Hi there! 

I think the mutated strawberries are partly from gem interference and partly from natural selection. The Earth-science explanation is lies in the way Pearl described the field back in Serious Steven.

We get the impression that everything the battle completely decimated whatever life was living on the fields. But there is some benefit in the overturned and trampled up soil. There’s a possibility that all the fighting unearthed old topsoil and brought more mineral-rich soil to the surface. 

When the battle was over, the gems left the fields totally untouched, and if Pearl’s efforts in Buddy’s Book were any indicator, the CGs also stopped humans from entering old gem spaces. Some species, maybe small mammals or birds which ingested strawberries, that chanced across the field, would, as living things do, deposit the seeds of the berries they’d eaten.

Left alone, with lots of space to grow and no competition, the strawberries could easily grow huge. In the same way insects that were around during the time of the dinosaurs were huge, some spanning up to 2 feet, because they had no natural predators that readily preyed on them.

Given the emptiness of the fields, and how we see only butterflies when Steven first visits, I doubt the strawberries had a lot of competition. From there, natural selection would work its course over thousands of years. Pollinators may have favoured larger berries, as they were more eye-catching, and succeeding progeny would be larger and larger.

Where I think Gem influence comes in, aside from digging up the soil, is in the light that was unleashed by the bomb. We know that sunlight is what kickstarts the photosynthetic process, and that gems can produce their own light. The light we see may have switched the plants’ photosynthetic gears into overdrive. Evidence of this is that, strawberries grow on vines. But in the show, the strawberries are seen growing on very lush and thick bushes. 

More foliage means more sites for photosynthesis, speeding up the growing cycle of plants. And that’s we notice in a lot of gem-only locations, like in Island Adventure, where the plants are huge compared to the people. 

As to why this is happening to only gem-restricted areas, I’d point to human beings as competitors. 10,000 years ago, early man first switched from hunting and gathering to food production. That means by the time war broke out, over 5,000 years ago, people were already farming. 

Our crop cycles, consumption, and conversion of agricultural land into residential areas would have severely limited the super-growth of plants the way they did in non-human inhabited areas.

I did notice actually! I thought it very interesting. So I decided to dissect the evidence we have of the mysterious fusion from Historical Friction. 

I think the bottom-line though, is that in all these accounts, we’re reminded that these are all representations of the past. By no means do they assert to be the absolute or most accurate truth. 

In Historical Friction for instance, one of the first things established is that Jamie and Steven don’t have the resources for a big-budget production. That’s why they make use of silhouettes and party-hat noses in the first place. Jamie doesn’t even change costume through all that.

And from the get-go the silhouettes aren’t even completely accurate. Jamie knows who the Crystal Gems are. Even if he doesn’t know them very well, he has the general idea of what they look like, and that guides the shapes he makes. The same can’t be said for the monster and the Giant Woman. For instance, the “monster” looks a lot like the Mother Centipeetle from Gem Glow.

Source: SU Wiki 

And at the same time has tentacles? These are really odd things to see hobbled together on a corrupted gem but make sense when you take into account pop culture depictions of monsters in the ocean. So it’s not only the script but also his own experiences and understanding that Jamie is drawing from. That’s why we can’t completely trust his image of the Giant Woman, because text translates differently depending on who’s reading it, and also whether the resources for visualising it are available.

In Buddy’s Book, again, one of the first things we’re told is that all this is happening in Steven’s imagination. For instance, I don’t think Buddy really started thrashing on the ground in the Kindergarten. He was probably really dejected and sad, but Steven was embellishing the details as well. There’s also a very small chance that Amethyst actually sounded the way she does now centuries ago, but again, Steven is imagining that because it appears Buddy didn’t record the conversations verbatim, but rather after the fact, including his insights and impressions. So it wouldn’t be too far off to assume that he simply didn’t imagine Rose in period attire, even though she had a coat and hat on in the portrait in Amethyst’s room. Because Rose has a special place in Steven’s mind. In it, she is timeless and she’s a particular unchanging image. He might not even feel right dressing her up the way he did the other gems.

But you’re both right in noting that Steven didn’t seem to address Rose the same way he did the other three CGs. And I think this lies in what we saw from Historical Friction. When the ship saw the Crystal Gems, in the silhouette were Garnet, Amethyst, and Pearl. There was no attempt to even cobble together a Rose-shaped shadow, likely because that wasn’t in the account Pearl wrote. So it would be consistent if Buddy’s knowledge of the CGs was limited to those three.

Later in the desert, he doesn’t refer to Rose as a CG either. He calls her giant woman.

Source: SU Wiki 

To me this indicates how committed Rose was to staying out of the lives of humans. She didn’t interfere in the Captain Dewey fiasco by choice. 

But to me, this doesn’t rule out the idea that Rose was not part of the Giant Woman fusion that saved the ship. If there’s one thing we know about Rose, it’s that she wanted to help people. She loved humans and Earth, even if she didn’t fully understand what that meant at first. She wouldn’t have wanted to see them suffer. In that regard, it’s still possible that Rose was part of the fusion.