More importantly, the hebes stop the herons from landing on the fence before descending to wipe out the fish! The pond is shaded all summer by a large Chinese Silk tree plus the decks overhang each end by about 1m. It is also over knee deep in the middle so temperature is not usually a problem. The water lilies cover a lot as well. It was cleaned out last year (or the year before) so not as much plant as there used to be. The fish were having to use machetes to get through the oxygen weed! It has been very slow to grow back, thank goodness. I shall have a look for some puha. The mint wasn't actually intentionally planted, I had used some soil to pot up ferns which were hung over the far end deck and the mint came up from there!