
Why Didn’t These Seeds Germinate?
A seed is a living organism, a small embryonic plant in a state of dormancy, marking the beginning of a new generation’s life. It is the means by which plants reproduce and spread, ensuring the continuity of their species. In botany, a seed is a fertilized ovule formed from the ovary of a flower. It consists of an embryo surrounded by a protective coat called the seed coat and a supply of stored food, either within parts of the embryo (non-endospermic seed) or separately in a tissue called the endosperm (endospermic seed).
The embryo itself contains the same basic organs as an adult plant, namely the root, stem, and leaves, but in a miniature form. These are called the radicle, hypocotyl, and cotyledons, which can be either monocotyledonous (monocots) like wheat, barley, and palms, or dicotyledonous (dicots) like beans, lentils, and most trees.
How Does Seed Germination Occur?
Germination begins when water penetrates the seed coats, causing the embryo to swell and break through the seed coat. The radicle extends downward into the soil, while the hypocotyl grows upward, carrying the cotyledons and the plumule above the soil surface. The cotyledons eventually shrivel and fall off after providing the necessary nutrients for germination, while the plumule turns green, grows, and differentiates into the stem and leaves. The radicle branches out underground, forming the plant’s root system.
Why Do Seeds Sometimes Fail to Germinate?
A variety of internal and external factors influence seed germination. Here, we focus on the external factors that affect germination:
- Water
Water plays a crucial role in the germination process. A seed absorbs water ranging from 40% to 150% of its dry weight, causing it to swell, break its membranes, and allow the radicle to emerge, initiating germination. Water also reactivates the embryo’s cellular activity by hydrating stored nutrients and increasing gas exchange after membrane rupture.
Different plant species require varying amounts of water for germination. Oilseeds, like castor beans, need less water compared to starchy seeds, like corn. It is important to note that only free water can penetrate the seed, and for germination to occur, soil moisture content should not fall below the permanent wilting point. Additionally, excessive water should be avoided, as it can lead to seed rot due to poor aeration.

- Oxygen (O2)
Most plants need oxygen during germination, which occurs efficiently under good aeration and appropriate oxygen levels. Germination is hampered in compacted soils and swampy clays that lack sufficient oxygen. The resumption of respiratory activity, which is minimal during dormancy, increases significantly at the start of germination, reaching a peak before stabilizing at normal levels. Some seeds can begin germination without oxygen, such as Vicia sativa and clover seeds. However, exceptions include plants like rice, Cynodon dactylon, and Typha that thrive in low-oxygen, waterlogged environments.
- Temperature
Optimal germination temperature varies among crops. The attached table shows the optimal temperatures for germinating various crops, which represent the fewest days required for germination at a specific temperature.
- Light
About 70% of plants germinate in the presence of light, making it preferable to sow their seeds at the soil surface. Conversely, 25% of plants require darkness for germination, and the remaining percentage can germinate in both light and darkness without issue, such as grains and legumes. Visible sunlight comprises several colors with different wavelengths: violet, blue, green, yellow, orange, and red. Green wavelengths are reflected by plant leaves, making them appear green, while blue light scatters, giving the sky its blue hue. Red light significantly influences seed germination by promoting the absorption of phytochrome, which is essential for the process.
In addition to these factors, the presence of certain organisms in the germination plays varying roles:
- Some inhibit germination, like roots secreting substances that prevent the germination of nearby species or the substances within tomato fruits that inhibit seed germination.
- Others promote germination, such as root exudates from host plants that activate parasitic plants like Orobanche.
- Symbiotic relationships, as seen in some orchids, where mycorrhizal fungi induce germination and provide essential nutrients, including rare elements, necessary for plant growth.
Understanding these factors helps us identify why certain seeds fail to germinate under specific conditions and allows us to store seeds properly to ensure they are ready to germinate when the right conditions are met.
by Eng. Nour El Dein Haydarieh