Plant seed growth, or germination, is an intriguing process by which tiny seedlings emerge from dry, wrinkled seeds. There are several phases of seed germination. Water absorption--the first stage--leads to increased enzyme respiration as plant cells are duplicated. When the embryo grows large enough, the seed coat bursts open and a growing plant emerges. The root's tip is first to emerge as it anchors the seed, allowing the embryo to absorb nutrients and water from the soil.
There are two types of germination: Hypogeal germination and Epigeal germination. Hypogeal germination occurs when the cotyledons--seed leaves--are below the soil's surface. A pea seed provides an example of this type of germination. Epigeal germination occurs when seed leaves stay on the new shoot and are brought above ground. Beans and ash trees provide examples of Epigeal germination.
Seed germination is measured in weeks. Seeds taking up to 12 weeks usually result in seedlings that are more straggly and that emerge irregularly. Seeds that take only two to three weeks will usually emerge more evenly.
Essentials Needed for Germination
Seeds grow until three basic needs are met: water, warm temperature and good soil. A seedling depends on the food supplies that are stored inside the seed until it has grown large enough for its own leaves to start making food with photosynthesis. The roots of the seedling push down into soil. The roots anchor the new plant so the seedling can absorb minerals and water from the soil as its stem carries new leaves upward toward the sun's light.
Easiest Seeds to Germinate
Standard garden annuals such as corn, tomatoes, poppies, peppers and lettuce are some of the easiest seeds to germinate. Usually, garden annuals require minimum pretreatment, being able to germinate fairly well using moderate watering and regular soil. However, perennial seeds usually need more pretreatment.
Because some seeds can take longer to absorb water and germinate, it often helps to soak them in water overnight. However, the DianeSeed webside warns not to soak seeds for more than 24 hours, unless instructions on the seed packet recommend otherwise. Soil should also be kept warm for some seeds such as tomatoes and many tropical plants, which also need warm nighttime soil temperatures for germination to occur.
Novice gardeners may think applying too many nutrients to soil poses no danger, but excessive nutrients can inhibit germination. Also, once a seed has germinated, too much nitrogen or other toxic nutrients can burn the roots.
Ideal germination temperatures vary from one species of plant to another. Some seeds require special conditions and treatments--involving temperature, light and moisture--to germinate. For example, a seed with larger amounts of endosperm is able to feed an embryo plant longer as it works its way up toward light, so these bigger seeds can usually be planted deeper.