Just how do seeds grow? Have you ever wondered?
It’s a process that’s worth understanding – at least on a rudimentary level.
The science of seed germination can be very complicated at a chemical and molecular level.
That complex science is really a bit beyond the scope of what we need to know as gardeners.
But having at least a basic understanding of how seeds germinate and grow can be an aid in our gardening efforts.
Being able to answer the question of ‘how do seeds grow?’ can help us in being able to understand what our seeds need to grow, and how important it is to provide them with these essentials.
And the answer to that question is really quite fascinating!
Probably the first step in understanding how seeds grow is to understand what a seed is.
A common misconception is that seeds only contain the building block components necessary for the creation of a new plant. But that isn’t quite true. In actuality, each seed contains a tiny plant in embryonic form. In fact, the embryonic plant in each seed is quite well formed, with the first leaves (called cotyledons) and root clearly visible on a microscopic scale.
Though the little embryonic plant is very much alive, prior to seed germination the embryo is in a dormant resting state – almost like hibernation.
The embryo is surrounded with food that it will use during its first days of growth. This food is called endosperm. Surrounding and protecting the embryo and endosperm is a hard shell called the seed coat. The coat protects the embryo from extremes of temperature, from mechanical damage, and from parasites.
A Tiny Life-Support System...
So essentially, a seed is a life-support system for a tiny baby plant.
How long can the tiny plant survive within its life-support system?
That depends upon a variety of factors, and varies according to species. Some seeds are able to sustain the life of the embryo for no more than a few months. But others may be able to offer life-support for their little occupants for a VERY long time.
In fact, scientists have succeeded in germinating a date palm tree from a seed that was around 2000 years old! Imagine the little plant within that seed waiting patiently for 2000 years for its opportunity to grow. That embryo’s life-support system certainly served it well!
(Interestingly, that 2000 year old seed is of a date palm variety known as a Judean date palm, which has been extinct for centuries! At last report the date palm, nicknamed the Methuselah tree, was 3 years old, 4 feet tall, and thriving. Scientists hope that this tree will help them resurrect the Judean date palm from extinction. For those familiar with the saga of Masada, it’s also interesting to note that this 2000-year-old seed was found during archeological excavations at Masada. It’s thought that the seed was part of the food stores that provided sustenance to the Jewish occupants of Masada during the Roman siege.)
Essentially, the germination of seeds begins when the dormant embryonic plant resumes growing. But before the embryo breaks dormancy, conditions must be right.
Because once the embryo resumes growth, it’s in a race against time for survival. Once seed growth is underway, the embryo has lost the protection of its seed coat, and it begins to rapidly consume the food stores of its life-support system.
What are the ‘right’ conditions that will spur the embryo into giving up the protection of its life-support system, and committing itself to either life or death?
That varies greatly among plant species, but it’s mostly a satisfactory balance of light, temperature, oxygen availability and moisture that will cause the embryo to break dormancy.
Once the chemical triggers have occurred that transforms a dormant seed into a germinating seed, the first outward sign of growth is the root. The root extends downward, anchoring the embryo in place, and providing the embryo with water and nutrients absorbed from the soil.
Next, the stem supporting the embryo leaves, the cotyledons, pushes out of the seed coat and reaches for the surface of the soil.
And this is a critical step in the life of the little plant.
Not Too Deep, and Not Too Shallow...
If the seed is planted too deeply, the embryo will deplete its food stores (the endosperm) before the stem can push through the surface of the soil. Without being able to expose its cotyledons to the sunlight so that they can begin manufacturing food, the embryo will die of starvation without ever ‘seeing’ the light of day.
But if we have done our job properly, and provided sufficient moisture, the proper light (some seeds require light to germinate; others don’t), and we didn’t plant too deep for the embryo to reach the sunlight, then the embryo will have established itself as a seedling.
And its life-support system, the seed, will have done its job.
So the question of ‘how do seeds grow?’ can also be considered as ‘how can we help seeds grow?’
Because by understanding the germination needs for each species of plant in our gardens, and giving them what they need, we improve the chances of success for each seed we plant.
And by doing that, our gardens will be more successful and more fun.