The germination and growth of seeds is a fascinating study. Seeds certainly look lifeless, yet within their hard shells, they are only resting, waiting to resume growth. Seeds vary in their ability to germinate and grow quickly. Gardeners need to understand the needs and growth patterns of individual seeds to choose and care for them.
Seeds are "embryonic plants in a resting state," according to Texas A&M University. A seed contains the endosperm (food), a cotyledon (seed leaf), plumule (shoot) and a radicle (root). The seed is enclosed in the testa, or seed coat. When a seed begins germination, the leaves absorb water and swell. The radicle or root pushes out of the seed coat, followed by the plumule.
Plants grown from seed are much less expensive than nursery-grown plants. Generally, a more varied selection of plants are available by seed than nursery stock, especially heirloom vegetables and tomatoes. Additionally gardeners interested in organic growing methods can start with organic seed and monitor the entire growing process, ensuring that the plant is truly organic.
Some plants, such as lettuce, broccoli, radishes, marigolds and sunflowers, grow very quickly from seed and reach maturity in one growing season. Others, such as tomatoes and peppers, are slow to grow and must be grown from nursery plants or started as seedlings indoors. Perennials take a notoriously long time to grow and most gardeners opt to start these from plants.
Not all plants transplant well, and are better off sown in the ground. Pumpkins, squash, carrots and cucumbers fall into this category. Additionally, many plants, including most fruit trees, don't grow true to the original plant. They may produce foliage and no fruit or fruit with undesirable characteristics.
The three main considerations for seed germination are water, light and temperature. All seeds need moisture to germinate. The moisture softens the outer shell of the seed. Plants vary in their need for light to germinate, advises North Carolina State University. Some seeds, such as lettuce, impatiens and petunias, require light. Others, such as annual phlox, verbena and calendula, germinate best in the dark. Many germinate in light or darkness. Seeds also vary in their need for warmth to germinate. Many vegetables, such as tomatoes, green beans and pumpkins, need temperatures between 60 and 80 degrees F for best germination. Additionally, some seeds may have tough outer shells that require scarification, or softening. Many plants have a shell that is softened after it is eaten by an animal. The acids in the animal's stomach soften the seed, preparing it for germination.
All seeds die eventually if not germinated, but the length of time they remain viable varies depending on the plant, as well as conditions. Seeds should be stored in a cool, dry place to increase length of viability.