I would divide in very late summer or fall. They have roots that are very brittle, so be careful. I have read that those roots can form plants on their own, but I have received some in trade that did not. When I divided mine, I made sure to get a bit of the main plant with a good amount of root & they never noticed being moved. A couple of years & I had 3 plants as large as the original.

It would be helpful to know what kind you have. Are the leaves smallish and fernlike? Does it bloom most of the summer? If yes to both, then what you have is probably the Luxuriant. They are a bit more temperamental than the other kind, they don't get as big as the other kind (see below), and they have very different root systems. Best to get a book to see pictures so you can properly identify it - try looking it up on www.bluestoneperennials.com, or "google".

If it has larger leaves, shaped more like maple leaves than ferns, and blooms its head off and then gradually diminishes the blooming and stops altogether by around the 4th of July, it's probably the Spectablis or old fashioned kind. Even though yours doesn't die back in the summer, based on the size of the plant, I would say the old fashioned kind is what you have. (Some of them don't die back, especially if the soil is moist and it's mostly in shade, and they can get to be shrublike in size).

The old fashioned one has a root that's a big solid mass, like a potato, or a piece of fresh ginger, only bigger. That mass is very brittle - pieces of it can break off (and probably will when you dig it up). To divide, wait until fall when you're sure it's done flowering and the foliage has begun to decline. Dig it up with a shovel, lay it on the ground, and cut it into pieces - the bigger the piece, the bigger the plant will be when it comes back in the spring. Plant each piece in at least partial shade, water well, and you'll have new plants in the spring.

These are very hardy and very easy to multiply this way. I started out a few years ago with one healthy but very tiny little plant that grew to the size of a shrub, and I have divisions of it now planted all over my yard, my neighbor's yards, the Church, the whole neighborhood - it's a great plant! You're lucky to have "inherited" two nice ones!

Had same experience- dicentra spectabilis divides like a weed- chop it in several pieces and plant after they done blooming- now is good time to do it if you going to water it well. It will probably die to the ground after transplant but will come next year. Dicentra formosa or eximia also do divide but better do it early spring- they can sulk a long time.