I often read that you are only supposed to transplant plants at certain times. Well, I've moved irises around in the spring, summer and fall. And when I bought my first [and so far only] home five years ago, I dug up every bulb I could in my rental cottage to take with me. And boy am I glad I did. The four feet tall magenta asiatic lilies bloomed that summer and I have never found these again in the big box stores. I also haunt the clearance racks of Lowe's regular and have gotten such great deals that I didn't care what month it was when I had to plant it. For example, I got a lovely white rose standard for 75% off at the end of last october and planted it immediately afterwards... and it's doing just fine as the central focal point in the center bed. Can't wait to see it bloom for the first time this spring!
Pictured below: Transplanted lilies and larkspur. All doing just fine in their new homes. Got dirt? Will fill!