Theo, I too, thought of Surtsey when Coffeeelover brought up that it would take thousands of years for vegetation to take hold on a newly formed island.
Here are some pics of how Surtsey is coming alive since its formation in 1963
The volcano-island Surtsey, Iceland. Plants.
Also, your point regarding Adam, Eve and the beasts being created sexually active is well taken.
As per the plants though, to me, there is still some mystery about Genesis. Genesis 2:5 states, "Now no shrub of the field was yet in the earth, and no plant of the field had yet sprouted, for the LORD God had not sent rain upon the earth, and there was no man to cultivate the ground."
We then see that God planted the Garden of Eden specifically for man and the beasts.
This seems to suggest to me that, while the Garden of Eden flourished for Adam, Eve and the beasts, at least for awhile, the rest of the earth was fairly barren. We know that God created plants and trees and such on the 3rd day, not after Adam and Eve.
Some like to point to Genesis 1 and 2 as being contradictory, but really, Genesis 2 is just a far more detailed account of the same story.
But, when we consider those details, we see that there was perhaps far more of a process than our old Sunday School coloring pages would suggest.
When I read Genesis 1:11-12 in the light of Genesis 2:5, I see that whilst God created the earth and created the vegetation for the earth, and created earth and vegetation during the 3rd day, the vegetation was such that it would not support animal life, at least not yet. Thus the need for the Garden of Eden on the 6th day, once the animals and Adam were created.
Which makes me pull back from making any hard and fast statements about what the earth looked like at the end of the 3rd day of creation.
Which also makes me believe that perhaps there is a vast amount of differences between what the earth looked like from those creation days, to the time that Adam and Eve, as well as the animals, left the Garden of Eden.
Which brings me to another point that is often overlooked when considering Genesis, the fact that many times what we think is part of the story, isn't.
For instance, we tend to think that Eve was tempted by Satan fairly early on Sunday morning. The thing is, the Bible nowhere gives us a time-line on how long Adam and Eve and those animals were in the Garden prior to the Fall. People make the assumption it wasn't long, because Eve didn't get pregnant until after they left. But, that is an assumption.
We also do not know how long the earth was in the darkness prior to God stating "Let there be light".
I think about these things, and I think I begin to understand why our earth seems so geologically old, and yet all agree, scientists and creationists alike, that mammals and man are relative newcomers, even if there is disagreement as to what constitutes "new".