Spend some time collecting your yard waste this fall in a pile / compost bin / compost barrel. This pile will start to decompose over the winter (if you can keep the pile for two years it will be very good compost). You can then use this material to mulch your flowers in the spring instead of purchasing expensive potting soils and fertilizers. Nature will do the work for you if you just let it.
For more tips on composting, check out my blog entry here.
For some more tips on saving money, check out my blog entry here.