I always forget to maintain my garden, while I enjoy doing it. How can I help myself not to forget?

If you leave the house daily walk through the garden on the way in. Great way to wind down before getting into the house.
Other times, Have a routine you enjoy that you won't miss tied to your garden. Coffee or exercise break? Do it outside.

This is something I struggle with too!! I find the best method is to place visual reminders to do the task in places I am likely to be. My watering can lives near my kitchen sink. When I finish dishes in the morning I automatically fill the watering can and tend to my plants. On days where I need to spend more time working in the garden I like to choose a podcast or audio book to listen to while working.