You may prune your Dead Nettle plants whenever you see dead or dying limbs but do so carefully. It is important not to prune your plants during the winter because it could disrupt their next growing season if you cut the wrong part of the plant. During their growing season, you can prune your plants once their blossoms look like they are spent. Doing so will remove dying flowers and make space for new, fresh foliage to grow. You will remove old parts of the plant that your Lamium is focusing its energy on and providing new space for your plant to refocus its energy on instead.