What makes up new plant growth? Is it dirt?

Common sence tells me that a plant gets energy from the sun threw the photosenthiis process and needs water and soil as a substraight. -But it builds the matter that makes up the new plant growth out of the dirt in the ground. The matter that makes up the soil is changed into new plant matter. However, someone tried to tell me that the plant needs no dirt to generage matter but somehow gets what it needs for this out of thin air. That seems impossible to me. Matter is never created but only changes form. So am I right in thinking that dirt changes to plant matter with the instructions found in a seed?

You are basically correct. However, in addition to water and sunlight, carbon dioxide plays an important part in the photosynthetic process.

What common sense told you? It lied.
Plants take very little mass from the soil in which they’re found. Most of the mass in a plant is carbon taken from C0[sub]2[/sub]. In other words, the person who told you that plants get most of their biomass from ‘thin air?’ Spot on.

“That is precisely the function of common sense, to be jolted into uncommon sense.”

To back up Friedo, wood has a whole lot of carbon in it: you can prove that by charring wood and ending up with charcoal.

The soil within reach of the tree’s roots had little carbon, but the air is continuously flowing through the leaves, bringing CO2 (carbon dioxide) with it.

If much of the mass of a large tree such as a redwood came from the soil, there’d be a hole there.

If by that you mean almost totally incorrect, then yes.

The formula for photosynthesis is

6CO[sub]2[/sub] + 12H[sub]2[/sub]O + light energy —> C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub] + 6O[sub]2[/sub] + 6H[sub]2[/sub]O

I misspoke slightly. Much of the biomass of a plant is taken from the carbon in C0[sub]2[/sub], much of the rest of it is taken from the oxygen in C0[sub]2[/sub]. (Between the atomic weights of the three elements, hydrogen is the wimp of the bunch) The oxygen in H[sub]2[/sub]O is released as 0[sub]2[/sub]

This is, to a certain degree, an oversimplification as IIRC most of the biomass is actually assembled during the dark reaction and involves NADPH[sub]2[/sub] and ATP and protons (H[sup]+[/sup]) which are produced during the light reaction. But it’s been a good few years since I TA’d bio… I may have a few specifics slightly off.

So you are saying that carbon dioxide as a gass changes form to a solid as various plant biomass’s.

Ok, Thats a shock to me. > Then what the heck is in Mirricle Grow then?!
Is it a super dose of carbon?
So by this news, you could grow a plant in styrophome… or jelly… or pudding?
or ANything that could hold it up cause you dont need dirt…
but not grow it in outerspace… or in a vacume… or on the moon…


IIRC miracle grow has its active ingredients as a blend of nitrogen, phosphorus, and potassium. These are often limiting factors in a plant’s enviornment, and represent the trace elements which plants take from the soil. The majority of the soil, however, remains untouched.

Yes and no. Something with decent capilary action so that water can be wicked up is good. Also a medium totally lacking in nutrients would yield plants which were at less than optimal health. Rockwool, for example, is often used instead of soil when dealing with hydroponic gardening. Nutrients are then introduced by being disolved in the water which is given to the plants.

As a caveat, hydroponic gardening is perfectly legal, let’s not get into its illegal uses.

In hard vacuum? No, plants require CO[sub]2[/sub]. Not to even get into the ramifications that a far greater internal pressure than external pressure would result in…

Plants, however, can be grown in outer space.

Here’s a better cite that focuses mainly on wheat

You should be able to find all the information I’ve given you, and quite a bit more, via a quick google search. Google will even correct your spelling for you should you make a mistake.


Miracle Gro is just a general fertiliser. It’s primarily nitrogen and phosphorus with traces of potassium and other minerals. Although most of the mass of a plant is taken form the air the plant still requires mineral elements like nitrogen and phosphorus in order to stay alive. If a plant doesn’t have enough of those elements it simply can’t make use of the energy in sunlight effectively. So although the material in fertilisers makes up a perishingly small part of the actual mass of a plant they are what usually dictates how well a plant grows.

That makes sense when you consider that sunlight, water and air are freely available in most places. Plants have as much as they want. It’s the other things they need that actually dictate how fast they grow.

I suppose you could think of miracle Gro as plant vitamins. They aren’t food in the usual sense, but they enable the plant to utilise food more effectively, much as vitamins do for people.

In theory yes. In practice, no. Plants need to get water and some of those minerals like nitrogen out of whatever they are growing in. And to do that they need to have living roots on the substrate. Plant roots are just like the rest of the plant in that they need oxygen. No oxygen and they will do and so will the rest of the plant. Substrates like pudding or styrofoam are effectively airtight and so won’t support plant growth simply because the rots will suffocate.

Plants will indeed grow in some types of gel, most commonly agar. That’s wuite a common means of propagating plants. However that only works for fairly small plants since the gel is still effectively airtight and roots that go too deep will die.

That’s exactly right.

There’s a branch of horticulture called hydroponics where the plants are grown in nothing but water water with some dissolved fertiliser. For larger plants there is also commonly some sort of inert substrate like stones that serve to support the plant, but the roots never actually penetrate the substrate, the plants grow entirely in water. No soil is ever used.

Well plants won’t grow in a vacuum or near vacuum like that, but that’s because they suffocate rather than because of a lack of building material.

More importantly they require oxygen. A plant in a vacuum would suffocate long before it suffered from any lack of CO[sub]2[/sub].

Quibble. It is, I believe, 3 parts nitrogen, 1 part phosphorous, and 2 parts potassium.
IOW, more potassium than phosophorus.

Good point. In my haste I was focusing on plants adding biomass, but that wouldn’t exactly be a concern w/o oxygen.

Yes, I got the people in the OP mixed up. There’s no need to be a schmuck about it.

I don’t use the stuff. i just buy Brand X, it’s cheaper and it works just as well. That’s my excuse.

Just checked though and the NPK ratio for Miracle Gro lawn is 15:30:15, so mostly phosphorus with equal parts nitrogen and potassium. There appear to be numerous other Miracle-Gro formulations with a range of other ratios.

So although I was wrong I’m going to weasel and say that I meant one of those other formulations. :wink:

Friedo? Pardon?
This not being the Pit and all, I assume you meant the acronym s.c.h.m.u.c.k?
Super Cool Heroic Manly Uncommon Cecilian Knight?

Blake: Good point. I’d forgotten that MG still makes a variety of formulas. The one I had in mind is the one a buddy of mine has been using recently and chewing my ear off about.

In 1648 Joan-Baptista Van Helmont wrote

He almost got it right. The mass of new growth came from the water and the carbon dioxide in the air. Some small amount of inorganic material from the soil was doubtless incorporated, but this amount is trivial.

Oh yeah. The above was excerpted from The Chemical Tree, a History of Chemistry by William H. Brock (W.W.Norton & Company, copyright 1992)

In one of my high school biology classes, they said that the amount of material that a full grown corn plant takes from the soil would fit in a thimble. The soil is important as an anchor for the plant, a source of water, and a source of those trace nutrients. The comparison to vitamins is apt: just as vitamins are critically important to health - you’ll die without them - the trace nutrients that plants draw from the soil, or from whatever medium they’re grown in, are vitally necessary for plants. However, you’ll satisfy your need for vitamins (at least enough to survive) on one multivitamin, while the majority of your nutrition comes from protein, fat, and carbohydrate. Those things are what your body is built from, just like the carbon, oxygen, and hydrogen in water and CO[sub]2[/sub] are what a plant is built from.

That’s an exaggeration. Proteins contain about 16% nitrogen, and plants about 1.5%. With the exception of legumes and other nitrogen fixers, plants get their nitrogen from the soil.