Spirea is easy. It actually sends out little sucker plants, so the first thing I'd suggest is to look around the base and see if any little ones (may be very small) are popping up. If so, just dig it out, pot it up, and voila!

If not, you can try rooting a stem that's still on the plant. Find a long flexible stem that will easily bend back to ground. Pin it mid-stem to the soil with something like an unbent paperclip. Pile a little moist soil on the spot, and wait 2-3 weeks to seee if roots develop. When they do, just cut it lose from the parent and dig it up.

You can also do cuttings. Object is to help cut piece develop roots BEFORE it either rots or dries out. Stick piece in half and half peat/perlite. Dipping end in rooting hormone helps. Keep top of cutting humidified by spraying. Put in bright light, but never direct sun. For spirea, I'd expect roots this time of year in about 2-3 weeks. It may well root in pot of moist garden soil without hormone and without spraying - optimizing these things just helps you get a larger proportion rooted. Not all will root in any case, so try several at a time.

This is an addiction, beware. We have been discussing on the Carolina Forum how we divide and take cuttings until original plants are dessimated. lol. There is no 12-step program for propagationism.