Guest post by Beate Schwirtlich
What Happens When A Seed Germinates?
The whole purpose of starting seeds indoors is to cheat winter a little.
Ironically, even as we cheat nature, we must imitate her. Light, soil, water, air, and a basic understanding of the process of germination are all you need. Once you know the simple things a seed requires, starting them indoors won’t seem half as complicated.
Seeds are their own energy source, a plant in embryo form. They store energy in a form that is released and used only when water, oxygen, soil, and a close-to-ideal temperature are a part of their surroundings.
Until then, they remain dormant. Germination inhibitors are part of the make-up of every seed. They actually prevent a seed from germinating until its chances of survival are good. Usually chemical in nature (five per cent of seeds are simply waterproof, dormant until their seed coat cracks), germination inhibitors put a seed into dormancy. Without these, a tomato seed, for example, would spout right inside the fruit of the plant that formed it, where there is moisture and warmth, good conditions for germination. Inhibitors give a seed time to travel away from the parent plant, and allow it to overwinter, or be stored, giving that seed the best possible chance to reproduce successfully and to spread. Germination inhibitors ‘wear off’ over time, allowing a seed to sprout the next year.
The seed coat or outside of a seed protects it during dormancy. Hidden inside that coat is the radicle or beginning of a root, the hypocotyl or beginning of a shoot, either one or two seed leaves or cotyledons (the seed’s food supply), and the epicotyl, which will become the first true leaves. The seeds of some plants have a second food supply, called the endosperm. Plants with one cotyledon are called monocots. Those with two are dicots.
Spring like conditions soil that’s wet and beginning to warm up, and longer days and stronger sunlight signal the seed to break dormancy. Light triggers germination of many small seeds, while other seeds germinate best in darkness. Some seeds prefer warm temperatures, others cold. Such differences are a reflection of biodiversity. Simply, plants native to areas with warm conditions produce seeds that germinate best in warm soil, while those native to cold places prefer cool soil.
Know what conditions your seeds naturally prefer, and try to emulate them.
Water does two things to a seed. First, it activates enzymes that stimulate the release of food energy stored during dormancy. Second, it splits the tough seed coat open so that oxygen gets in. Energy stored in the cotyledon ‘burns’ and is used only in the presence of oxygen, powering the seedling’s cells as they begin to divide and grow. This process is called respiration.
Soil holds the water and air that a seed needs to respirate. Too much water drives out air pockets in soil. Don’t over-water. Without air, seeds can’t use their stored energy through respiration. Never let seeded soil dry out. Without water, seeds can’t use their stored energy.
This stored energy only lasts so long. That’s why a sprouting seed works so hard to break the soil and unfold into the light quickly. It’s also the reason that germination of many seeds is triggered by light. If a small seed germinated in a moist but dark environment, it might run out of energy before ever reaching the soil surface. But if a seed needs light, it won’t germinate until it’s close to the soil surface. That way, it has a chance to survive. But before a seed begins to grow up, it grows down, anchoring itself with a root, the first life to emerge from the seed coat. The root allows the spout to begin to absorb water and food from the soil.
A seed can only store so much energy. That‘s why smaller seeds must be planted shallower, larger seeds deeper. Little seeds planted too deep will exhaust themselves and die underground. Large seeds can easily dry up if planted too shallow. Really small seeds should just be pressed onto the soil surface.
Next, the shoot begins to grow, splitting the seed coat even more. Soon, the growing shoot pushes the seed leave(s) above the soil. They unfold, sometimes still wearing their dried up seed coat on their tips. As the root continues to grow, a bud will appear between the seed leave(s). From this, the first two true leaves will grow, enabling the plant to begin to photosynthesis, the production of energy using light.
Lacking light, seedlings will compensate by shooting up towards the light source and becoming ‘leggy’ and weak. Provide lots of light twelve hours a day. Use a south-facing windowsill, or good artificial lighting.