I know you love plants and gardening; you could put together a big beautiful planter for outside their home next spring. You may or may not like the delay factor. The delay and the swapping of DIY for DIY would have the advantage of seeming less like payment for services rendered than a gift card now. But I can also see how a delay might feel uncomfortable, like too much time elapsing without you showing your appreciation. I think it's hard sometimes for someone with a generous spirit to be on the receiving end, but it sounds like your neighbor has a generous spirit as well.