Here we give you a little information for a better understanding why seeds are dormant, what scarification and stratification mean, what warm germs and cold germs are.
Why are the seeds dormant and what does that mean? Most seeds are dormant so that they do not germinate prematurely under unfavorable conditions, or they have a sprout inhibitor. Dormancy is caused by the hard seed coat, the pericarp, immature embryos, the seed coat drying out during ripening, or inhibitors in the seed. In the case of seed ripening with still immature embryos such as Ilex species, these only sprout when the germ has developed further. This usually takes about 2 months at about 20°C. When the seedling has matured, germination can take place. In species with fleshy fruits, such as magnolias, this is only lifted when the pulp has been removed before they ripen. We also speak of dormancy when ideal conditions such as temperature, humidity and light, depending on the type, are given and these do not germinate. Most of the time, dormancy can only be broken by scarification and stratification, either naturally or artificially.
Many seed coats only become more permeable at lower or higher temperatures. Germination occurs when the seed is able to absorb moisture. In order to initiate germination, an appropriate pre-treatment is necessary to make the shell porous and permeable so that moisture can penetrate the surface. The most common method is to file, roughen with coarse emery paper, or carefully score with a knife, being careful not to file or cut too deeply. Then pour hot water over it and let it swell for about 12 - 48 hours, depending on the genus and species.
Stratification is the treatment of seeds to encourage germination. It has proven to be most effective if the seeds are exposed to temperature fluctuations before or after sowing, as is the case in nature. Light germinators and dust-fine seeds are an exception, but more on that later. We distinguish between cold, warm and light germs.
These species include cold-tolerant and frost-hardy plants and shrubs such as Asimina, magnolias, Acer, Carpinus, many perennials, but also climbing plants such as clematis. These seeds require a cold-wet treatment and should be treated outdoors with cold (autumn/winter) mixed with substrate in the refrigerator between 0 to 5°C or wrapped in moist layers of sand. The duration of this stratification ranges from 3-4 weeks or up to 20 weeks, depending on the depth of dormancy. Without this stratification, germination success is very low or total, in the worst case the seeds go back into a dormant state, which is then particularly difficult to break.
Most tropical and subtropical seeds do well with a germination temperature of 20-25ºC. If the required germination temperature is exceeded, germination can also be delayed and/or cause a second dormancy. Only warm house plants such as palm species, heliconias, cycads and also Nelumbo seeds require higher temperatures for germination.
Arbutus, Callistemon, Eucalyputus, Melaleuca, thyme, cacti, carnivorous plants and many others or the spores of tree ferns belong to the very fine seeds. These are not covered with substrate, very small seeds, such as Arbutus, only pressed down or only slightly covered with substrate and watered from below until the sowing container is soaked through to the surface. Such seeds/spores have little or no nutrients and cannot give the seedling the strength to penetrate the substrate to the surface. Germination therefore only occurs with the help of light. If they lack this, the ability to germinate is greatly reduced or fails to appear at all.
How is seeded and what do I need for this? Continue to the general sowing instructions
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