A garden is a dynamic work of art – it is always changing, never static. Trees grow and spots that once were sunny become shady. The plants that thrived in the sun are now languishing in the shade. The sun perennials are weakly blooming or not blooming at all. The area you thought was dry, is actually a puddle for most of the summer; and that area you thought was shade actually gets 8 hours of sunshine. It’s time to make a move. Plants in general don’t like to be moved, but done gingerly, it can happen successfully. Then the question then is when is the best time to move perennials?
The rule of thumb for moving perennials is answered best by narrowing down when they bloom so you can enjoy the bloom and move your perennial too. For spring and summer bloomers, savor the bloom, and once they are completely done, it is safe to move them. A few perennials that bloom in spring are Phlox, Poppies, Primula, Pulsatilla, and Saxifrage. Summer blooming perennials include Campanula, Daylilies, Delphiniums, Salvia, Veronica, and Hollyhocks. For the perennials that bloom late in the summer season, such as Fall blooming Sedums and Solidago, move them early in spring so they can reestablish with the goal that they will ultimately bloom.
Be sure to maintain a large clump of soil around the root to minimize shock to the roots as much as possible. Dig a large hole and just fill in where there is extra space rather that peel off soil from the roots to fit the hole. Give your perennial a big drink of water – always water when you transplant & roots are disturbed – and keep a close eye on it.
Not all perennials like to be moved and disturbing the roots can mean certain death. Some of the candidates for a very difficult relocation are Euphorbia polychroma (Cushion Spurge), Peonies, Bleeding Hearts, and Dictamnus (Gas Plant). This by no means is an exhaustive list; always do your research to double check that a perennial will tolerate being moved.
Remember, be gentle.