This word is an exception. You'd think it would be the same in Japanese as it is in English, but it's not. And it has two different readings and meanings. Yikes, sorry. Here's a mnemonic to help you out:
Before you read this PLEASE PLEASE REMEMBER this is NOT a jukugo word. It's weird. You're gonna want to type ぎんこう but that's wrong. Stop that now.
When you think of a ginkgo tree think about this: Ginkgos are a favorite nesting place for eagles but evil Mrs. Chou likes to eat eagles AND whole gingko trees. She prefers eating eagles WHILE THEY'RE IN THE GINKGO TREES AND ARE STILL ALIVE. So いちょう. Eagles and Mrs. Chou. And gingko trees. It's horrible to think about. Just like this reading not being jukugo.
The other meaning is the ginkgo nuts themselves. They taste like 銀 (ぎん) naan (なん). Mm mm soft and metallic, but still not the jukugo word though. How sad for you and all Japanese learners everywhere.
Poisoning symptoms develop when I eat too much ginkgo.