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Seeds are the harbingers of plant life. The life cycle of plants starts and ends with them. This statement definitely intrigues you as it implies that seeds live and die; but are they living or nonliving things?
Seeds are living things! However, they are living in a dormant (resting) state which means that they require very little resources to stay alive until the ideal conditions for their growth occur.
Apart from the ideal conditions for their growth being met, the other major determinant of the life of a seed is its particular life span. In the rest of this article, we will present you with valuable and interesting information about seeds.
What are seeds really?
A seed can simply be described as the most important part of a plant. It is the embryo of a plant-covered by a seed coat. It usually contains some stored food and is produced when the ovules fertilize. It is usually found inside the fruit of a plant and produces a new plant when sowed in the ground.
Does a seed die?
Yes, like other living things, seeds die! The situation is a bit tricky as they can also remain in a state of dormancy for long which means that though there are not technically dead, they won’t grow or germinate. However, they can be said to be dead when they are exposed to extreme conditions such as high temperatures from excessive sunlight or other sources of heat, and humidity that destroy their cell structures.
The life or death of seeds depends on certain factors. These factors include:
- Storage: This describes the way they are stored. The ideal storage condition is to keep them in a cool, dry place at a temperature of about 50ºF and at 50% humidity. Their viability will be affected exponentially by the degree of divergence from these ideal conditions. They can be placed in sealed, moisture-proof, glass containers and stored away in a refrigerator. They can also be placed in airtight and watertight containers such as food jars, or in zip lock bags placed inside a jar.
Depending on their condition and how they are stored, different seeds have different average shelf lives. Onions, parsley, spinach, and parsnips will remain viable for one year; dandelion, okra, beans, corn, and peas – two years; carrots, asparagus, rutabagas, and leeks – 3 years; peppers, pumpkins, chard, watermelons, artichokes, and basil – four years; while beets, tomatoes, cucumbers, lettuce, muskmelons, chicory, celery, endive, and eggplant if properly stored, can remain viable for up to five years.
- Age: Most seeds will remain viable or alive for up to one year while many others will remain viable for up to two years. The more the number of years they are stored, the less viable they become as their germination rate drops off exponentially. This doesn’t mean that they will not germinate and grow into healthy plants; it only means that you need to sow more of them as not all will germinate.
- Condition: Some seeds will never germinate no matter how well they are stored or their age. This condition of dormancy results when the external conditions are ideal but the state of the seed makes it not germinate. Seed dormancy can be classified into four major types. It can be endogenous, exogenous, secondary, or combinational.
Endogenous dormancy is related to conditions within the embryo of the seed itself. It can be in the form of:
Physical dormancy is a situation where the seed coat is hard and thus prevents the penetration of moisture which is necessary for the fertilization of the ovules. The seed cannot germinate and can be said to be ‘dead’. Plants that are typically prone to physical dormancy include Malvaceae, Cannaceae, and Anacardiaceae.
Chemical dormancy occurs when rainwater or melting snow leaches a certain chemical constituent out of the seed and prevents germination. The absence of such chemicals will prevent conditions suitable for the fertilization of the ovules and will keep the seed dormant.
Exogenous dormancy is related to conditions occurring outside the seed which are predominantly environmental conditions. These conditions include:
Photodormancy describes a situation where the sensitivity of light affects the germination of the seeds. Such seeds are said to be photoelastic and require given periods of light or darkness penetrating their embryos for germination to occur. If these light conditions are not met either because they are buried too deep in the ground or vice versa, they will remain dormant.
Thermodormancy describes a condition where the seed is sensitive to heat or cold. If the environmental temperature is not ideal they will remain dormant. Seeds of Amaranth or Cocklebur, for instance, only germinate at high temperatures between (30 °C or 86 °F); while Celery seeds, for instance, are better off with cool soil temperatures.
Secondary dormancy on the other hand is caused after the dispersal of the seed from the parent plant and it meets conditions that are not ideal for germination. Such conditions include falling on rocky ground or toxic soil or being exposed to an extreme temperature which may inhibit the sensitivity of the plasma membrane receptors and will prevent germination.
Conditional dormancy on its own part describes a situation where the embryo of the seed has physiological problems and its coat is also impermeable to water.
How long can a seed survive?
According to Ewart (1908), seeds can be divided into three categories according to the life span or expected longevity. They were classified as follows:
- Microbiotic: The average lifespan of seeds under this category is between a few weeks and three years.
- Mesobiotic: Their average life span is between three and fifteen years.
- Macrobiotic: These can last from fifteen to a hundred years or even more.
The seeds of most crop plants have short average life spans and belong to the microbiotic category. To keep them viable, extra care should be taken to ensure that they are stored in very ideal conditions. On the other hand, seeds of many wild plants and trees have strong seed coats and can be viable for up to fifty years or more.
Interestingly, studies have found that legume seeds have life spans up to seventy-five years and more. Seeds of the legumes C. Multijuga and Cassia Bicapsularis can remain viable for up to 100 years.
Seeds of the Indian Lotus (Nelumbo Nucifera) usually found in the soils of Manchuria have won credit for the highest life span as they can last for up to two hundred or four hundred years old.
Using Carbon dating techniques, the seed of the Judean Date Palm which is a cultivar of Phoenix Dactylifera has been declared to be up to two thousand years old! It was discovered under excavations at the palace of Herod the Great in Masada, Israel. It was sprouted in 2005 and is said to be the oldest seed to successfully grow into a plant.
How to Check the Viability of Seeds
The viability of seeds describes their ability to germinate into healthy seedlings despite growing in harsh or adverse conditions similar to those out there in the fields. It is a measure of their resistance to all forces challenging their germination.
We will show you a simple way of checking the viability of seeds through the germination test. The steps include:
- Collect a number of seeds from between fifty and a hundred.
- Place them on a moisturized paper towel or coffee filter.
- Wrap the paper around them while ensuring that the seeds are completely separated from each other.
- Place the folded paper inside a plastic bag and store it away in a warm place.
- Check them in two or three days’ time.
- Check them every day thereafter for the next week or so.
- Ensure that the paper is constantly moisturized.
- Check the seed packet to see the prescribed germination period. Check within that period to see the number of germinated seeds.
- Divide the number of seeds that germinated by the total number tested to determine the percentage of germination.
- Compare the germination percentage determined with that contained in the seed packet label.
- If your result is close or higher, then the seeds are viable and are good to plant. Consider purchasing a different set from a different store if the result is lower.
How to Induce Germination
Typically, horticulturists induce germination of seeds and you can do so too through any of the following ways:
- Scarification: This is a process of allowing water to penetrate the seed either by breaking the seed coat physically through soaking with water or softening with chemicals. It could also be by poking holes on them, scraping with sandpaper, or even cracking with a hammer.
- Stratification: This is the process of adding moisture directly into the seeds to be absorbed. They are then moist-chilled in order to after-ripen the embryo. Stratifying can also be done by sowing the seeds in late summer or fall thus subjecting them to cool weather conditions.
- Leaching: Chemical inhibitors within some seeds that make germination difficult can also be leached out by soaking them in water or by exposing them to rain or melting snow. Twelve to Twenty-four hours of soaking is sufficient to induce germination in most garden seeds.