I am sure that many gardeners have repeatedly encountered the problem of seeds that have been buried in the ground for a long time but for no apparent reason do not germinate. In this Bubgo article, I will discuss the reasons why this happens and an effective agricultural method - seed stratification, which promotes seed germination.
And failure is a natural cycle of plant development. In the natural environment, after seed maturation, plants enter a dormant period, when they are asleep and hibernate in the soil. At this time (from autumn to mid-spring), they are subject to various unfavorable weather conditions (mainly freezing). And in spring, when favorable conditions appear, the seeds germinate and the whole life cycle of the plant repeats itself over and over again.
Tips: Dormancy prevents premature germination and accidental seedling emergence. Certain substances, blockers, or growth inhibitors provide the biological mechanism for dormancy.
Over time, in the spring, the amount of these substances decreases due to cold temperatures, and they are replaced by new substances - growth stimulants. Buds will only appear in the following season. Sometimes seeds can remain dormant for several years. The long winter frost and moisture come into play: the seed coat becomes softer and breaks down. Nothing prevents the young embryo from bursting out now in search of light and nutrients.
A similar thing happens in everyday life. Seeds harvested in the fall are not prepared for a certain amount of cold and moisture. The number of inhibitors in them is enormous. They can also prevent germination. This is where the stratification method comes into play.
The term "stratification" appears in various fields: botany, medicine, chemistry, and even mathematics. Naturally, in each case, the concept is completely different. We are interested in biological concepts. What is stratification and why is this agricultural technique needed?
The word itself implies layers, stratification, or layering. It makes sense. A similar operation is performed in this method. Seeds for a long time were covered with various moist substances: moss, cotton, cloth, peat, etc. Since ancient times, sown seeds were placed between two layers of moist soil, so that they were stored without a cover over the winter.
Stratification is therefore an artificial creation of natural conditions: a frozen and moist state so that the physiological sleep of the seeds stops with time and they are ready for accelerated germination in spring.
In almost all cultures, seed material is in a state of physiological dormancy after maturation. In some plants, it is shallow and short, disappearing after normal dry storage. It is best to stratify seeds of most woody and shrubby plants as well as perennial herbs.
Which seeds do not need stratification?
1. crops grown in southern areas without low negative temperatures do not require stratification.
2. Plants that produce seeds in the first months of summer also do not need them because by autumn they are mature enough to be sown. Just a short soaking in water is sufficient.
3. Seeds of tomatoes, cucumbers, peppers, eggplants, and pumpkins do not need this preparation method. During winter and spring storage under normal home or warehouse conditions, they will go through a dormant phase.
In some cases, the dormancy of the seeds is delayed considerably, sometimes by up to two years. As a result, seeds are difficult to germinate. In some seeds, the embryo is surrounded by a hard shell and he is unable to break its integrity on his own. This is the time when it is necessary to force a reduction of the resting time because it is not always possible to wait for 7-12 months.
Tip: The purpose of stratification is to minimize the time for seeds to come out of dormancy and create conditions for their germination. There are several types of this technique.
1. Cold stratification
Store seeds at a low temperature of 32-41 °F (0-5°C) for one month and up to six months at up to 75% humidity. This method is suitable for most berry growers.
2. Warm stratification
Create conditions for seeds with sufficiently high stratification temperatures of 68-77 °F (20-25 °C). Duration - from about 35 °F (2°C) to 48 hours. Suitable for most annual vegetables: peppers, tomatoes, eggplants, watermelons, cucumbers. To awaken the seeds, immersion in water at a temperature of 64-71 °F (18-22°C) is sufficient. This time is sufficient to peck the seeds and plant them further.
3. Combinations
Corresponds to its name and provides an alternating combination of cold and warm stratification. It is used to accelerate the germination of hard-shelled seeds, more commonly drupes: apricots, hawthorn, plums, podocarpus. Seeds of these crops are first stored in a warm place at temperatures from 71-77 °F (22-25 degrees) for about 4 months, then in a refrigerator or cellar at temperatures of 32-41 °F (0-5°C) for about 6 months. For some crops, the heat aging stage can be shortened to 1-1.5 months (maple, redbud).
4. Stepping
Infrequently used due to its complexity and laboriousness. There are repetitive repetitions and combinations of the first two stratifications, accompanied by changes in temperature cooling and warming cycles. It is used to increase the germination of some flowering crops: fuchsias, clematis, cornflowers, and kiwis.
The exposure time of seeds to artificially created conditions varies. It ranges from one to two weeks to six months.
1. for perennial flower seeds, this method lasts from 2 to 4 months.
2. for delphinium, evening primrose, moonflower, 3-4 weeks is sufficient
3. for carrots, celery, parsley - no more than 2-3 weeks.
Tip: Podzimny sowing will allow natural stratification in winter.
Wet cold stratification methods.
1. The most common and easily available method is winter sowing
The process occurs under natural conditions. Many summer inhabitants do not even suspect that, for example, by planting garlic before winter, they thereby stratify this planting material.
2. Sanding
Performing this procedure is not difficult. Sterilized and dried seeds should be placed in prepared moistened coarse sand, packed in waterproof ziplock bags, and placed in a refrigerator on the bottom shelf, creating a temperature range of 37-39 °F (3-4°C). The temperature should be slightly reduced to 34 °F (1 °C) near the time of sowing. Sand can be substituted with sawdust or peat and must be disinfected and moistened regularly to prevent drying. Usually, vermiculite is used instead of sand.
3. Use clean, long strips of white fabric
Use long strips of clean white fabric 15x4 inches (38x10 cm) seeds evenly distributed along the length and rolled up. All rolls of fabric prepared in this way are folded into a suitable container and a small amount of water is added to it. You need enough water so that the rolls are slightly moistened, but not completely immersed in water, as air entry is important for the seeds. Do not forget to bind to each roll a label with the name and date of the beginning of the stratification. It should be kept in a room with low positive temperature values.
4. Using peat moss
Place the rolls prepared by the above method in a container and cover them with well-moistened moss. Don't forget to moisten the moss in time. You can layout and just seeds.
Tip: The substrate for storing seeds needs a 3:1 ratio. It should be moderately moist. Otherwise, they will either germinate prematurely or mold will appear.
Cold stratified drying method.
1. the seeds are sterilized in a 0.5% potassium permanganate solution, another preparation, herbal or trace element infusion for about half an hour.
2. In addition, after repeated washing with water, the seeds are dried and poured into plastic bags with zippers (fasteners).
3. after completing all procedures, place the package on the bottom shelf of the refrigerator at a temperature of 32-41 °F (0-5 °C) until sowing time.
There is a slightly different method: Seeds prepared as described above are placed in resealable plastic containers and buried in snow at low temperatures for a period of time. When warm days arrive, these seeds are transferred to the refrigerator until sowing time.
A very unusual method of layering in stumps of late-maturing cabbage. A core is cut out of the stem and the seeds of the desired crop are placed. The cut-out is then wrapped in tape around the stump, thus closing the cavity with seeds. In addition, bury the poker vertically into the ground up to the depth of the spatula bayonet.
Do not forget to attach any labels to avoid losing the spring. Once the snow has melted and the soil has thawed, the stems with the seed material will be removed from the ground. You are ready to start planting.
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