Since this word has okurigana (hiragana attached to the kanji) you know that it's probably going to be the kun'yomi reading. You learned this reading with the kanji, but here's a reminder mnemonic to help you:
You are going to spread something. What are you going to spread? How about your arms, so that you can fly into the sky like the super hero that you are! Most heroes can fly when they spread their arms wide!
It was water that spread the virus in Japan.
Three adults unfolded a blanket.
As soon as I went inside, I opened the book.