Stratification is a method that promotes better germination of seed material. The term itself means interbedding, which takes place, since the seeds are really covered with a damp substance like peat, moss or cotton wool, and left for a certain time.
Cold stratification has been practiced by gardeners for a long time and is often expressed in storing seeds in basements, trenches, in which low, although plus, temperatures reign. The winter sowing method is also a variation of this procedure when it is carried out in vivo
Types of stratification
In horticultural practice, several types of stratification are used - cold and warm, and for particularly hard-like seeds, the combined stratification method is used, in which the seeds are subjected to alternately warm and cold temperatures. The type of procedure is selected depending on the type of culture. Useful information about this can often be found on a bag of seed. For the most part, cold stratification is needed when the seeds are placed in conditions with temperatures from 0 ° to + 4 ° for a rather long period (2-4 months). The procedure must be started in advance, so that by the time of sowing, the seeds were prepared in the right way.
In many plant species, the embryos in the seeds are immersed in a state of deep dormancy, so that they are not able to germinate immediately after sowing. The rest period is determined by the season, climatic and meteorological conditions. A large number of plant species growing in the temperate zone are immersed in dormancy all autumn and winter, since if they germinated immediately after shedding and getting into the soil, small sprouts would inevitably die in cold winter weather. Therefore, special substances called blockers, growth inhibitors include a biological mechanism of rest. During the winter, the number of inhibitors gradually decreases, and the number of growth stimulants increases. Such a mechanism functions in nature, ensuring seed germination in spring.
Other happens on a summer garden plot on which in the spring inexperienced gardeners sow seeds which have not passed preparation. In these seeds, inhibitors are present in high concentration and inhibit germination. Naturally, as long as the biological mechanism of dormancy is in effect, the seeds will not sprout, although there is a small chance that they will germinate next year if they do not die. But gardeners more often blame their failures for poor seed quality and blame sellers.
Stratification actually mimics the natural conditions, so that under the influence of the cold the dormant state ceases and the embryos are ready for development.
The seeds of which plants need stratification
The procedure is not needed for cultures whose usual habitat is the tropics, the southern regions that do not know the cold winter. Seeds are also dispensed with without it, the ripening period of which occurs in the first half of the summer and by the time they are already germinating. As a rule, it is enough to soak such seeds in water for a day before sowing. In general, in many southern cultures (tomato, pepper, eggplant, pumpkin), the dormant period is so short that it manages to end in the time that the seed material is stored until the seed is sown. So stratification is useless for such plants.
But there are plants, usually their homeland are subtropics with a mild winter, which require warm or combined stratification. The seeds of these plant species are characterized by a pronounced dormant period, and stratification to awaken them to life is necessary. We can say that stratification for them creates the illusion of changing seasons (holly, yew).
The largest group consists of plants to which the cold stratification method is applied. Such plants usually live in regions with pronounced winter, even if not very harsh. Most often these are species growing in the temperate climatic zone.
It is worth noting that there are plants that will germinate even without cold stratification, but the percentage of germination will be noticeably worse. Among such crops can be called strawberries, sea buckthorn, honeysuckle.
Cold stratification procedure
The procedures may vary slightly, but common to them is placing the seeds in conditions of high humidity at a low plus temperature.
A time-tested method - placing seeds in moistened coarse-grained clean sand or peat. The ratio of seeds to sand (peat) is 1 to 3. After mixing the seeds with sand, they are watered from the watering can until the water comes out, then they are kept for several days (depending on the particular stratified culture). For example, it is recommended to withstand walnuts for 3 days, and apple and pear for 6 days. Freshly picked seeds are already wet, so moisturize them less.
After a few days, when the seeds swell, they must be scattered with the sand and dried to a state of light moisture. After that, the seeds and sand are poured into boxes and placed in a cold room (cellar, basement) with a temperature of + 2 ° ... + 5 °. Seed boxes must be provided with openings on the bottom and side walls so that air circulates and excess water can drain.
While the seeds go through the stratification process, they should be inspected every 10-15 days to remove spoiled seeds and maintain the desired degree of moisture. This stage of stratification will end with the emergence of root buds. Then the boxes together with the seeds inside should be thoroughly cooled, for which, for example, dig deeper into the snow and keep it until spring and the beginning of sowing.
The described method is advisable to use in the presence of large batches of seeds, but if there are not so many seeds for stratification, then other methods can be used.
- Sow the seeds in a bowl of wet peat. Wrap the plates with plastic wrap with ventilation holes and put them in the bottom of the refrigerator.
- A small amount of peat soil is poured into the pot, a layer of seeds is poured, again a layer of soil, another layer of seeds, which is covered with a soil layer. Lightly watered and, putting the pot in a film of polyethylene, sent to the refrigerator, on one of the lower shelves.
- For another useful method of stratification, you need pure white material, which must be torn into several long flaps, the approximate parameters are 10x40 cm. Spread the seeds on these flaps, trying to distribute them evenly, then bend the long ends of the flap, and twist the side parts in the manner of a roll. As a result, the seed will evenly lie along the entire length of the flap without the risk of waking up. A label should be attached to each roll on the wire indicating the type of seeds and the date the stratification began.
All rolls with seeds are stacked in a suitable container. A little water is poured into the container so that all the rolls get wet, but do not immerse in water. There is no way to prevent the sinking of the rolls, otherwise the water will displace the air and the germinating seeds will not have enough air, since the air requirements at this stage are quite high.
A more advanced method involves wetting seed rolls with sphagnum moss. This moss can hold a volume ten times its mass. In this case, the rolls laid out in a container are covered with well-moistened moss.
A container with rolls should be taken to a place with a low positive temperature. Of course, you need to make sure that the rolls remain moist, and monitor the condition of the seeds.