Do you capitalize first letter in a sectence haiku?

You don't capitalize the first letter of a sentence in a haiku, even if it's the first line. Haiku follow their own rules:

* Syllable count: 5 syllables in the first line, 7 in the second, and 5 in the third.

* No rhyme: Haiku don't rhyme.

* Focus on nature: Haiku often explore nature, but this isn't a strict rule.

Because they follow their own internal structure, they don't adhere to typical grammar rules like capitalization.