I got a sneak preview of what it's like to lose cognitive function after neurosurgery all those years ago... short term to long term memory transfer relies on the frontal lobe being able to "place" the new memory in an orderly manner. Problems happen when the brain can't hang on to the memories long enough to make the transfer, or when the memories get stored in a disorderly manner. When it was explained to me, I made the analogy of "instead of putting the memory in it's right place on a shelf, the brain opens the door and throws it into the room". Which means the memory is there, but hard to find.
An external "marker" such as someone reminding you or a written note in a diary can act as a link to the misplaced memory sometimes. And the act of writing it down can help put things into neurological order. So having a clipboard (or tablet?) with a checklist for garden jobs might help. "Mowing- yes/no. Areas to avoid- _____" "Garden waste to collect-yes/no. Details____" Once written down, he may never even need to refer back to the list, but if he does, it's right there. Am not sure whether the physical act of writing might be more effective than an electronic checklist.
