Someone gave me a tree to plant in my yard when my Dad died. We did. A few years later the tree died.

I like some of the ideas on here where it is consciously comforting self or other.

OP, I"m sorry for your loss, and I think it's good to remember a loved on on their birthday.

My grandmother was in our household my entire life until she died when I was 29. After my grandmother died, I always sent my mother flowers on my grandmother's birthday. My mother really liked that. If you have someone else in the family to whom you're close, who was close to your mom, who would be touched by flowers, or a special card and note, or some other treat (that your mom liked) sent to them, thats an option. It spreads the "thinking of her today" feeling around to others.

Since my mom died, on her birthday, I try to watch one of the TV shows she enjoyed. Sometimes I bake a brownie to eat during the show, or make fudge, because she loved and made both all the time. I can't visit her grave on the day, as it's in another state, but if I were able to, I would do that for certain.

Eat her favorite food. Listen to her favorite music. Buy a bouquet of her favorite flowers.