I don't know. But I'm guessing it's to do with the shape of the flower. The way some of the petals hang down.

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It is recommended that you always wait for three to agree on a translation.
I speak Connemara Irish, and my input will often reflect that.
I will do an mp3 file on request for short translations.
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Are orchids a bulb plant? That's the only connection I could see to balls.

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I'm a beginner, so corrections and suggestions are much appreciated!
"What? First we give a month to black history, now we're blowing seven days on the Irish!"
Pierce, upon hearing about Green Week

Dictionary says it’s because of the tuber. I wouldn’t have a clue what an orchid tuber looks like, but it’s presumably somewhat testicular in appearance.

‘Orchid’ is based on the Greek word ὄρχις, which means a testicle (and which is actually the same word as Irish uirí). So I’m guessing the Irish name might even just be a calque from English, translating the Latinate/Greek name of the plant into plain Irish—or perhaps just directly translating the older English name of the plant: ‘ballockswort’.

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Not a native speaker.

Always wait for at least three people to agree on a translation, especially if it’s for something permanent.

My translations are usually GU (Ulster Irish), unless CO (Standard Orthography) is requested.