The forget-me-not is a beautiful flower and one I too use in special circumstances such as this. I made them in icing for the decoraton on my wedding cake and my eternity ring has gold forget-me-nots woven into the band.

I don't know what would grow there Nikki because I live in a different country, but violets grow here under similar conditions that you've mentioned.

Have you thought of attaching a plaque to his rock? That would be so lovely.

I'll leave the rose up to the experts but I also the love the yellow rose. Where I come from, yellow is for remembrance. Maybe Rosemary might grow in there for the very same reason? Just a thought.