Guess what? You can lighten hair without any chemicals. I know, I know, it sounds too good to be true...and actually, it is. While you can in fact lighten hair with chemicals, it is not consistent among individuals (meaning it could work for someone else, but not you), you aren't guaranteed the color you want, and it could take awhile to see the desired results. But, it's a great alternative if you're not expecting much. I've lightened my hair with both honey and maple syrup (neither intentional).
The most common natural method to lighten hair is with honey. I lightened my hair this way because honey was used in my leave-in, and I didn't realize it could lighten hair so drastically. Honey left my hair this odd, amber brown color. As you can see in the picture, it even looks like a dark blonde (if that makes sense). I stopped using honey because I wasn't so thrilled with the color, and I felt like it washed me out. There are a few ways to lighten hair using honey including with baking soda, lemon, and peroxide. The only thing you really need is water because water activates the peroxide in honey; for me, it was activated by adding the honey to my conditioner. I used it daily because it was my leave-in, but you should see results using it weekly as well (it could just take longer to see results).
I lightened my hair with maple syrup when I was washing with baking soda. I used maple syrup because I didn't want my hair to lighten like I did with honey. Welp, it did, but on the positive side, I actually like the color that maple syrup leaves behind. It's a maple brown (reminds me of the color of maple syrup), and it doesn't actually color all of my hair, but leaves highlights mostly visible in the front. To lighten hair with maple syrup, mix it in water or your conditioner similar to honey, and use, at least, weekly.