How can plants grow through asphalt?

[mroek]

Last autumn I had my front yard paved with asphalt. Prior to this I sprayed the area with diesel to kill plant seeds, as I was adviced to do.

However, now I have two lange bulges in the paving, and I'm pretty sure that a dandelion will soon emerge from each of these spots.

The question is how on earth this is possible? It of course means that the diesel did not kill the seeds, but how can a flower actually break through the asphalt paving?

How does it know in which direction to grow? After all, there's not much light passing through the paving? And where does the force to break the paving come from? I realize that this is a slow process, but nevertheless it requires considerable force to actually break the paving.

Anyone have any answers to this? And what can I do about it now?

-Øyvind

[Rob Lister]

Originally posted by mroek
However, now I have two lange bulges in the paving, and I'm pretty sure that a dandelion will soon emerge from each of these spots. [/B]

Huh? Asphalt degrads over time, sure, and assuming you live in a place where dandelions are common, one will emerge as predicted.

IOW, how is that NOT probable?

I'm not even going to ask why you paved your yard. I'm sure you had good reason. I've even contemplated to so meself.

[Earthborn]

Sometimes nature can play magic tricks on you. A plant grows through asphalt and you think it must have broken through. You are probably thinking about it the wrong way around.

I think it is more likely that the asphalt breaks first, and this causes an opening in which a seed can fall. If the ground under the asphalt gives it enough nutrients, it will sprout and the plant will go through the crack, making it appear as if it broke through.

Accidental Magic!

There isn't much light passing through the paving, but then again there's not a lot of light passing through the soil either. And still seeds manage to grow in the right direction, even if they are a few decimeters underground. How they do it? Gravity.

[DangerousBeliefs]

Get yourself a propane torch and a stamping tool (piece of 2x4 or a log will do).

Heat the bulge up until the asphalt is soft.

Stamp it down flat.

Wonders of nature crushed by humanity's need to pave.

[Hellbound]

Pave the whales!!!

[mroek]

Originally posted by Rob Lister


Huh? Asphalt degrads over time, sure, and assuming you live in a place where dandelions are common, one will emerge as predicted.

IOW, how is that NOT probable?

I'm not even going to ask why you paved your yard. I'm sure you had good reason. I've even contemplated to so meself. The asphalt is less than a year old, and hasn't had time to degrade that much.
Yes, dandelions are common here, but the point was *how* they are able to break up the asphalt.

[Earthborn]

They don't break the asphalt. You probably live in geologically active area where the ground moves and breaks the asphalt because that doesn't move with the ground. Then when the asphalt is broken, there is place for the dandelions to grow.

[mroek]

Originally posted by Earthborn
Sometimes nature can play magic tricks on you. A plant grows through asphalt and you think it must have broken through. You are probably thinking about it the wrong way around.

I think it is more likely that the asphalt breaks first, and this causes an opening in which a seed can fall. If the ground under the asphalt gives it enough nutrients, it will sprout and the plant will go through the crack, making it appear as if it broke through.

Accidental Magic!

There isn't much light passing through the paving, but then again there's not a lot of light passing through the soil either. And still seeds manage to grow in the right direction, even if they are a few decimeters underground. How they do it? Gravity. I still belive it does break through. At least the asphalt is quite violently deformed.

Here's an image of one of the spots, from two different angles:
http://personal.dynator.no/asphalt.jpg

That doesn't rule out your theory of the seed falling into a crack, but it shows that the sprout quite violently breaks the asphalt.

[mroek]

Originally posted by DangerousBeliefs
Get yourself a propane torch and a stamping tool (piece of 2x4 or a log will do).

Heat the bulge up until the asphalt is soft.

Stamp it down flat.

Wonders of nature crushed by humanity's need to pave. Yes, that's probably the best way to do it, although I believe I have been told that asphalt will not re-bind when heated. It will get soft, though.

[mroek]

Originally posted by Huntsman
Pave the whales!!! Here in Norway we kill the whales, but maybe we should start paving them?

Good one, Huntsman! :D

[Hellbound]

mroek,

Actually, the spots you see as "breaking through" are more likely the effects of thermal stress. With asphalt this can happen within a few years of it being laid...asphalt is not exactly the best paving material (but it is cheap). However, what happens is the asphalt expands in the summer or when the heat is higher, and contracts when it gets cooler. When it contracts, it creates minute cracks through the surface. On close inspection, one can generally see these hairline cracks running throughout any asphalt that's been there for a few years or longer.

Anyway, once these weak spots are there, the next step is expansion. Summer comes along, temperatures rise, and the asphalt begins to expand. The expansion causes it to deform. Since it can't deform downwards (the Earth is in the way) it bulges up, producing bulges much like the ones in your picture. You'll also see long rows or raised asphalt that are qualitatively identical.

From here, it follows along with what Earthborn is saying. Once any sort of hole develops that gan give a seed access to the ground underneath (or enough nutrients from dirt collected in the crack), a plant will begin to grow. Once the plant starts growing, it can very well speed up deformation in the asphalt. However, this is because the plants will find and us any minute cracks that develop, rather than the plants being able to break through the material.

[mummymonkey]

I've seen this often with various plants. Here's an explanation from the New Scientist (http://www.newscientist.com/lastword/article.jsp?id=lw186). It refers to mushrooms.

The upwards pressure comes from the turgor pressure of the individual cells making up the wall of the hollow stalk of the mushroom. Each individual cell grows as a vertical column by inserting new cell wall material uniformly along its length.

[John Bentley]

Darn it, mummymonkey! I actually had the answer to this question, and you beat me to it! I was taught this in high school (a veeerrry! long time ago) as part of an advanced sciences course. We were discussing the power of hydraulics at the time, and the question was posed by the instructor.

Here's another good question I remember. How does water get to the leaves at the top of a redwood tree? The column of water from the root to the leaf represents a substantial amount of weight. I can't remember exactly how much, but I'll run the math and post it if I get the time.

[Wrath of the Swarm]

It's a combination of osmosis (driven by evaporation and the production of sugars in the photosynthetic leaves) and capillary action.

Dangle the end of a paper towel strip in water, and water will soak upwards, against the flow of gravity. The attractive force between the water molecules and the gaps in the towel are (on a small scale) much more powerful than the pull of the Earth's mass.

[Skeptoid]

Dandelions have a long taproot and will overwinter. About the only thig diesel sprayed on the surface will do is pollute the groundwater. To kill dandelion, you need to use an herbicide that contains salt of dicamba.

[John Bentley]

Originally posted by Wrath of the Swarm
It's a combination of osmosis (driven by evaporation and the production of sugars in the photosynthetic leaves) and capillary action.

Dangle the end of a paper towel strip in water, and water will soak upwards, against the flow of gravity. The attractive force between the water molecules and the gaps in the towel are (on a small scale) much more powerful than the pull of the Earth's mass.

Almost right. Let me preface this explanation by saying that I've just been proven dead wrong about something in another thread that I was sure I remembered correctly from a long time ago, so I'm only going to say I'm pretty sure of my facts. Here goes.

The current theory is called the cohesion theory because it depends on the cohesion of water molecules to each other through hydrogen bonding between the molecules. In a very small diameter tube, the string of water molecules has a tensile strength equal to steel wire. As the leaves transpire water out of their surfaces, they pull the "water wire" up the tubes (called xylem). These tubes are roughly 40 um in diameter. As far as I know, it does not have anything to do with osmosis, or the attractive force between water and the xylem elements (capillary action).

But hey, I've been wrong before.

[shemp]

I don't see anything green coming up through those bulges. More likely just volcanic activity. I would move as soon as possible.

[Iamme]

mroek---The photo looks very much like the bride of Hulk, laying on her back. A possible new movie release to join the brides of Frankenstein and Chuckie :D

[Pyrrho]

Did you use a good asphalt sealant when the work was done? Judging by the photos the asphalt wasn't sealed.

[mroek]

Originally posted by Pyrrho
Did you use a good asphalt sealant when the work was done? Judging by the photos the asphalt wasn't sealed. I cannot recall that they did anything special to the asphalt after they'd finished. The only chemical I saw them use was a kind of asphalt glue they used to make sure my asphalt would bind to the asphalt of the connecting street.

I've never heard of asphalt sealing, but I'd guess it's some chemical sprayed onto the asphalt to seal the pores?

[mroek]

Originally posted by shemp
I don't see anything green coming up through those bulges. More likely just volcanic activity. I would move as soon as possible. Patience, patience. I'm quite sure there will be a dandelion emerging quite soon.
There are no volcanos in Norway, so maybe I'm about to get my 15 minutes soon...? :)