Hello, Di.

A couple suggestions...

A number of people I know have given scratch off lottery tickets to elderly parents with great success. If you have enough siblings/friends/relatives you might actually give him 78, one for each year. It'll keep him busy for quite awhile and maybe he'll win something. Of course, if his macular degeneration is really bad, he may find this very frustrating... you'll have to judge that.

Or, what about an outdoor outing or picnic to somewhere he hasn't been to. Since he likes to garden, maybe there's a botanical garden nearby. I took my mother to a zoo when she was in her mid-seventies, and she loved it!

Good luck.