After harvest, when the crop needs to be propagated, the gardener leaves some seeds for sowing. No matter how good the weather is, immediate sowing will not form seedlings. This is because the germ of a seed necessarily goes through a dormant period. The length of the dormancy period is determined by the seeds’ physiology, the plant’s growing season (which begins in spring and ends in autumn). If all types of crop seeds were germinated immediately in the fall, the plant would die due to weather conditions incompatible with the life of the young germ.
There are special chemicals in seeds that block developmental mechanisms. These substances are called growth blockers or inhibitors. Gradually, their number in the seeds decreases and the inhibitors are replaced by other chemicals called growth promoters, which are used to influence the physiological processes in the seeds. They awaken the embryo from dormancy (hibernation) and include developmental mechanisms that ensure germination, growth, and plant development. This is when stratification seeds are needed, and how to do this at home is described in this article.
WHY IS THE STRATIFICATION SEEDS PROCESS NECESSARY?
The process of transition from a dormant to an active state under the influence of external influences on the seed is called stratification seeds. In fact, stratification seeds prepare the embryo for development. Seeds undergoing stratification seeds treatment require certain conditions: favorable ambient temperature and humidity. These lead to softening, cracking, and hardening of the seed’s hard shell. Under the influence of moisture, the seed swells and begins the physiological process of converting complex, high molecular weight organic substances into simpler substances available for embryonic nutrition.
Without stratification, seeds do not germinate, especially in the case of sudden changes in temperature and humidity conditions in the central and northern regions. In areas with little change in climatic conditions, seeds do not need a dormant period and reproduce year-round.
Most plants have stratification seeds for between 1 and 6 months, but some perennial crops have stratification seeds for up to 2 years (Table 1). Stratification seeds are also required for most flowering crops, especially when sown in spring, some of which are listed in Table 2.
The main purpose of stratification seeds is to shorten the dormancy period under artificially created conditions and awaken the growth and development of embryos, i.e., to emerge seedlings quickly before the target date.
Table 1: Timing of low-temperature stratification of perennial crops
|Culture||Duration of stratification, days|
|Cherry plum||120-180, 130-150|
|Common cherry, chokeberry||150-180|
|Magonia, grapes, prince||120-140|
|Plum, blackthorn, rowan||120-180, 150-180|
|Bird cherry, lilac, aconite, catchment, hosta, anemone||30-50|
TYPES OF STRATIFICATION SEEDS
In practice, there are several types of stratification seeds that are used.
The need, duration and type of stratification seeds are usually indicated on the seed package or the manual. Dried seeds that have had organic residues removed should be placed in the stratification seeds process. Otherwise, they will rot in a humid environment (apples, pears).
Cold stratification seeds
The cold stratification seeds method is usually applied to perennial seed crops with a clear distinction between cold and warm periods, ending the growing season in autumn. This type of stratification seeds is required for crops in temperate regions. Seeds are placed at air temperature of 32-39 °F (0-4ºС) and humidity of 65-75%.
The duration of stratification in these cases can be 1-6 months. It is used for seeds, drupes, some vegetables, flowers and other crops. If plants do not pass the cooling stage, they may not germinate in the spring. In other words, stratification mimics the winter sowing of some crops, when conditions are provided for embryos to rest and subsequently awaken to growth and development.
Some seeds that require a temporary stay at low temperatures may also germinate without stratification. However, in this case the seedlings will be sparse and unfriendly (buckthorn, honeysuckle, strawberry).
Warm stratification differs from Cold stratification in that it is short-lived. Vegetable crops are usually subjected to Hot, Warm stratification. Dry seeds can be kept in an anaerobic state for a long time. But raising the temperature to 64-71 °F (18-22 ºC) and the humidity to no less than 70% will awaken the life process. For example, soaking tomatoes, peppers, cucumbers, and eggplants in warm water and leaving them in a warm place will cause the seeds to emerge from the disease after a day or two.
Combining stratification seeds
The combined stratification method is applied to tightly matured seeds and crops from some regions where it is necessary to simulate the seasons to improve germination rates. These are usually seeds of perennial plants with thick skin and dense flesh (hawthorn, lingonberry, snowberry, yew, apricot, plum).
Hawthorn and rhododendron seeds require a long (7-8 months) stratification period. To soften the hard shell and awaken the germ, the seeds are first cultivated in containers at 68-77 °F (20-25ºС) for 4 months, then in the cellar or the shade at 32-41 °F (0-5ºС) stratification seeds for 5-6 months. For yew and some maple species, a warm stratification period of 1-1.5 months is sufficient, and then the seeds are placed on Cold stratification seeds.
Stage stratification seeds
This is the most complex type of multi-stage stratification of seeds. It consists of several cycles with low and high temperatures. For example, the seeds of some peony species and cation are stored several times at alternating high and low temperatures.
Primroses, watercress and ocotilloes were repeatedly frozen. Before sowing, their seeds were placed in water at room temperature of 64 °F (18ºC) during the day and kept in the refrigerator overnight for 5-7 days. In this case, the seeds germinated at a high and friendly rate.
METHODS OF STRATIFICATION SEEDS AT HOME
Dry stratification seeds
- The seeds to be stratified should be previously purified. Soak in a 0.5% manganese solution for 0.5 hours. Then rinse with a small amount of water at room temperature. After they are dry, they are placed in polyethylene bags, marked in detail with the species, variety, and date of stratification. Place the bags in the upper level of the refrigerator or in a room with a temperature of 32-37-39 °F (0-3-4ºC) before sowing.
- Place the sterilized dry seeds in flax or polyethylene bags in a plastic container with a tightly closed lid and secure with tape. Bury the bag in the snow until it melts. As it warms up, move it to the bottom of the cellar or refrigerator until sowing.
The phenomenon of stratification seeds in cabbage sprouts
Ideal for Cold stratification seeds at home.
Separate late-ripening cabbage from the head. Cut the roots. Chop the core of the core. Fill the container with seeds. Tightly seal and tape the lid from the remains of the core. The “goblet” with the seeds (like our ancestors did with gold coins) we bury vertically in a hole in the ground as deep as a shovel bayonet.
We covered it with dirt. We set a numbered marker, and in the diary, we write down under its number information about the seed, indicating the type and variety of the crop, the time of planting, and the end of stratification. In spring, when the topsoil warms up to the desired temperature of the crop, the seed stems are dug up and sown on the prepared beds.
Wet stratification seeds
- Grinding. Prepare the substrate in a container, which can be coarse river-washed sand, decayed sawdust, peat, moss. It is very important that the seeds are thoroughly cleaned of organic residues, sterilized, and dried. The container should be filled with 2/3 of the moist substrate. Spread out the prepared seeds and cover them with the substrate. While moistening the substrate, it is treated with a bio fungicide to prevent fungal infection: trichothecene, phytosporin, and others. The treatment is usually indicated on the package. Cover the container with a lid and place it in a plastic bag to keep it moist. Place the packaged container on the bottom shelf of the refrigerator. The temperature should be between 37-39 °F (3-4ºС). At the end of the stratification seeds period, the bags should be transferred to a lower temperature of 33 °F (1ºC). In addition, the containers are regularly checked to monitor the condition of the seeds and, if necessary, to moisten the substrate.
- Stratification in cloth rolls. Spread a thin layer of moss or cotton wool on a natural cloth strip 4-5 inches (10-13 cm) wide and 12-14 inches (30-35 cm) long. Carefully place the seeds. Bend the long side of the cloth strip, which will cover the seeds on top, and roll it into a roll. Tie it up and soak it in water to absorb the water. Carefully squeeze out any excess water. Wrap the roll in a cellophane bag and place it on the bottom shelf of the refrigerator. Label or number each roll and describe it in detail in your garden journal. Systematically check the humidity of the rolls during stratification seeds. Check the condition of the seeds. If a fungal infestation is found, clean, disinfect, dry, and repeat the entire stratification seeds process on new material.
Some crops are sown and planted in the soil in autumn (overwintering), and stratification seeds are performed under natural conditions (winter garlic, herbs, certain salad varieties).
There are other ways to perform stratification seeds besides the above-mentioned methods. Remember! Stratification seeds will save you from suffering from low or no seedlings in spring.
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