Are these perennial flowers we’re talking about? Leave the stems attached until the birds in your area have eaten the seeds so they fare better over the winter. Seed heads will also catch snow and ice to create “winter interest” as it’s called in landscaping circles, giving your garden something pretty to look at even in the depths of winter. Those upright stems will also provide critical habitat for insects - they can provide that habitat if they’re cut and left whole on the ground but will become inaccessible if you get an early snow that lingers.