Do your plants seem to have fewer flowers? Are they rootbound or outgrowing their pots? Do you just want more of them?
Use your hori hori to divide those plants! The Japanese gardening knife is an excellent choice to dig them up, pry or cut them apart, dig new holes and replant them.
Spring is the best time to divide plants that bloom in the summer and fall. For spring-blooming plants, it is better to wait to divide them until the fall or after they have bloomed.
In her article for "The World" Kym Pokorny at Oregon State University provides an excellent overview about dividing plants.