I won't hurt you at all. Your use of repetition from the first line through the remaining three achieves a kind of effortlessness I can only dream of. If nothing else, that is exquisite. As for the rest of the poem, it's narrative is perfectly clear—I really like it.

There is, however, one thing I'd like to bring to your attention.

"realizes with horror"

In my opinion, this is too direct. The dread sense which has permeated throughout your poem doesn't need to be stated explicitly.

when nothing remains he realizes
his garden has no color at all.
there's no help for it.

But of course, that's up to you how you want to keep it. :)