Divide to Multiply
There are people who figure that perennials can be planted once and then forgotten. Unfortunately, it doesn’t work quite that way. As the plants grow and fill in you will need to dig and divide them. You can rework the soil and replant them right back into the same spots if they were successful there the first time, but you’ll end up with many extras which you’ll either need to give away, plant elsewhere or discard.
The frequency with which you’ll have to divide different perennials will vary. Shasta daises will probably need it every year, or every-other year at the longest. Species tulips and fall crocus (Sternbergia lutea) may never have to be dug unless you want to get a fresh start of them elsewhere. In general, however, you’re probably looking at redoing any given planting every 3 or 4 years.
Fall is the best time to get all of this done. Work when the soil is moist but not soggy. Use a sharpshooter or nursery spade to lift the clumps carefully. Lay them out on the driveway or in the wheelbarrow and break or cut them into smaller clumps. That might be into individual "fans" for daylilies and iris, or it could be into tennis-ball-sized clumps for smaller plants like oxalis, violets and ferns.
Have the new ground prepared ahead of time if you can, or rework existing soil immediately after you dig the plants. Replant as quickly as you can. If there is extensive green foliage as there will be with iris, daylilies, hardy amaryllis and ornamental grasses, it can be trimmed back by half to reduce the demands made of the root system. Water the new plantings right away.
By dividing and resetting your spring-flowering perennials now you’ll give them the best possible chance to get established for a good spring bloom starting next year.