Right now, this suffers from being far too short. Over-pruning, perhaps? Fear not it being too long! Length itself is not a crippling agent. I would like some expansion, please! Specifically, first in terms of plot. For pragmatic purposes, I'll give you some starting points:
Welcome to my garden! My garden is most likely different than a "typical" garden you may see while traveling.
While most people might have hundreds of roses of all colors in their gardens, my garden doesn't grow some of the more popular colors that everyone obsesses over.
Here we have three sentences in two whole paragraphs. We need more!!! Each can be expanded. Also, one might consider the way you tell your allegory. Is it the gardener, taking us on a tour? Have we stumbled here, and are given the information via another medium? Is it directly revealed via narrative? Give us a journey! A plot-pyramid! This is my main issue, and I think by fixing it you will fix length: tell us a story!
Pink roses are almost as abundant as the magenta ones, and often it's hard to tell them apart. Often, these pink roses help the magenta ones grow. They also often grow near the magenta ones.
The meanings of all of these rose types are entirely opaque to us without your list of what they mean at the beginning. I'm unable to understand the metaphor, and I think more plot would also help with that. You need especially prolonged and evocative imagery to convey allegory correctly.
Though this garden may seem weird to you, it's mine, and I'm happy with the roses I've grown here.
While all the previous critique applies, I would caution being too blunt with the reader. One must both give enough for them to understand your allegory and also not beat them over the head with the meaning of the metaphor.
Hope that helps a little! Feel free to ask questions or interrogate me further. PM me again with a further draft, if you deem it fit or think my further inquiry would be advantageous! I would certainly be ready and willing!
—Oli