Germination types and environmental factors - How seeds germinate

May 21, 2024

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Benji Freeman

Keimarten und Umgebungsfaktoren - Wie Samen keimen

Content of the article

The different ways - how seeds germinate
Various factors - environmental elements
Light
Oxygen
Temperature
Water
Stratification as a germination aid

Seeds are the foundation of our lives and crucial for the growth of all plant species. They contain everything a plant needs to develop into a healthy seedling. It's an impressive process, turning a small seed into a large, vibrant plant.

Various factors play an important role in seed germination, which can vary depending on the type of germination. These include, above all, light, oxygen, temperature, and water. Some seeds require light to germinate, while others are only activated for germination in the dark. Oxygen is needed for cellular respiration, which meets the energy needs of the growing embryo. Likewise, there are temperature ranges that promote or inhibit germination and thus influence the germination outcome. The supply of water is also crucial for successful germination, as it enables seed swelling and the activation of internal metabolic processes.

In addition, special characteristics, such as pretreatment or different germination times, significantly influence success. A good understanding of these factors helps prepare the seeds properly and ensure their successful growth.
In this article, we explain how and what conditions seeds need to germinate, as well as what factors need to be considered to overcome dormancy.

The different ways - how seeds germinate

After seeds germinate, seedlings develop according to two clearly defined processes.

Depending on the species, a distinction is made between an above-ground (epigeic) and a below-ground (hypigeic) germination type.

Epigeic germination (above ground)

In this type of germination, the peduncle, also called a hypocotyl, grows between the root and the cotyledons. This stalk forms a so-called hypocotyl hook—a curved outgrowth (hook shape) from the seed that helps it break through the soil or make contact with it. As soon as the seedling breaks through the soil or makes contact with the surface, the cotyledons, which were previously hidden within the seed, unfold.
The cotyledons are the first visible leaves of a seedling and are photosynthetically active, allowing them to convert light into energy to supply the plant with nutrients. After a few primary leaves have formed, the cotyledons later die, and the primary leaves take over all photosynthesis.

Examples of species with epigeal germination:
Tomato, potato, sunflower, eggplant, pepper, radish, pumpkin, cucumber

Epigaische_und_Hypogaische_Keimung_-_Epigeic_and_hypogeic_germination_-_www — Epigäische und hypogeische Keimung im Vergleich

Hypogeal germination (underground)

In subterranean germination, the epicotyl develops in the soil between the cotyledons and the first primary leaves. The epicotyl remains in the soil until the primary leaves break through the surface. Only then do the first leaves, capable of photosynthesis, become visible.
In this type of germination, the cotyledons often die while still in the soil, while the primary leaves take over photosynthesis directly.

Examples of species exhibiting hypogeal germination:
Pea, bean, broad bean, date palm, soybean

Various factors - environmental elements

Germination is a process, and certain conditions are necessary for successful germination.
Essential environmental elements must be considered to initiate a plant's important life cycle. To overcome seed dormancy and allow seeds to germinate successfully and develop into healthy plants, the following specific factors and environmental elements must be considered:

Light
Oxygen
Temperature
Water

Taking these factors into account when sowing and caring for seeds significantly determines the germination rate and increases the chance of successful germination and healthy plants.

Light

The factor of light plays an important role in the germination of plants, but the required intensity and duration of light exposure depend strongly on the respective plant species.

With regard to the light conditions during the germination process, we differentiate between light germinators and dark germinators.

Licht_-_Sonne_-_Light_-_Sun_-_www — Energie der Sonne - Das Lichtverhältnis ist entscheidend

For species known as light germinators, light is already a necessary aspect for germination. They grow on the soil's surface or are only lightly covered with soil, a maximum of 0.5 cm. Germination is controlled by factors such as light, temperature, water, and oxygen. In these species, light activates certain phytochromes that promote germination.

Species that require only darkness to germinate are called dark germinators. They are placed in the soil and completely covered with soil. The sowing depth is generally determined by the seed size. In these species, germination is primarily controlled by only three factors: water, temperature, and oxygen. Light can inhibit germination in dark germinators by activating certain hormones such as abscisic acid.

During germination, light is crucial for some plant species, but less important or even detrimental for others. After germination, light is generally important for the growth and development of young plants, as it enables photosynthesis. However, there are also species that react neutrally to light levels, such as microgreens and sprouting plants.
These plant species possess a balanced ratio of phytochromes, light-sensitive proteins that control germination. In light-independent germinators, germination is not strictly dependent on light or darkness, but rather is influenced by other factors such as temperature, humidity, and oxygen.

Oxygen

Seed germination is a highly complex biological process. For a dormant seed to develop into an active, growing plant, the seed needs not only water, temperature, and light, but also oxygen. Oxygen is a crucial factor in seed germination, often underestimated and ignored, but absolutely vital.

Why is oxygen important?

With the absorption of water by the seed, metabolism begins. The previously dormant embryo becomes active and requires energy to initiate cell division and growth. This energy is obtained through aerobic cellular respiration—a process that requires oxygen.

Aerobic respiration converts sugar stored in the seed, with the help of oxygen, into adenosine triphosphate—the cell's universal energy source.
In the process, the cells absorb water, which leads to rehydration and activation of biological processes—the starting signal for germination.

Without oxygen, the seed would have to resort to anaerobic processes, which provide significantly less energy and often lead to toxic byproducts.

Consequences of oxygen deficiency

A lack of oxygen can severely impair or even prevent germination. In heavily compacted soils or with excessive watering, which reduces the availability of air in the substrate, germination is slowed. As a result, the plant's energy needs cannot be met. This leads to impaired cell division, preventing roots from fully developing. Prolonged oxygen deprivation will result in the seedling dying.

Practical tips for optimal oxygen supply

A key prerequisite for healthy plant growth is the quality and structure of the soil. Loosening the soil plays a crucial role in this process, preventing compaction, which often occurs due to irrigation, root pressure, or mechanical stress. Loose soil allows for better air circulation, which provides the roots with sufficient oxygen, an essential factor for cellular respiration and nutrient uptake.

Equally important is avoiding waterlogging. If excess water can't drain away, it displaces the oxygen in the soil. This leads to oxygen deficiency, which inhibits root respiration and increases the risk of rot and root diseases. Good drainage is therefore essential, especially for potted plants or in heavy soils.

Choosing suitable substrates further supports these processes. Permeable materials such as vermiculite or perlite improve soil structure by retaining water while simultaneously draining excess moisture. They promote aeration and create a balanced moisture-air ratio in the root zone – ideal for vigorous plant growth.

Temperature

Temperature directly affects the growth rate, success rate, and even the health of the young plants.
When seeds come into contact with water, they need the right ambient temperature to activate their germination process. Enzymes begin their work, cell division begins, and the embryo develops. If it's too cold, these processes remain inactive; if it's too hot, they can be disrupted or even completely interrupted. Optimal temperatures prevent excessive moisture and the growth of harmful fungi.

The ideal temperature depends on the plant species. Nature is diverse; some seeds can only germinate after months of prolonged frost, after forest fires, or even volcanic eruptions.

To get an overview of the different temperature conditions during germination, we distinguish between five temperature ranges that are crucial for successful germination:

Frost germinators below -5°C
Cold germinators from -5°C to 3°C
Normal germinators from 3°C to 11°C
Warm germinators from 11°C to 30°C
Hot germinators above 30°C

Use the germination temperature information in the plant information to plan the best time for sowing.

Practical tips

For seeds to sprout reliably and vigorously, they need not only water and light, but above all a stable, adjusted temperature.

Large differences between day and night, such as those that can occur on a windowsill or in an unheated room, significantly disrupt this process.
Direct sunlight on seed trays or plant pots can also cause temperature spikes.
Cold stress leads to delayed germination or fungal infections due to excess residual moisture.
Heat can cause the embryo in the seed to die prematurely or lead to uneven growth.

It's especially important to ensure stable conditions indoors or during pre-growth. Heat mats, mini-greenhouses, and thermometers are reliable tools for this. Shading also helps regulate the temperature outdoors.

The right temperature is more than a detail—it's the key to successful plant cultivation. Those who understand and take it into account will be rewarded with strong, healthy plants. Those who take temperature control seriously lay the foundation for a healthy and bountiful harvest.

Water

During germination, water is the source of life. Without sufficient moisture, even the most vital seed remains inactive, even though all its genetic makeup for development is already present. It is the essential trigger that brings the seed out of "sleep mode."

What happens when it comes into contact with water?

When the seed absorbs water, its tissues begin to swell, officially marking the start of the germination process. This activates special enzymes in the water that convert stored reserve substances like starch into usable sugar. Through energy metabolism, the seed begins to release energy to enable cell division and growth. The water softens the hard seed shells so much that the root can break through them.

How much water is ideal?

The right amount of water is crucial for a plant's growth process. With insufficient moisture, the plant's metabolism remains inactive. Excessive water compacts the soil, thus promoting oxygen deficiency and the growth of mold. With optimal watering, seeds germinate evenly and develop steadily and healthily.

Stratification as a germination aid

To help plants adapt optimally to environmental conditions, we can use another method to support plant development - stratification.

Stratification is a method of placing seeds into a dormant phase to promote germination of specific species. This artificially mimics natural cold or warm periods. We distinguish between two types of stratification:

Cold stratification - for seeds from temperate climates
Warm stratification - for tropical or subtropical plants

The cool temperature can be created by a refrigerator or freezer and overcomes seed dormancy in cold-germinating species.
To simulate warm temperatures, the seeds can be placed in warm rooms or heated greenhouses. A heat mat is also an option for overcoming seed dormancy in warm-germinating species.

With both methods, the seeds must be stored for a period of several days to months, depending on the species' specific characteristics. Detailed information can be found in our variety information.

Understanding the specific needs of different types of seeds regarding light, oxygen, temperature, and water is essential for successful cultivation and plant development. Proper care can create optimal growing conditions for healthy plants.