Interesting problem, bananafan...
I'm going to take a stab at this problem...the real question is how long the grass will survive (and sustain normal growth/reproduction) without new micronutrients being added to the system.

List of plant essential nutrients (and their needed values in the average plant)+ sources in this system:

C = 450,000 ppm from c02 in atmosphere
H = 60,000 ppm from photosynthetic water splitting
O = 450,000 ppm from photosynthetic water splitting
P = 2,000 ppm Present in rock
K = 10,000 ppm Present in rock
N = 15,000 ppm From rainwater produced by an ionizing storm
S = 1,000 ppm from air pollutants resulting from burning of fossil fuels
Ca = 5,000 ppm common in dolomitic limestone
Mg = 2000 ppm common in dolomitic limestone

All of these are needed in very small amounts, and their absence may not become apparent until late in the plant's lifecycle:
(Also, all are present in small degrees in rock)

Fe = 100 ppm
Mo = 0.1 ppm
B = 20 ppm
Cu = 6 ppm
Mn = 50 ppm
Zn = 20 ppm
Cl = 100 ppm

Grass is a monocotyledon and thus reenforces it's cellwalls with silica...which is also common in silicate rocks.

I hope I'm on the right track...unless this is a trick question?

You can buy the overpriced crap you see on TV that they grow on bricks.

hueylatoani: Wow, I'm truly impressed with your answers. I wish I had such knowledge.

modenacart: Yeah ... makes me think what makes that stuff work.

But, hang on guys, I'll post a picture soon. He he ... sorry to keep you guys in suspense. In the meantime, keep scratching your heads ... :D

Seriously, man, you're killin' me.

ok, here comes the answer .....

Picture of the pot (remember the riddle was NO growing medium IN the pot). Go figure for 1 sec and scroll down for the complete answer.

{{gwi:422899}}

.
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .

The Answer:

The grass grew from the soil underneath the pot, went through the pot opening and up on the surface of the pot. It fooled me for a moment, but because I had the full picture in front of me, it was easy for me to see where it all started. :)

heh-so it was a trick question. I suppose I make things more complicated than they need be-I was envisioning some sort of non-recirculating passive hydroponic array...anyway, it's really amazing how hard some plant shoots will work just to force their way into a space...I remember when I took weed science hearing of a yellow nutsedge (cyperus esculentum) sprout pushing up though the bottom of an above-ground swimming pool. Drained the pool. Cyperus can exert over 2,000 psi of force from it's expanding shoot tip-5 mil black plastic doesn't stand a snowball's chance.

Is it grass? It looks like a daylily.

Yep, weeds definitely have their weed power.

The grass in the picture is St. Augustine. They're really agressive.

Now if the stuff you WANTED to grow would just do that!!!

Holy crap Huey if you don't hurry your going to miss your Mensa meeting.....lol