Seeds are amazing. Although they might appear to be tiny lifeless objects, seeds are powerful living things just waiting for the right conditions to do their thing! Each seed contains exactly what it needs and is designed specifically for the job it must do. All seeds have the same mission. To germinate and grow into a plant that will produce more seeds.
It is important for farmers, and gardeners, to understand the science of seed germination so they can maximize yields while efficiently using resources.
So, what exactly is germination? And how does it work? Let’s explore these questions and others.
What is germination?
In simple terms, it is the process of a seed developing into a plant. Germination occurs below ground, before the stem and leaves appear above the soil.
How does germination work?
To understand the process, you’ll need know the main parts of a seed and their function.
All fully developed seeds contain three basic parts, the embryo, endosperm and seed coat. The embryo is the part of the seed that develops into a plant. It contains the embryonic root (radical), embryonic stem (epicotyl and hypocotyl), and one or two seed leaves (cotyledons).
The endosperm contains the starch or stored energy for the developing embryo. The endosperm is the largest part of the seed and packed around the embryo. The seed coat is the outer layer that protects the seed’s internal structures.
The first stage of germination, called imbibition, occurs when the seed is exposed to water. The seed absorbs water though its seed coat. As this happens, the seed coat softens.
Next, water triggers the seed to begin converting starch to sugar. This provides energy for the embryo during germination.
More water is then absorbed and the seed’s cells start to elongate and divide. The radicle, or primary root, is usually the first part of embryo to break through the seed coat. It grows downwards to anchor the seed in place and absorb water and nutrients from the soil.
Next, the shoot and seed leaves emerge from the seed coat. The process and order depends on type of seed. Monocot and dicot seeds are structurally different, which affects how they germinate.
Soon the shoot will emerge from the soil. The seed tissue will diminish as the plant’s roots, stems, and leaves develop.
What do seeds need to germinate?
All seeds need water, oxygen, and the proper temperature to germinate.
The soil temperature must be warm enough so seeds can germinate, but not so hot as to damage the seed. Cold soil temperatures can cause seeds to remain dormant, increasing their vulnerability to diseases and insect damage. Temperature requirements vary between species. Soybeans, for example, need a minimum soil temperature of 50 °F for germination, but 77°F is optimum.
Water triggers germination to start and is needed throughout the germination process. Soil should be moist, but not saturated with water. Some seeds require more water than others. The critical soil moisture level for corn is 30%, while soybeans need soil that it at least 50% moist in order for germination to occur. That’s because beans absorb more water. Beans take in two to five times their weight in water, while corn only absorbs about 1.5 times its weight.
Oxygen is found in the air we breathe, and in soil too! Oxygen is usually on the list of things plants need to grow. However, it’s not always included when discussing germination.
When a seed is exposed to the proper conditions, water and oxygen are absorbed through the seed coat and cause the embryo cells to enlarge. If there is not enough oxygen present, germination may not occur. The most common reason for a lack of oxygen is too much water in the soil due to over-watering or flooding.
Do seeds need light to germinate?
Sometimes, not usually. Most seeds do not require light for germination and germinate best in dark conditions. However, some seeds like carrots & some lettuce varities need light to germinate. The stimulus of light causes them to break dormancy and start germination once exposed to water and proper warmth. These seeds germinate best when planted on the soil surface or just barely covered with soil.
Why does planting depth matter?
Although it may be tempting to plant seeds shallow so they emerge sooner, it is important to follow the recommended planting depth. Planting too shallow can result in insufficient soil moisture for germination or a weak root system. Planting seeds too deeply causes them to use all of their stored energy before reaching the soil surface. Like temperature and moisture, ideal planting depth varies by plant species. As a general rule of thumb, larger seeds can be planted deeper because they contain more stored energy to reach the soil surface than smaller seeds. Farmers consider other factors like soil type, planting time, and temperature when deciding how deep to plant.
Nearly everything we eat and most of what we use would not be possible without germination. Vegetables, grains and fiber crops are grown from seed. Meat, eggs, and dairy products come from animals that were fed seeds or plants that grew from seeds.
As you drive past fields of emerging crops this spring, think about the amazing science phenomenon happening before you.