The best mulch for flowers is organic hardwood bark mulch. Hardwood bark mulch is richer in nutrients than regular bark mulch, but it is more expensive. However, regular bark mulch is a good substitute.
Bark-based mulches are beneficial because they help suppress weeds and retain moisture, and they slowly break down over time, adding nutrients to the soil. Other organic mulches such as pine straw and hay do not provide the same nutrients as bark. Mulches are mostly prepared locally, so there is no single best nationwide brand. Check local nurseries and garden centers for options. Look for bark-based mulches with added organic material, such as compost. The added compost provides more nutrients that improve the soil for flowers to thrive.