I've never planted the Dwarf Coreopsis (Nana) before, but I've read I should deadhead them to keep them blooming. My question is where? Do I just snip off the spent flower, partially down the stem, or at the base of the stem? It seemed odd to just pinch off the flower and leave the long stem, so I was leaning toward snipping at the base of the stem. I'm pretty new to becoming a better gardener, and I'd really like to get the most out of my plants. Thanks for any help!