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Germination

New SeedlingsGermination is the process, or ability, of a seed to become a plant. In other words, when you put a seed in the soil mixture and it pokes thru the top of the soil and spreads its leaves, the seed has said to have germinated. To germinate, a seed needs heat and moisture, but no light (its underground and light can’t reach it anyway). So warmth and moisture are the key elements to successful germination. However, once the seed starts to form leaves, it then requires light to continue growing. This is why most gardeners simply add lights right away to newly planted seeds, because they will be needed soon enough and increase the warmth around the seed area.

In general, if you purchase new seeds, you will normally have no trouble with their germinating ability. If you store old seeds however, this can become an issue, especially with seeds several years old. A seeds viability is its ability to germinate. Viability tends to decrease with the age of the seed. Some advanced gardeners will place seeds on a wet paper towel, roll it up, and wait to see if the seeds germinate. This is okay, but because seeds tend to be cheap, and life short, we simply put the seeds in the seed trays and say a short prayer.

How a seed germinates…

Hypogeal Germination

Pea Seed

The seed is placed into warm wet soil, and the seed absorbs the moisture. The seed softens and then splits from the water absorption.

The first item to emerge is the radicle, which is the embryonic root. The radicle will always grow downwards, no matter how the seed is positioned, and will become the roots of the plant.

Emerging Plumule

The next item to emerge is the plumule, which is the embryonic stem and leaves. The plumule will always grow upwards and will become the stem and leaves of the plant. In certain plants, such as beans and tomatoes, the cotyledon also heads towards the suface right along with the plumule (see Epigeal Germination below); in other plants, such as peas, the plumule goes up alone while the cotyledon remains underground, known as Hypogeal Germination. Up to this point in time the seed draws upon the nutrients stored in the cotyledon (endosperm) to sustain it’s growth. The picture to the left shows a pea plant, where the cotyledon remains underground.

Immature True Leaves When the plumule breaks the surface of the soil it forms small true leaves, not the cotyledon, or seed leaves.
True Leaves When the radicle forms small rootlets, the seedling begins to draw it’s nutrients from both the soil, in the form of mineral salts thru the roots, and from carbon dioxide thru the true leaves. The seedling now becomes a plant, some of which are capable of being transplanted outside even at this early stage.

Epigeal Germination

Bean Seed

The seed is placed into warm wet soil, and the seed absorbs the moisture. The seed softens and then splits from the water absorption.

The first item to emerge is the radicle, which is the embryonic root. The radicle will always grow downwards, no matter how the seed is positioned, and will become the roots of the plant.

Emerging Cotyledon

The stem of the plant, known as the hypocotyl, now emerges, but the cotyledon still remains underground.

Cotyledon Leaves The cotyledon now emerges and forms the cotyledon leaves, also known as the seed leaves. This tricks many gardeners into thinking that the seed has now germinated into a plant. Not quite yet! The seed is still a seedling until it forms its first true leaves, not the immature cotyledon leaves pictured at left. Somewhat later, the plant’s first true leaves will appear above the cotyledon leaves.

The picture to the left shows a bean plant where the cotyledon raises above the soil. Rabbits, mice, chipmonks and whatnot love to eat the cotyledon at this point because it is full of nutrients that the seedling uses as food energy. It is like a peanut for the animals – a real treat – and is why many plants are lost to birds and animals at this stage in their development.

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