If you are not planning on moving in the next 10 years, I would plant them 4 feet apart. That will allow 2 feet from the center of each plant before they enter the others space. These are both double flowers which when well grown are likely to need some kind of support to keep the blooming stems erect. Al

I have these two in my garden and they are both approx 3' tall x 3' wide with huge blooms, that need support. My Festiva Maxima blooms are at least 8" and several plants have 45+ buds/blooms.

Does anyone grows peonies in Houston, TX? And what varieties can survive our summers? Thank you.

Alba, try making a new post.

I grow both FM and SB. FM gets huge -- 4 ft + tall and the blooms are also gigantic. It always needs rigorous staking but looks and smells great. SB is a bit smaller with nice flowers but for me they are very weak-stemmed. They are best for cutting,IMHO.

I am now Interested in single peonies that don't need staking!

Alba, I've seen several posts from people in FL, zone 9, that grow tree peonies and Itohs but don't remember seeing anyone post about Houston. You might want to do as Jayco suggests and start a new post with Peonies in Houston? or something like that in the title so anyone with experience will see it and answer. My closest experience is a friend that grows them in Jefferson, TX, way north of you.