Stages of Seed Germination
Seed germination is the way most plants reproduce.
Some reproduce via an underground root or tuber system, but for the most part, seeds will be needed to start growing any type of plant or tree.
Even a mighty oak tree starts from a seed (called an acorn) that is about the size of a quarter.
Seed germination starts under the soil level in the dark, while above ground it appears as though nothing is going on.
Some plant seeds germination quickly and begin to show signs of development above ground within three days, others may take up to two weeks before visible signs of life appear.
It will require patience to start plants or trees from seeds and if you know the stages of seed germination, the waiting will be much easier.
As long as seeds are in a packet or bin on a shelf, they will not germinate.
Seeds must be planted in soil (or similar medium) in order for the growing process to begin.
The ability to keep seeds without them sprouting allows gardeners to reproduce specific heirloom vegetables from decades past.
After the seed is planted, it needs to be watered so the first stage of germination can begin.
Once the dry, hard seed absorbs water it softens and cracks open.
The absorbed water also activates a growth protein within the seed and causes an initial root, called a radicle, to develop and grow downward to anchor the seed and search of more water.
When enough water is absorbed, sprouts (also called shoots) will begin to develop on the top of the seeds and grow upwards.
The sprouts are the first visible signs of underground plant life. Sprouts are very tender and weak, if the soil has developed a hard crust on top or an animal steps on the weak sprout, it probably will not survive.
Increase the survival rate of tender sprouts by spreading a light layer of organic mulch over a seeded area and keep pets from walking on the area.
The temperature of the soil will determine if the seed germinates, rots, or remains dormant.
As a rule of thumb, most vegetable seeds will not germinate if planted in cold soil.
That’s why it’s important to wait until air temperature rises to above 50 degrees for three consecutive days in the spring prior to planting cool season vegetables.
For warm season vegetables, the air temperature must rise to above 70 for three consecutive days prior to planting seeds or the seeds will rot in the ground.
Many gardeners who start their seeds indoors in late winter place the seed trays on a heating pad or under a heat lamp to keep soil and temperature warm enough for germination to occur.
There is also the flip side to the warm soil germination process- some grass types won’t germinate unless the seeds have been exposed to cold temperature for a few weeks and other types won’t germinate unless they have been exposed to the heat of fire.
All seeds must go through period of cold temperatures in order to be viable. It’s a process called stratification.
Seed dealers and home gardeners alike must allow plant seeds to dry and ‘chill out’ for several weeks during the winter in order for them to be viable for planting.
A similar sounding word, scarification, is something which must be done to seeds that are difficult to germinate.
Seeds with tough shells, like beans or peas, must be pierced, filed or cut to break their dormancy and help the seed absorb water after being planted.
Test seeds for viability with this quick test – Place a few seeds on one end of a sheet of paper towel.
Fold the paper towel in half and sprinkle with water until paper towel is moist. Place in a safe, warm location and keep paper toweling moist for three days.
At the end of three days, unfold the paper towel and check seeds for signs of life.
The seeds should be swollen, cracked and a radicle root visible from the bottom.
Once the sprout is visible above the soil, it will continue to grow towards its light source.
For straight, upright plants, the light source must be directly overhead most of the time.
Sprouts will grow sideways if the light source is not overhead.
They will also become tall and leggy (long stems with few leaves) and turn yellow if not provided with enough light.
The better light source, either natural or artificial, the better leaf development the sprout will have.
The sprouted seed may become visible on top of the soil as the germination process continues.
As long as the roots are still intact with the soil, there’s nothing to be concerned about.
If the sprout has been uprooted, gently scratch a little soil back over the roots (leaving the green sprout above the soil), water well and the roots may re-connect back into the soil.
Two tiny leaves will appear on the newly sprouted seed.
These are not true leaves (cotyledons) and are there for the sole purpose of providing as much energy to plant as possible.
These first cotyledons will be larger than the first two true leaves and they will shrivel up and fall off after the true leaves appear.
The next set of two leaves are called ‘true leaves’ and the sprout now becomes a seedling (sapling if it’s a tree).
The true leaves begin to manufacture food for the developing plant so it can continue to grow and produce more leaves.
When the set of true leaves develop on a plant it’s strong enough to be transplanted and/or not be coddled quite so much.
When the water, light and temperature needs of the plant are met, it will continue to grow taller and develop more leaves until it reaches maturity.