If you intend to live where you are now I would expect in the next 10 years your peonies to expand to a width of four feet. Unless they are at least that far apart you could find the lack of air circulation around the plants to cause fungus problems. Planting two feet apart will cause the problem much sooner. Al

I agree with Al. I have made the mistake of planting too close together and lost the mature plant in trying to move. It is better to give extra room where you can plant short lived plants in the space between than loose a valued specimum.

Thanks for the advice. Back to the design board!