Hi, do you know which species you have? there are about 250, including annuals, biennials and perennials, and do you feed them, or the soil with manure or fertilizer, as the nutrients are used up, the flowers, and the plants themselves, will get smaller each year, unless they're replaced, try giving them a feed of something like growmore, and see what happens, Derek.

Hi Derekm - I don't know what species they are but they are perennials. I have used growmore. As I said the plants are very large and healthy. It just that the flower heads are very short.

Hi Sadie, try using a fertilizer high in phosphorus, this encourages flowering, and is the second number on the packet of fertilizer, ie, 5 12 5 , Derek.

Thanks Derekm - will try this.