Since you just work outside for gardening everyday, a large hat is enough to protect you from the sunshine because you don't have to see objects far away and the large hat can shelter your eyes and near objects from the sunshine. So you don't have to wear sunglasses if you wear large hat for gardening.
It is good for you to wear big hat when gardening, but the large hat can only block part of the UV rays. It is better to equip yourself with 100% uv protection sunglasses to protect your eyes. Too much UV rays can contribute to causing cataracts and macular degeneration.