Usual reason for them not flowering is that they are planted too deeply. The top of the bud should be no more than an inch below soil level. They need a period of cold ripening to initiate flower bud development.
It could also be that you are feeding them too well. Many plants do not flower if well fed, especially with high Nitrogen content food. They make leaves instead of flowers.
The other reason for not flowering is if they are planted in too shady a position, they do need sun.

I'd completely agree with Owdboggy. You should see the conditions that Paeonia grow in in the wild - pretty grim, with very impoverished soil, full sun exposure and severe winter cold for the most part. They get over-pampered, over-fed and over-shaded in many gardens and respond by producing luxuriant leafy growth, but no flowers.

I have checked on them and they are not deep at all, so maybe its the feeding I was doing. I won't feed them this summer and see what they do. They look okay at the moment and I can see the new leaves forming so at least they seem healthy enuff. Fingers crossed for some lovely flowers on them this year!