Plant IQ

Do you know how smart plants are?

Here's some insight into plant IQ for all our plant nerds out there.

What comes first, the leaves or the roots?

How excited do you get when you plant a seed, and after any amount of time, the leaves pop up? I germinate a lot of seeds at the nursery and I’m still elated every time. I often announce their birth upon notice to whoever will listen, and sometimes it’s only me; “You’re here!”But what truly happens for those leaves to pop up? Inside the seed are the baby leaves (cotyledons) and a root, some food and a bunch of hormones. In the right conditions, hormones induce the root to break the seed open and start drinking water. The root is fed by the food inside the seed, as it expands and takes up nutrients from the soil and more water, it begins to feed the leaves.At the right time, the leaves pull themselves out of the seed. I like to see the seeds in this stage, some plants look like they’re bowing as they are born, entering life with reverence. The sunlight catalyzes the baby leaves to start photosynthesizing, and this begins the cycle of energy exchange in the plant. Quite an exhausting journey for 2 little leaves to show themselves!

At this stage, how does the plant know to keep growing straight up?

Why does it grow straight up? It’s a baby and that’s what babies do. Oversimplified, yes. If the top of the plant is the apex, then there is an apical dominance exerted hormonally and proximally by the plant.

Ok, plant nerd break it down: The plant grows straight up because of specific hormones dominating the top of the plant. As the plant grows taller, there is less apical hormonal effect on the lower leaves and a different hormone kicks in and says “Hey! No more Apical Dominance down here! Let’s make side shoots!” And branching occurs.

Think of broccoli. Broccoli knows it’s growing straight up and it’s going to make a nice big flower head, so a hungry farmer can eat it, that’s all catalyzed by plant hormones. But what happens when you cut that broccoli head off? You get side shoots and smaller heads of broccoli. This is an amazing thing about plants: They follow patterns.

Take hibiscus. They’ll just keep growing their little hearts straight up to the heavens 20ft if you let them. Let’s face it, we want a bush, not a palm tree. Tell him (your leggy branches) he’s not gonna grow that way. Snip snip boom. Branching occurs.

What am I trying to teach you guys here? We can break apical dominance simply by cutting the top off. No need wait for the plant grow tall and make branches itself. Just cut it. The plant will thank you and you’ll be happier with the look of it.

Hold on now, some of my plants have fallen over and started growing roots out the side. It’s definitely planted sideways now. Ugh, I hate crooked plants. The bane of my existence. I thought you said only side shoots can grow off the stem, how come roots sunk in? Well, there’s another hormone at work here, and it’s expressed in the absence of light.

The truth is, axial buds (the birthplace of side shoots) look the same for both roots and shoots. The hormones are triggered by the absence or presence of light to make the appropriate organ. That’s why when your plant tips over roots appear. That particular bud saw darkness.

So wait, that’s why it rooted itself, but how did the plant turn its head and start growing straight up again, after it’s been tipped over? How come it doesn’t grow sideways? Is that apical dominance again? Well, yes and no.

There’s another hormone at work here, and the action it’s responsible for is phototropism. That’s the direction the plant grows towards the light (photo=light). It responds to light much like gravity pulls the roots down-this is a different hormone, it’s responsible for gravitropism. Once your plant has that crook in it, you can try and straighten it out, you can cut it, or you can leave it and enjoy its new character. Call it bonsai. Call it annoying and plant the darling straight because they can’t really straighten themselves! Just remember, if you cut it, you’re breaking the apical dominance and you will get branching. But that’s what you want right?

Plants are amazing.

I have barely skimmed the surface of how and why they grow the way they do. Here’s a little-known fact (as if I haven’t already loaded you with plant nerd info): When a leaf is born, it has the same number of cells that make up the entire leaf’s life. None are replaced, none are duplicated/replicated. The leaf gets bigger solely by cell expansion or stretching acted by water. Pretty cool huh? Four years studying plant physiology, anatomy, and morphology at college and I just happened to retain this one little fact. Amazing I know.

So what does come first, the roots or the leaves? Actually, they’re both there, it’s just waiting for the right conditions ?

This article was written by Holly, Senior Sales Associate at Kauai Seascapes Nursery.