How Do Big Plants Grow From Such Small Seeds?

Mar 17, 2017

Why are there so many plants? How are seeds made? How does germination work? How can plants grow so big if they start from such a small seed? Why are flowers different colors? Why are plants and trees green? Where does dirt come from? In this episode of But Why, we're talking about plants with garden consultant Charlie Nardozzi.

"How does germination work?" — Miriam, 8, Montpelier, Vt.

"Germination is how the seed starts to grow. That's the basic way to look at germination. Germination starts with the male fertilizing the female, that little embryo gets fertilized and then the seed has a seed coat that protects it. And so for that seed to actually grow, it needs the right conditions. Nature has been perfect in figuring this one out. In a cold climate like up here in Vermont, you have this happening during the summer in the fall and you have these seeds, and they drop to the ground, which is a natural process. It wouldn't necessarily work if they started germinating immediately because it's going into winter and the plant will die. So they have a process where they go into a thing called dormancy, like a sleep."

"The seed is just going to sleep there and wait till the right conditions occur towards the spring. Those conditions will be the right amount of moisture and the right temperature, a nice warm temperature. Those are the two key things they need for seeds to start to grow or germinate. Each seed is a little bit different about what they need and how much they need, but it is usually those two factors. Once they start growing and germinating then that seed coat will break open, the little embryo starts growing. It's almost like a little chicken and egg. The chick starts growing starts pecking its way out of the egg. The same thing is happening with the seed coat. The embryo starts growing and the seed coat breaks apart.

"There's pressure and the seed coat has kind of been weakened a little bit because of the warmth and the moisture. And then out comes the little sprout. And a nice way to watch this actually happen is if you get an avocado pit and you put the avocado pit with some toothpicks on it over a glass of water so the bottom's in a little bit of water and just watch. It'll take a few weeks or so, but eventually that pit, which is kind of like the seed coat, will start breaking apart and out comes the shoot."

Miriam, left, 8, lives in Montpelier, Vt. She has been working in the garden since she was two, and has always been interested in how nature works. Kai, 6, lives in Ottawa, Ont. He loves reading, swimming, and cross-country skiing.
Credit courtesy from parents

"How can plants grow so big if they start from such a small seed?" — Kai, 6, Ottawa, Ont.

"It's amazing when you think of a redwood tree, big huge tree. If you ever see the seed of a redwood, it's tiny, it's small. So how does that all that happen? Inside that seed are things we call genes, and what genes are is like information. It's all this information that's inside that seed and it tells that seed how big it's going to grow, how wide it's going to grow. It's kind of similar to the genes that people have. So you have genes in a baby and those genes will tell you if that baby can have blond hair, or black hair, or if they have blue eyes, or brown eyes, etc. All different parts of what makes the characteristics of that person. The same thing is happening in that seed. All that information is in there.

"Once that seed starts to grow through germination, all that information starts to [be expressed]. And so even though the seed might be tiny, because it has the right information, it will tell it that it needs to grow this big, this wide, have this kind of fruit on it, this kind of flowers, whatever it is.

"And trees keep growing that big because there's a little mechanism in there telling it 'keep growing, keep growing, keep growing.'" 

Charlie Nardozzi, garden consultant.

Listen to the full episode for answers to more plant questions and where does dirt come from?

Read the full transcript.