Advice please regarding waterside flowers

Hello all,

I live on a narrowboat. I don't have a garden and even when I lived in a house I confess my wife and I were not avid gardeners. But I've so enjoyed looking through some of the threads on here and I marvel at the passion and dedication of some of you. We also really enjoy admiring gardens when passing by on the canal.

Anyway, to the point of my thread. We have a home mooring in a marina with a reed bed between us and the bank, and I am looking for some suitable flowers to add a bit of colour. Ideally they need to be able to grow in amongst the reeds or at least right next to them. Behind the reeds is a grassed area (regularly mown) but they would perhaps be okay at the edge of that? And once in flower they I'm sure they would avoid them with the mowers.

I'm not good at identifying flowers I'm afraid, but when travelling along in the boat we've seen what we think are Bearded Irises (yellow), and some tall purple/blue flowers which I think are Purple Loosestrife, or some pink ones called Great Willowherb?. I also wondered about Poppies.

Unfortunately there is some criteria needed;
1. I want non-invasive (or not very invasive).
2. Tall enough to show above the top of the reeds.
3. Perennial if possible.
4. Easy to plant (seeds preferred) and I'm happy to wait a while till they show.
5. Low maintenance.

I believe the autumn is the best time to plant? The reasons for numbers 4 & 5 is because we aren't supposed to plant anything as the marina management can be a bit funny about this kind of thing, but if flowers suddenly began to appear next year (or whenever), they wouldn't say or do anything. It's just that I'd prefer them not to see me doing anything. I could get away with scattering some seeds or even poking them down into the ground. It's just any ground preparation that I wouldn't get away with doing.

Perhaps I'm expecting too much but if any of you can be of some help with advice I would be really grateful, and are there any other suitable flowers that you can recommend? Thanks for taking the time to read my thread.

Best wishes,

Bob in Staffordshire