Flag Iris are pretty plants, available in all sorts of colours and heights to suit most gardens and colour schemes. But they are harder to grow than you might think. They like a limey soil and full sun, and if you have this, then they will flourish. But then they tend to become victims of their own success, because they spread rapidly. If placed together in the same bed, the more vigorous ones tend to overwhelm the slower-growing ones, and you will, over time, lose the weaker varieties. So they have to be managed.
A successful clump of flag iris will need to be split up every three years or so, as soon as the flowers have all finished blooming. Dig up the clump, break off the growing ends of the corms (keeping 3 or 4 inches of corm and discarding the rest) to make new individual plants. Replant a few, and give the surplus to friends.
Iris tend to exhaust the soil, so when you replant, it's best to find a new spot. If you can't, then re-work the soil with bonemeal (if you can get it), lime (if you need it) or crushed sea shells, and general fertiliser.
There is an Iris nursery in Bubry in Brittany and we went to take a look. It is run by a Mr Chapelle and his partner. They told us they started with 12 varieties, and now they have an enormous field of them for sale. They cross-breed to create new colours, and they showed us some of their results. We chatted about the requirements for successful Iris growing and breeding, and we were shown how to pollinate the flowers.
It was inevitable that we ordered more plants, and Mr Chapelle was good enough to sell us a couple of his new varieties that are not officially available yet. The one shown below I liked for its flash of blue amongst the brown. I shall have to find it a special spot in the garden.
I suspect that I am guilty of having lost a few varieties that we have bought over the years, due to mismanagement. I have photos of all the ones that we have bought, and there are over 30 different ones. I'm not sure I can remember seeing some of them. It's clear I will have to embark on a careful labelling and replanting programme.