put seeds in
- Put the box outside
- preferably sheltered and shady location
- Crate must be exposed to the weather!
- about 2°C - 8°C
- freezing temperatures are not required
- keep evenly moist
The crate must now remain in place for a few weeks and you should check it at least once a week. When checking, it is also advisable to turn the entire mixture several times. Because this measure roughens the shell of the seeds, making them germinable faster. This is particularly worthwhile for hard-shelled seeds, as these usually take a little longer to germinate.
Note: Instead of placing the seeds in a box directly outside, other stratification methods have proven their worth. You can also store the seeds in a plastic bag filled with sand in the fridge or in the basement.
Warm-cold stratification
Another method of making seeds germinable is warm-cold stratification. Basically, it works almost exactly like cold stratification, but with the difference that these are initially exposed to higher temperatures for about two to four weeks. Only after this warm period are the seeds exposed to the cold stimulus. The preceding heat accelerates the swelling of hard seed coats, so that the seeds can germinate more quickly. Plants with hard seed coats are among others
- witch hazel (witch hazel)
- Yew (taxus)
- some snowball species (Viburnum)
When are seeds sown?
The optimal time to sow the seeds is generally as soon as the first of them germinate. It is therefore advisable to check them on a weekly basis. As soon as you can see that the seeds are germinating, you can sow them all - provided the time is suitable for sowing. For example, if the seeds are already germinating in January, you should wait a little longer before sowing and continue to store the seeds at -2 °C to -4 °C.
notice: When sowing, the substrate can be sieved off beforehand if necessary, but it is also possible that the sand is simply sown with it.