Dividing perennials is one of my least favorite chores in the garden. I think my favorite chores are raking the yard and pruning with my hand clippers. Anyhow, now is the time to divide perennials. There are two general reasons to divide perennials, one is to make more of the perennial and the other is to rejuvenate an overgrown perennial. Fall is the ideal time to divide because the plant is usually ready to go dormant, there is plentiful moisture, and the soil is still warm enough for good root growth. I think it is important to time the division so that the perennial can get reestablished before really cold weather sets in, but as long as there is moisture in the ground and the ground is not frozen, you can probably divide up to December, then begin again in February.
Some perennials which should be divided at some point are: Red hot Pokers, daylillies, shasta daisies, hostas, sedums, irises, coreopsis, yarrows, lambs ears, oreganos, cone flowers, brown eyed susans, dianthus, phlox, ornamental grasses, gladiolus, crocosmia, spireas, alliums, ferns, and peonies. This list is not all inclusive, just some that come to mind in my garden. Notably missing perennials include: Russian Sage, salvias, mums (although I have had success in dividing some mums), and gaura. I start these from cuttings because they do not divide well.
I have a very long and wide and perennial border on the north side of my property (pictured above). This border has been sparse for many years to say the least as it is so large and my budget does not allow for instant gratification. I have started shasta daisies from seed and planted them, divided daylillies and stuck them in here and many other plants but the border has not been full because I have had to spread out the plants. My plan was to repeat everything in a uniform manner. I made sure I planted one daylily every five feet and one shasta every five feet and so on. The problem is one of anything does not work in a large garden, even if it is repeated every five feet. My saving grace was the fact I knew all of the perennials I planted would eventually grow enough they could be divided. The time has come! Where I had just one shasta I now have five or six. They will still be thin for a year or two but they will fill in and make the impact in this border I am seeking. The cost in dollars to increase your plantings from division is ZERO-so what a bargain. The costs wind up being the amount of time of you are willing to wait before you can divide your one of everything.
in the garden....