Translation:Flowers are pretty.
きれい is not really "clean" in the same manner, is more similar to sparkly, radiant, something that makes your eyes feel good and pleasant. "Clean" in English is more about removing the filthiness from something, while きれい in Japanese is more about describing the thing as something you want to see.
Taking that into context, would you really describe a flower as clean? I think the way a flower can be described as a "a sight for sore eyes" is to make it beautiful, not only by keeping it clean, but by treating it well from the start, by making it grow healthy and strong。きれいな花 in google images gives you a better idea. Remember that different languages express things differently. Sometimes you will definitely want to translate きれい as clean, but it really depends on the context.
「きれいな服」"clean clothes" or "nice clothes".
「部屋をきれいにしました」"I cleaned the room".
「これはとてもきれいな部屋ですね」"this is a very lovely room isn't it?".
Obviously きれい is the same word in all the sentences, but it can be translated differently depending on context because the meaning is different in both languages.
Thanks! The only explanation I've had in the past for "kirei" is that it means "clean" or "pretty" so I treated it that way, and this led to confusion such as "What if something is clean but not pretty? How would I describe that?" Thank you; this is the most clarity I've ever had on the word. That said, I feel like I still don't understand it as well as I'd like. If you can, could you please elaborate further? I get that the essence of the word is more "it looks good and is refreshing to see" (so in "I cleaned my room" I think it's more like "I made my room the opposite of an eyesore," essence-wise) but what about a word that is more true to the English "clean?" Or anything else I'm not understanding on this word yet? (There's a high probability that I'm not even sure what's missing from my understanding, but something is definitely still missing.)
掃除【そうじ】and 清潔【せいけつ】are closer to that meaning of cleaning in English. But the first one is often used for the activity of cleaning, and the second one has some sort of industrial feel, like you can describe a hospital as 清潔な病院 but is more natural to use きれい to describe a clean room.
That said, I feel like I still don't understand it as well as I'd like
I don't think you need to worry. You will see the word and you will see how they use them. There is really no way to understand these other that exposition from the language.