He tweeted Friday from his summer home in Maine about how she liked to help others, and he thanked those who are carrying forward her work.
"She loved helping others and did so with a joyful heart. Knowing there are so many out there who share her passion puts joy in our hearts," he wrote.
Her daughter-in-law, Margaret Bush, marked the occasion by doing something Barbara Bush enjoyed: She read aloud to young patients at The Barbara Bush Children's Hospital at Maine Medical Center.
She joined in cutting a birthday cake after reading "One Fish, Two Fish, Red Fish, Blue Fish" by Dr. Seuss and "Circus Ship" by Chris Van Dusen.
In Kennebunkport, the Bush family had a quiet dinner at home. Former President George W. Bush, the couple's son, was among the participants.
Next week, George H.W. Bush celebrates his own birthday, his 94th.
The two were married for 73 years. Barbara Bush died April 17 with her husband at her side in their home in Houston.
Copyright 2018 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.